SEC Info℠  
    Home      Search      My Interests      Help      Sign In      Please Sign In

Summit Materials, Inc., et al. – ‘10-Q’ for 7/2/22 – ‘EX-101.DEF’

On:  Thursday, 8/4/22, at 11:37am ET   ·   For:  7/2/22   ·   Accession #:  1628280-22-20918   ·   File #s:  1-36873, 333-187556

Previous ‘10-Q’:  ‘10-Q’ on 5/5/22 for 4/2/22   ·   Next:  ‘10-Q’ on 11/3/22 for 10/1/22   ·   Latest:  ‘10-Q’ on 5/2/24 for 3/30/24   ·   4 References:   

Find Words in Filings emoji
 		  in    Show  and   ↓Hints

  As Of               Filer                 Filing    For·On·As Docs:Size             Issuer                      Filing Agent

 8/04/22  Summit Materials, Inc.            10-Q        7/02/22   89:19M                                    Workiva Inc Wde… FA01/FA
          Summit Materials, LLC

Quarterly Report   —   Form 10-Q

Filing Table of Contents

Document/Exhibit                   Description                      Pages   Size 

 1: 10-Q        Quarterly Report                                    HTML   2.40M 
10: EX-95.1     Mine-Safety Disclosure                              HTML   1.19M 
11: EX-99.1     Miscellaneous Exhibit                               HTML   1.86M 
 2: EX-31.1     Certification -- §302 - SOA'02                      HTML     29K 
 3: EX-31.2     Certification -- §302 - SOA'02                      HTML     28K 
 4: EX-31.3     Certification -- §302 - SOA'02                      HTML     28K 
 5: EX-31.4     Certification -- §302 - SOA'02                      HTML     28K 
 6: EX-32.1     Certification -- §906 - SOA'02                      HTML     26K 
 7: EX-32.2     Certification -- §906 - SOA'02                      HTML     26K 
 8: EX-32.3     Certification -- §906 - SOA'02                      HTML     26K 
 9: EX-32.4     Certification -- §906 - SOA'02                      HTML     26K 
17: R1          Cover                                               HTML     90K 
18: R2          Consolidated Balance Sheets                         HTML    174K 
19: R3          Consolidated Balance Sheets (Parenthetical)         HTML     46K 
20: R4          Unaudited Consolidated Statements of Operations     HTML    138K 
21: R5          Unaudited Consolidated Statements of Comprehensive  HTML     66K 
                Income                                                           
22: R6          Unaudited Consolidated Statements of Cash Flows     HTML    134K 
23: R7          Unaudited Consolidated Statements of Changes in     HTML    156K 
                Stockholders' Equity / Members' Interest                         
24: R8          Summary of Organization and Significant Accounting  HTML     54K 
                Policies                                                         
25: R9          Acquisitions, Dispostions, Goodwill and             HTML    152K 
                Intangibles                                                      
26: R10         Revenue Recognition                                 HTML     88K 
27: R11         Inventories                                         HTML     43K 
28: R12         Accrued Expenses                                    HTML     52K 
29: R13         Debt                                                HTML     97K 
30: R14         Income Taxes                                        HTML     38K 
31: R15         Earnings Per Share                                  HTML     68K 
32: R16         Stockholders' Equity/Members' Interest              HTML     95K 
33: R17         Supplemental Cash Flow Information                  HTML     53K 
34: R18         Leases                                              HTML    217K 
35: R19         Commitments and Contingencies                       HTML     39K 
36: R20         Fair Value                                          HTML     73K 
37: R21         Segment Information                                 HTML    200K 
38: R22         Guarantor and Non-Guarantor Financial Information   HTML    435K 
39: R23         Summary of Organization and Significant Accounting  HTML     70K 
                Policies - (Policies)                                            
40: R24         Acquisitions, Dispostions, Goodwill and             HTML    158K 
                Intangibles - (Tables)                                           
41: R25         Revenue Recognition - (Tables)                      HTML     88K 
42: R26         Inventories - (Tables)                              HTML     44K 
43: R27         Accrued Expenses - (Tables)                         HTML     51K 
44: R28         Debt - (Tables)                                     HTML     81K 
45: R29         Earnings Per Share - (Tables)                       HTML     69K 
46: R30         Stockholders' Equity/Members' Interest - (Tables)   HTML     89K 
47: R31         Supplemental Cash Flow Information - (Tables)       HTML     52K 
48: R32         Leases - (Tables)                                   HTML    398K 
49: R33         Fair Value - (Tables)                               HTML     68K 
50: R34         Segment Information - (Tables)                      HTML    192K 
51: R35         Guarantor and Non-Guarantor Financial Information   HTML    402K 
                - (Tables)                                                       
52: R36         SUMMARY OF ORGANIZATION AND SIGNIFICANT ACCOUNTING  HTML     37K 
                POLICIES - General Information (Details)                         
53: R37         SUMMARY OF ORGANIZATION AND SIGNIFICANT ACCOUNTING  HTML     29K 
                POLICIES - Business and Credit Concentration, Tax                
                Receivable Agreement (Details)                                   
54: R38         SUMMARY OF ORGANIZATION AND SIGNIFICANT ACCOUNTING  HTML     30K 
                POLICIES - Prior Period Reclassifications                        
                (Details)                                                        
55: R39         ACQUISITIONS, DISPOSTIONS, GOODWILL AND             HTML     33K 
                INTANGIBLES - Acquisitions by Region (Details)                   
56: R40         ACQUISITIONS, DISPOSTIONS, GOODWILL AND             HTML     68K 
                INTANGIBLES - Summary of Assets Acquired and                     
                Liabilities Assumed (Details)                                    
57: R41         ACQUISITIONS, DISPOSTIONS, GOODWILL AND             HTML     49K 
                INTANGIBLES - Summary of Goodwill by Reportable                  
                Segments (Details)                                               
58: R42         ACQUISITIONS, DISPOSTIONS, GOODWILL AND             HTML     57K 
                INTANGIBLES - Intangible Assets By Type (Details)                
59: R43         ACQUISITIONS, DISPOSTIONS, GOODWILL AND             HTML     56K 
                INTANGIBLES - Amortization Expense (Details)                     
60: R44         ACQUISITIONS, DISPOSTIONS, GOODWILL AND             HTML     38K 
                INTANGIBLES - Narrative (Details)                                
61: R45         REVENUE RECOGNITION - By Product (Details)          HTML     55K 
62: R46         REVENUE RECOGNITION - Summary of Accounts           HTML     51K 
                Receivable, Net (Details)                                        
63: R47         INVENTORIES - Components of Inventories (Details)   HTML     40K 
64: R48         ACCRUED EXPENSES - Components of Accrued Expenses   HTML     49K 
                (Details)                                                        
65: R49         DEBT - Schedule of Debt (Details)                   HTML     57K 
66: R50         DEBT - Schedule of Contractual Payments of          HTML     59K 
                Long-Term Debt (Details)                                         
67: R51         DEBT - Senior Notes (Details)                       HTML     50K 
68: R52         DEBT - Senior Secured Credit Facilities (Details)   HTML     67K 
69: R53         DEBT - Summary of Activity for Deferred Financing   HTML     34K 
                Fees (Details)                                                   
70: R54         DEBT - Other (Details)                              HTML     52K 
71: R55         INCOME TAXES - Narrative (Details)                  HTML     54K 
72: R56         EARNINGS PER SHARE - Schedule of Basic to Diluted   HTML     80K 
                Income Per Share (Details)                                       
73: R57         STOCKHOLDERS' EQUITY/MEMBERS' INTEREST - Narrative  HTML     40K 
                (Details)                                                        
74: R58         STOCKHOLDERS' EQUITY/MEMBERS' INTEREST - Equity     HTML     57K 
                Offerings (Details)                                              
75: R59         STOCKHOLDERS' EQUITY/MEMBERS' INTEREST -            HTML     54K 
                Accumulated Other Comprehensive Income (Loss)                    
                (Details)                                                        
76: R60         SUPPLEMENTAL CASH FLOW INFORMATION - Schedule of    HTML     51K 
                Supplemental Cash Flow Information (Details)                     
77: R61         LEASES - Operating and Finance Leases (Details)     HTML    154K 
78: R62         COMMITMENTS AND CONTINGENCIES - Narrative           HTML     43K 
                (Details)                                                        
79: R63         FAIR VALUE - Fair Value Measurements (Details)      HTML     43K 
80: R64         FAIR VALUE - Carrying Value and Fair Value of       HTML     51K 
                Financial Instruments (Details)                                  
81: R65         SEGMENT INFORMATION - Financial Data (Details)      HTML    122K 
82: R66         GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION   HTML    198K 
                - Schedule of Condensed Consolidating Balance                    
                Sheets (Details)                                                 
83: R67         GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION   HTML    102K 
                - Schedule of Condensed Consolidating Statements                 
                of Operations (Details)                                          
84: R68         GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION   HTML    115K 
                - Schedule of Condensed Consolidating Statements                 
                of Cash Flows (Details)                                          
87: XML         IDEA XML File -- Filing Summary                      XML    154K 
85: XML         XBRL Instance -- sum-20220702_htm                    XML   5.99M 
86: EXCEL       IDEA Workbook of Financial Reports                  XLSX    192K 
13: EX-101.CAL  XBRL Calculations -- sum-20220702_cal                XML    326K 
14: EX-101.DEF  XBRL Definitions -- sum-20220702_def                 XML   1.36M 
15: EX-101.LAB  XBRL Labels -- sum-20220702_lab                      XML   1.75M 
16: EX-101.PRE  XBRL Presentations -- sum-20220702_pre               XML   1.41M 
12: EX-101.SCH  XBRL Schema -- sum-20220702                          XSD    179K 
88: JSON        XBRL Instance as JSON Data -- MetaLinks              448±   709K 
89: ZIP         XBRL Zipped Folder -- 0001628280-22-020918-xbrl      Zip    900K

‘EX-101.DEF’   —   XBRL Definitions — sum-20220702_def

This Exhibit is an XBRL XML File.

                                                                                                                                                                                
<?xml version="1.0" encoding="windows-1252"?>
<!-- XBRL Document Created with Wdesk from Workiva -->
<!-- Copyright 2022 Workiva -->
<!-- r:f862892d-86d9-45b1-8a59-0358204f01fa,g:0fd08e0b-8e15-4464-b2ed-f7d1733b770c -->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
<link:roleRef roleURI="http://www.summitmaterials.com/role/Cover" xlink:type="simple" xlink:href="sum-20220702.xsd#Cover"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/Cover" xlink:type="extended" id="ic6516e616c4e4e75a206dc906655ed59_Cover">
<link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentInformationLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_ce4b3a8e-1750-4a8b-b321-5c371ec1d6b1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentType"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_DocumentType_ce4b3a8e-1750-4a8b-b321-5c371ec1d6b1" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_9074550c-958a-4131-8f44-a812d4c9f3c9" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentQuarterlyReport"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_DocumentQuarterlyReport_9074550c-958a-4131-8f44-a812d4c9f3c9" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_c69a91b0-892c-41de-a4d7-1b4b475c302a" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentPeriodEndDate"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_DocumentPeriodEndDate_c69a91b0-892c-41de-a4d7-1b4b475c302a" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_0ac88d7c-fed1-472b-a6df-a833cc56c9ad" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentTransitionReport"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_DocumentTransitionReport_0ac88d7c-fed1-472b-a6df-a833cc56c9ad" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_7caf1bc6-14fe-49f2-8cc4-87d7b57bb5d4" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityFileNumber"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityFileNumber_7caf1bc6-14fe-49f2-8cc4-87d7b57bb5d4" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_b79ec22f-fa89-4244-9799-eb79e133b9aa" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityRegistrantName"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityRegistrantName_b79ec22f-fa89-4244-9799-eb79e133b9aa" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_186d3eb9-950d-44fc-8d68-35ccca8863f3" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityIncorporationStateCountryCode"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityIncorporationStateCountryCode_186d3eb9-950d-44fc-8d68-35ccca8863f3" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_1e1e35d1-9ea2-4fef-96d6-46f559a07aaa" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityTaxIdentificationNumber"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityTaxIdentificationNumber_1e1e35d1-9ea2-4fef-96d6-46f559a07aaa" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_fddd55e5-e161-4647-8c87-9a40033fd634" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressAddressLine1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityAddressAddressLine1_fddd55e5-e161-4647-8c87-9a40033fd634" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_e735a6ca-0e67-47db-b97f-ea0fbb97e2da" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressAddressLine2"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityAddressAddressLine2_e735a6ca-0e67-47db-b97f-ea0fbb97e2da" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_312e2688-9cd1-4bd2-8cd9-36f5cc6ffbc1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressCityOrTown"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityAddressCityOrTown_312e2688-9cd1-4bd2-8cd9-36f5cc6ffbc1" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_9ee832d7-9c64-45c0-afa5-acd931c1d8f9" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressStateOrProvince"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityAddressStateOrProvince_9ee832d7-9c64-45c0-afa5-acd931c1d8f9" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_a7f9711c-be87-4829-ab41-9ed28ff617d3" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityAddressPostalZipCode"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityAddressPostalZipCode_a7f9711c-be87-4829-ab41-9ed28ff617d3" xlink:type="arc" order="12"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_fb72595c-bc23-4613-a298-fcb6b548397e" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_CityAreaCode"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_CityAreaCode_fb72595c-bc23-4613-a298-fcb6b548397e" xlink:type="arc" order="13"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_035b42bd-c63e-48f4-9eae-efed4cb7b22e" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LocalPhoneNumber"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_LocalPhoneNumber_035b42bd-c63e-48f4-9eae-efed4cb7b22e" xlink:type="arc" order="14"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_63e0185f-0a85-41a5-af72-96586d037f98" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_Security12bTitle"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_Security12bTitle_63e0185f-0a85-41a5-af72-96586d037f98" xlink:type="arc" order="15"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_dc9bb5ea-a19d-40da-bd05-d211fa71008d" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_TradingSymbol"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_TradingSymbol_dc9bb5ea-a19d-40da-bd05-d211fa71008d" xlink:type="arc" order="16"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_6fa40c73-5b02-4158-b428-af486c151ec6" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_SecurityExchangeName"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_SecurityExchangeName_6fa40c73-5b02-4158-b428-af486c151ec6" xlink:type="arc" order="17"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_e2901182-1e40-4703-b96a-285d19acc460" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityCurrentReportingStatus"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityCurrentReportingStatus_e2901182-1e40-4703-b96a-285d19acc460" xlink:type="arc" order="18"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_dc97b9ab-75fd-42a1-a400-b5bcde0c10f7" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityInteractiveDataCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityInteractiveDataCurrent_dc97b9ab-75fd-42a1-a400-b5bcde0c10f7" xlink:type="arc" order="19"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_0813e04f-82a6-44b0-a6bd-8a64c0e226ed" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityFilerCategory"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityFilerCategory_0813e04f-82a6-44b0-a6bd-8a64c0e226ed" xlink:type="arc" order="20"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_0ae3e4dc-19f9-46a0-9a16-9e155f216b44" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntitySmallBusiness"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntitySmallBusiness_0ae3e4dc-19f9-46a0-9a16-9e155f216b44" xlink:type="arc" order="21"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_4423b4e7-f309-476a-9c24-80637be24af0" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityEmergingGrowthCompany"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityEmergingGrowthCompany_4423b4e7-f309-476a-9c24-80637be24af0" xlink:type="arc" order="22"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_b7a656ca-fc2c-4850-acd6-987136e3ffcf" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityShellCompany"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityShellCompany_b7a656ca-fc2c-4850-acd6-987136e3ffcf" xlink:type="arc" order="23"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_c991bcbc-5a49-4b0f-aa63-285c7496ad29" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityCommonStockSharesOutstanding"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_c991bcbc-5a49-4b0f-aa63-285c7496ad29" xlink:type="arc" order="24"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_4ead83d0-3a59-4a0a-aece-dd36fa14949a" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityCentralIndexKey"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_EntityCentralIndexKey_4ead83d0-3a59-4a0a-aece-dd36fa14949a" xlink:type="arc" order="25"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_cbe96f03-3a5d-4673-8247-43c0c51e95dc" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_AmendmentFlag"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_AmendmentFlag_cbe96f03-3a5d-4673-8247-43c0c51e95dc" xlink:type="arc" order="26"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_ac5b6626-a360-4cf3-8302-4ba2e4ad078b" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_CurrentFiscalYearEndDate"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_CurrentFiscalYearEndDate_ac5b6626-a360-4cf3-8302-4ba2e4ad078b" xlink:type="arc" order="27"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_29c31720-13fb-44a5-948d-54ec0871fb25" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentFiscalYearFocus"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_DocumentFiscalYearFocus_29c31720-13fb-44a5-948d-54ec0871fb25" xlink:type="arc" order="28"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_e2e5556b-39cf-4903-9f99-6c2f9b5f7cd8" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentFiscalPeriodFocus"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_DocumentFiscalPeriodFocus_e2e5556b-39cf-4903-9f99-6c2f9b5f7cd8" xlink:type="arc" order="29"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_49aa5967-c1e4-409d-8809-dfb34d711577" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_DocumentInformationTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_aee9e813-b955-495f-8099-772b1b10da12" xlink:to="loc_dei_DocumentInformationTable_49aa5967-c1e4-409d-8809-dfb34d711577" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a60a85de-5157-46d8-8c29-9ff19c710fe2" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_49aa5967-c1e4-409d-8809-dfb34d711577" xlink:to="loc_dei_LegalEntityAxis_a60a85de-5157-46d8-8c29-9ff19c710fe2" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a60a85de-5157-46d8-8c29-9ff19c710fe2_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a60a85de-5157-46d8-8c29-9ff19c710fe2" xlink:to="loc_dei_EntityDomain_a60a85de-5157-46d8-8c29-9ff19c710fe2_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_c212246a-6286-4c94-af5a-e45e442a82ec" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a60a85de-5157-46d8-8c29-9ff19c710fe2" xlink:to="loc_dei_EntityDomain_c212246a-6286-4c94-af5a-e45e442a82ec" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_b693a4f8-8b0e-46b2-a844-84524074243b" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_c212246a-6286-4c94-af5a-e45e442a82ec" xlink:to="loc_sum_SummitMaterialsLlcMember_b693a4f8-8b0e-46b2-a844-84524074243b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_e99779e4-553e-4c56-8f43-e500988e5644" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_49aa5967-c1e4-409d-8809-dfb34d711577" xlink:to="loc_us-gaap_StatementClassOfStockAxis_e99779e4-553e-4c56-8f43-e500988e5644" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_e99779e4-553e-4c56-8f43-e500988e5644_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e99779e4-553e-4c56-8f43-e500988e5644" xlink:to="loc_us-gaap_ClassOfStockDomain_e99779e4-553e-4c56-8f43-e500988e5644_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_ced44b56-8b1b-43a6-85b3-76851f894edc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e99779e4-553e-4c56-8f43-e500988e5644" xlink:to="loc_us-gaap_ClassOfStockDomain_ced44b56-8b1b-43a6-85b3-76851f894edc" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_3d1544d8-7169-4928-9d09-d1e1ebbbecda" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_ced44b56-8b1b-43a6-85b3-76851f894edc" xlink:to="loc_us-gaap_CommonClassAMember_3d1544d8-7169-4928-9d09-d1e1ebbbecda" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_9c5295b9-43c0-4792-9645-6b495025a3ff" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassBMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_ced44b56-8b1b-43a6-85b3-76851f894edc" xlink:to="loc_us-gaap_CommonClassBMember_9c5295b9-43c0-4792-9645-6b495025a3ff" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ConsolidatedBalanceSheets" xlink:type="simple" xlink:href="sum-20220702.xsd#ConsolidatedBalanceSheets"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ConsolidatedBalanceSheets" xlink:type="extended" id="ib3fa9184a6f145d78fd51d14b9671b94_ConsolidatedBalanceSheets">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_169c5a18-7d1f-48ad-b504-7b5be017d4cc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_76355074-8831-44d7-8003-c23c4826925c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_169c5a18-7d1f-48ad-b504-7b5be017d4cc" xlink:to="loc_us-gaap_AssetsAbstract_76355074-8831-44d7-8003-c23c4826925c" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_855dab91-6654-4404-942c-584a9fc94dce" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrentAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_76355074-8831-44d7-8003-c23c4826925c" xlink:to="loc_us-gaap_AssetsCurrentAbstract_855dab91-6654-4404-942c-584a9fc94dce" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_12261e63-a6ea-452a-a67a-dc3f73d42544" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_855dab91-6654-4404-942c-584a9fc94dce" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_12261e63-a6ea-452a-a67a-dc3f73d42544" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_f0a13d23-c010-416d-96e1-fce285335670" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableNetCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_855dab91-6654-4404-942c-584a9fc94dce" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_f0a13d23-c010-416d-96e1-fce285335670" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_62798c8c-f758-432f-928d-54c9161506b9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_855dab91-6654-4404-942c-584a9fc94dce" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_62798c8c-f758-432f-928d-54c9161506b9" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_81b5594f-61fd-4623-aab1-5e638525ffd7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_855dab91-6654-4404-942c-584a9fc94dce" xlink:to="loc_us-gaap_InventoryNet_81b5594f-61fd-4623-aab1-5e638525ffd7" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_b22d3d19-847f-494a-9f6f-0217e4978d3b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAssetsCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_855dab91-6654-4404-942c-584a9fc94dce" xlink:to="loc_us-gaap_OtherAssetsCurrent_b22d3d19-847f-494a-9f6f-0217e4978d3b" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationCurrent_564938da-ee05-45ab-9493-ba66a3425d68" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_855dab91-6654-4404-942c-584a9fc94dce" xlink:to="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationCurrent_564938da-ee05-45ab-9493-ba66a3425d68" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_4458e4b8-d3c6-4fc6-8c17-904037ead72a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_855dab91-6654-4404-942c-584a9fc94dce" xlink:to="loc_us-gaap_AssetsCurrent_4458e4b8-d3c6-4fc6-8c17-904037ead72a" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_1edd72b2-1b5e-4dfb-aafa-75e72386edd8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_76355074-8831-44d7-8003-c23c4826925c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_1edd72b2-1b5e-4dfb-aafa-75e72386edd8" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_05ed3d29-ffd1-47e4-927c-1c016ccc14ea" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_76355074-8831-44d7-8003-c23c4826925c" xlink:to="loc_us-gaap_Goodwill_05ed3d29-ffd1-47e4-927c-1c016ccc14ea" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_d1091889-02b9-43ac-a642-f936358519e9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_76355074-8831-44d7-8003-c23c4826925c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_d1091889-02b9-43ac-a642-f936358519e9" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxAssetsNet_20b9dc63-d076-4d6a-b185-c4b9f767903e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredIncomeTaxAssetsNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_76355074-8831-44d7-8003-c23c4826925c" xlink:to="loc_us-gaap_DeferredIncomeTaxAssetsNet_20b9dc63-d076-4d6a-b185-c4b9f767903e" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_b43ecbc8-10a2-4e59-8ab5-1fab171ce073" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_76355074-8831-44d7-8003-c23c4826925c" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_b43ecbc8-10a2-4e59-8ab5-1fab171ce073" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_77065e2f-9441-4ec5-b5ec-2eeac8099716" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAssetsNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_76355074-8831-44d7-8003-c23c4826925c" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_77065e2f-9441-4ec5-b5ec-2eeac8099716" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_0aaf7d1b-2b6a-47e6-8bdd-26be30fb91d3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_76355074-8831-44d7-8003-c23c4826925c" xlink:to="loc_us-gaap_Assets_0aaf7d1b-2b6a-47e6-8bdd-26be30fb91d3" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_169c5a18-7d1f-48ad-b504-7b5be017d4cc" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_d35e86ae-574d-48a2-8a2a-a63fbd25bb38" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_d35e86ae-574d-48a2-8a2a-a63fbd25bb38" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_300eaf79-7eac-4e4d-8433-d35ce29ebc07" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d35e86ae-574d-48a2-8a2a-a63fbd25bb38" xlink:to="loc_us-gaap_LongTermDebtCurrent_300eaf79-7eac-4e4d-8433-d35ce29ebc07" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AcquisitionRelatedLiabilitiesCurrent_7964442f-5889-4699-b2f3-e6ab4343ea5c" xlink:href="sum-20220702.xsd#sum_AcquisitionRelatedLiabilitiesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d35e86ae-574d-48a2-8a2a-a63fbd25bb38" xlink:to="loc_sum_AcquisitionRelatedLiabilitiesCurrent_7964442f-5889-4699-b2f3-e6ab4343ea5c" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_e5ed8f9b-dffa-41c5-9ce1-f0d95b11b219" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsPayableCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d35e86ae-574d-48a2-8a2a-a63fbd25bb38" xlink:to="loc_us-gaap_AccountsPayableCurrent_e5ed8f9b-dffa-41c5-9ce1-f0d95b11b219" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_e180ddc8-4c18-4005-a525-ff1976db996b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d35e86ae-574d-48a2-8a2a-a63fbd25bb38" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_e180ddc8-4c18-4005-a525-ff1976db996b" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_f378573d-06ae-45aa-adeb-afcbdf3260ba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d35e86ae-574d-48a2-8a2a-a63fbd25bb38" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_f378573d-06ae-45aa-adeb-afcbdf3260ba" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_db1a5e28-4b1d-4a30-8c8e-86d5496e6f98" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d35e86ae-574d-48a2-8a2a-a63fbd25bb38" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_db1a5e28-4b1d-4a30-8c8e-86d5496e6f98" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_9857377d-eb9d-4f51-8eea-30e506dbf3c5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d35e86ae-574d-48a2-8a2a-a63fbd25bb38" xlink:to="loc_us-gaap_LiabilitiesCurrent_9857377d-eb9d-4f51-8eea-30e506dbf3c5" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_LongTermDebtNoncurrentNet_4054112e-c538-4d56-a205-e4cf7c051e47" xlink:href="sum-20220702.xsd#sum_LongTermDebtNoncurrentNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:to="loc_sum_LongTermDebtNoncurrentNet_4054112e-c538-4d56-a205-e4cf7c051e47" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AcquisitionRelatedLiabilitiesNonCurrent_0df26608-56a5-4ee2-9524-06c14f9231ad" xlink:href="sum-20220702.xsd#sum_AcquisitionRelatedLiabilitiesNonCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:to="loc_sum_AcquisitionRelatedLiabilitiesNonCurrent_0df26608-56a5-4ee2-9524-06c14f9231ad" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_TaxReceivableAgreementLiability_8a714218-da42-4eaf-bce1-8dac88cd6756" xlink:href="sum-20220702.xsd#sum_TaxReceivableAgreementLiability"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:to="loc_sum_TaxReceivableAgreementLiability_8a714218-da42-4eaf-bce1-8dac88cd6756" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_ed3d2a3f-a4ef-4259-9ca9-2a436a74fbef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_ed3d2a3f-a4ef-4259-9ca9-2a436a74fbef" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_d70005e5-e07d-4e36-bdbe-090fcc72828b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_d70005e5-e07d-4e36-bdbe-090fcc72828b" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_937d6983-8361-460a-9fd2-fa412cda27cc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Liabilities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:to="loc_us-gaap_Liabilities_937d6983-8361-460a-9fd2-fa412cda27cc" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_003d6548-4859-4e9a-9315-4f49cca81f1c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommitmentsAndContingencies"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:to="loc_us-gaap_CommitmentsAndContingencies_003d6548-4859-4e9a-9315-4f49cca81f1c" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:to="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_b7eb2f96-ef02-442c-8e75-1449369c0877" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:to="loc_us-gaap_CommonStockValue_b7eb2f96-ef02-442c-8e75-1449369c0877" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersCapital_c09a9511-067a-4fc7-98b1-bcc3b15525b2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MembersCapital"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:to="loc_us-gaap_MembersCapital_c09a9511-067a-4fc7-98b1-bcc3b15525b2" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_86345dd0-9e74-437a-b2bd-45a0bda47429" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_86345dd0-9e74-437a-b2bd-45a0bda47429" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_4dd9d1bb-56be-4237-b886-955ae6f87fff" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_4dd9d1bb-56be-4237-b886-955ae6f87fff" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_2402ed7a-88f5-43a3-92a0-306e54d8374e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_2402ed7a-88f5-43a3-92a0-306e54d8374e" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_50fd6b7f-9d58-4036-bff1-21753fb0cedf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:to="loc_us-gaap_StockholdersEquity_50fd6b7f-9d58-4036-bff1-21753fb0cedf" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_StockholdersEquityAttributableToNoncontrollingInterestExcludingPortionAttributableToNoncontrollingInterestOfWhollyOwnedIndirectSubsidiaryOfRegistrant_c8023c63-1c74-42d1-9035-2e7ad12daf18" xlink:href="sum-20220702.xsd#sum_StockholdersEquityAttributableToNoncontrollingInterestExcludingPortionAttributableToNoncontrollingInterestOfWhollyOwnedIndirectSubsidiaryOfRegistrant"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:to="loc_sum_StockholdersEquityAttributableToNoncontrollingInterestExcludingPortionAttributableToNoncontrollingInterestOfWhollyOwnedIndirectSubsidiaryOfRegistrant_c8023c63-1c74-42d1-9035-2e7ad12daf18" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_7f5bad49-3a29-4f37-9716-57ff1a9f42e5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_7f5bad49-3a29-4f37-9716-57ff1a9f42e5" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_d5a59ec8-f3c9-4e68-a754-85031e49da74" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_825e2d23-acef-4f31-9be4-ad166b3a64c3" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_d5a59ec8-f3c9-4e68-a754-85031e49da74" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_851f469a-4188-482d-ac19-0b842f03ac84" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_42540a6d-46d4-43b9-b214-ef30135d1233" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_851f469a-4188-482d-ac19-0b842f03ac84" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_033fb83e-b776-4f4b-81a5-697ccfa58694" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_169c5a18-7d1f-48ad-b504-7b5be017d4cc" xlink:to="loc_us-gaap_StatementTable_033fb83e-b776-4f4b-81a5-697ccfa58694" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_0044136c-675a-4bc4-b32d-fa9dae187dbd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_033fb83e-b776-4f4b-81a5-697ccfa58694" xlink:to="loc_us-gaap_StatementClassOfStockAxis_0044136c-675a-4bc4-b32d-fa9dae187dbd" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0044136c-675a-4bc4-b32d-fa9dae187dbd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_0044136c-675a-4bc4-b32d-fa9dae187dbd" xlink:to="loc_us-gaap_ClassOfStockDomain_0044136c-675a-4bc4-b32d-fa9dae187dbd_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9a237d4d-38f7-4700-a075-8cb92d924025" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_0044136c-675a-4bc4-b32d-fa9dae187dbd" xlink:to="loc_us-gaap_ClassOfStockDomain_9a237d4d-38f7-4700-a075-8cb92d924025" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_df202447-133f-4a0a-96c1-111fd82770eb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9a237d4d-38f7-4700-a075-8cb92d924025" xlink:to="loc_us-gaap_CommonClassAMember_df202447-133f-4a0a-96c1-111fd82770eb" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_d8ae32c6-ac98-4a97-b6df-1d34a189ee2f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassBMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9a237d4d-38f7-4700-a075-8cb92d924025" xlink:to="loc_us-gaap_CommonClassBMember_d8ae32c6-ac98-4a97-b6df-1d34a189ee2f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_58a7d1fa-dc29-43f0-bf89-b4922c468348" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_033fb83e-b776-4f4b-81a5-697ccfa58694" xlink:to="loc_dei_LegalEntityAxis_58a7d1fa-dc29-43f0-bf89-b4922c468348" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_58a7d1fa-dc29-43f0-bf89-b4922c468348_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_58a7d1fa-dc29-43f0-bf89-b4922c468348" xlink:to="loc_dei_EntityDomain_58a7d1fa-dc29-43f0-bf89-b4922c468348_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e2f31535-cbc4-4c7e-84cf-0e7e97a478f3" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_58a7d1fa-dc29-43f0-bf89-b4922c468348" xlink:to="loc_dei_EntityDomain_e2f31535-cbc4-4c7e-84cf-0e7e97a478f3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_f40469c9-3859-4dbd-9a79-e67572972d7c" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_e2f31535-cbc4-4c7e-84cf-0e7e97a478f3" xlink:to="loc_sum_SummitMaterialsLlcMember_f40469c9-3859-4dbd-9a79-e67572972d7c" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="sum-20220702.xsd#ConsolidatedBalanceSheetsParenthetical"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended" id="i70d456d2d8134506a26a302a263e5f25_ConsolidatedBalanceSheetsParenthetical">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_3e13cf5a-9b37-4957-865d-ea784ab96895" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_ede47505-3044-45a8-b1cf-1bd27a37e325" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e13cf5a-9b37-4957-865d-ea784ab96895" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_ede47505-3044-45a8-b1cf-1bd27a37e325" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_3454e1c9-be62-4a20-9862-ef101b876869" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e13cf5a-9b37-4957-865d-ea784ab96895" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_3454e1c9-be62-4a20-9862-ef101b876869" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowance_476d29a1-0d9e-48da-a73e-e77e4f099947" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsValuationAllowance"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e13cf5a-9b37-4957-865d-ea784ab96895" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowance_476d29a1-0d9e-48da-a73e-e77e4f099947" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_fe2d338c-1169-4b9c-88ac-0a9ad36daf72" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e13cf5a-9b37-4957-865d-ea784ab96895" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_fe2d338c-1169-4b9c-88ac-0a9ad36daf72" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_8e39176c-2b4c-479c-a7a8-3923e4c77c48" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesAuthorized"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e13cf5a-9b37-4957-865d-ea784ab96895" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_8e39176c-2b4c-479c-a7a8-3923e4c77c48" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_0c77a7c4-7a45-4935-ba5b-dae8875f32c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e13cf5a-9b37-4957-865d-ea784ab96895" xlink:to="loc_us-gaap_CommonStockSharesIssued_0c77a7c4-7a45-4935-ba5b-dae8875f32c3" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_a6a70994-930a-4b41-b976-404229d39efb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesOutstanding"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e13cf5a-9b37-4957-865d-ea784ab96895" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_a6a70994-930a-4b41-b976-404229d39efb" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_a872ea69-81e2-4bac-9001-a5dc784c379f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_3e13cf5a-9b37-4957-865d-ea784ab96895" xlink:to="loc_us-gaap_StatementTable_a872ea69-81e2-4bac-9001-a5dc784c379f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_fa54f22a-875c-44a3-80d8-5b7d98dbfb56" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_a872ea69-81e2-4bac-9001-a5dc784c379f" xlink:to="loc_us-gaap_StatementClassOfStockAxis_fa54f22a-875c-44a3-80d8-5b7d98dbfb56" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_fa54f22a-875c-44a3-80d8-5b7d98dbfb56_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_fa54f22a-875c-44a3-80d8-5b7d98dbfb56" xlink:to="loc_us-gaap_ClassOfStockDomain_fa54f22a-875c-44a3-80d8-5b7d98dbfb56_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_62691ed7-0c25-4fc9-80a8-2a1144d5d57d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_fa54f22a-875c-44a3-80d8-5b7d98dbfb56" xlink:to="loc_us-gaap_ClassOfStockDomain_62691ed7-0c25-4fc9-80a8-2a1144d5d57d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_e368c125-8172-46f6-823d-e00ab8912c3b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_62691ed7-0c25-4fc9-80a8-2a1144d5d57d" xlink:to="loc_us-gaap_CommonClassAMember_e368c125-8172-46f6-823d-e00ab8912c3b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_ae699797-cad8-479f-a925-4de92f1cb5c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassBMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_62691ed7-0c25-4fc9-80a8-2a1144d5d57d" xlink:to="loc_us-gaap_CommonClassBMember_ae699797-cad8-479f-a925-4de92f1cb5c6" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_4a401425-c866-4542-b446-2c0a089afaef" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_a872ea69-81e2-4bac-9001-a5dc784c379f" xlink:to="loc_dei_LegalEntityAxis_4a401425-c866-4542-b446-2c0a089afaef" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_4a401425-c866-4542-b446-2c0a089afaef_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_4a401425-c866-4542-b446-2c0a089afaef" xlink:to="loc_dei_EntityDomain_4a401425-c866-4542-b446-2c0a089afaef_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_63bce678-f0bc-4bd7-a69f-cf7e3278bdbe" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_4a401425-c866-4542-b446-2c0a089afaef" xlink:to="loc_dei_EntityDomain_63bce678-f0bc-4bd7-a69f-cf7e3278bdbe" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_8162be0b-ea27-42f0-855b-b50eb0ed11da" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_63bce678-f0bc-4bd7-a69f-cf7e3278bdbe" xlink:to="loc_sum_SummitMaterialsLlcMember_8162be0b-ea27-42f0-855b-b50eb0ed11da" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/UnauditedConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="sum-20220702.xsd#UnauditedConsolidatedStatementsofOperations"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/UnauditedConsolidatedStatementsofOperations" xlink:type="extended" id="i9b51efdc773a432bbc595795482343fe_UnauditedConsolidatedStatementsofOperations">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerAbstract_9883102f-254a-4088-9b45-d0cb11b871f6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerAbstract_9883102f-254a-4088-9b45-d0cb11b871f6" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_3faa708c-4f3c-4e50-96f8-d5482cf7ca57" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueFromContractWithCustomerAbstract_9883102f-254a-4088-9b45-d0cb11b871f6" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_3faa708c-4f3c-4e50-96f8-d5482cf7ca57" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_a74f65be-6836-4672-9e8c-8a36fcd06e7f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfGoodsAndServicesSoldAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_a74f65be-6836-4672-9e8c-8a36fcd06e7f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_6d5c9918-d77c-4932-9fbe-75a56feb971e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfGoodsAndServicesSoldAbstract_a74f65be-6836-4672-9e8c-8a36fcd06e7f" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_6d5c9918-d77c-4932-9fbe-75a56feb971e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_8d1b2f84-36e9-4226-b1dd-fceffd75626d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_8d1b2f84-36e9-4226-b1dd-fceffd75626d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_DepreciationDepletionAmortizationAndAccretion_766342e3-fa78-4468-acb9-aedc8fb63230" xlink:href="sum-20220702.xsd#sum_DepreciationDepletionAmortizationAndAccretion"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_sum_DepreciationDepletionAmortizationAndAccretion_766342e3-fa78-4468-acb9-aedc8fb63230" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_ddc5c11c-cee2-4966-b1dc-f835b6f3b2de" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_ddc5c11c-cee2-4966-b1dc-f835b6f3b2de" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_3e9fa1e3-7e23-41e8-8d52-f8e7e0904d91" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingIncomeLoss"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_OperatingIncomeLoss_3e9fa1e3-7e23-41e8-8d52-f8e7e0904d91" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_11877478-21ab-4773-ab51-23b0a19f2c5a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_InterestExpense_11877478-21ab-4773-ab51-23b0a19f2c5a" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_TaxReceivableAgreementExpense_c514bde8-412f-47d1-b471-9062986f6a23" xlink:href="sum-20220702.xsd#sum_TaxReceivableAgreementExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_sum_TaxReceivableAgreementExpense_c514bde8-412f-47d1-b471-9062986f6a23" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_e3c90481-6d9c-4baa-8537-68cc59deab74" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_e3c90481-6d9c-4baa-8537-68cc59deab74" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_30b2783b-19bb-48d4-83d3-828b3d34ef90" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_30b2783b-19bb-48d4-83d3-828b3d34ef90" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_babe6cab-ad27-4f97-a167-29f1ccbfb444" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_babe6cab-ad27-4f97-a167-29f1ccbfb444" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_f52aee4b-6481-42d7-9577-d56a9f003f96" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_f52aee4b-6481-42d7-9577-d56a9f003f96" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_76055a77-209b-429d-819b-c204df2e569d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProfitLoss"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_ProfitLoss_76055a77-209b-429d-819b-c204df2e569d" xlink:type="arc" order="12"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_NetIncomeLossAttributableToNoncontrollingInterestExcludingPortionAttributableToNoncontrollingInterestOfWhollyOwnedIndirectSubsidiaryOfRegistrant_da2fd241-a57e-4372-9916-326bae9f9306" xlink:href="sum-20220702.xsd#sum_NetIncomeLossAttributableToNoncontrollingInterestExcludingPortionAttributableToNoncontrollingInterestOfWhollyOwnedIndirectSubsidiaryOfRegistrant"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_sum_NetIncomeLossAttributableToNoncontrollingInterestExcludingPortionAttributableToNoncontrollingInterestOfWhollyOwnedIndirectSubsidiaryOfRegistrant_da2fd241-a57e-4372-9916-326bae9f9306" xlink:type="arc" order="13"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_420c4475-d3f1-4419-85bd-50a913666fff" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_420c4475-d3f1-4419-85bd-50a913666fff" xlink:type="arc" order="14"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_9c0ae857-4889-4782-a1e4-33c1e2a31639" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_EarningsPerShareAbstract_9c0ae857-4889-4782-a1e4-33c1e2a31639" xlink:type="arc" order="15"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_65f9a8fb-d2ce-4e58-9eba-da93339f3e48" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareBasic"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_9c0ae857-4889-4782-a1e4-33c1e2a31639" xlink:to="loc_us-gaap_EarningsPerShareBasic_65f9a8fb-d2ce-4e58-9eba-da93339f3e48" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_fef0cc23-bc1f-486e-b6dd-a9946bd1e95f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareDiluted"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_9c0ae857-4889-4782-a1e4-33c1e2a31639" xlink:to="loc_us-gaap_EarningsPerShareDiluted_fef0cc23-bc1f-486e-b6dd-a9946bd1e95f" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_30dfd144-a476-4245-b699-51eff6e9b516" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_30dfd144-a476-4245-b699-51eff6e9b516" xlink:type="arc" order="16"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_b7f27265-bdf3-4108-87f3-bd2d8bb0bb47" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_30dfd144-a476-4245-b699-51eff6e9b516" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_b7f27265-bdf3-4108-87f3-bd2d8bb0bb47" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_7f223dc5-3015-45be-bd9d-fdfbb474e2d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_30dfd144-a476-4245-b699-51eff6e9b516" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_7f223dc5-3015-45be-bd9d-fdfbb474e2d1" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_d11ddf09-f891-4290-a4e0-f258775fcd80" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_a630609c-5462-4d82-91ac-08458daebcad" xlink:to="loc_us-gaap_StatementTable_d11ddf09-f891-4290-a4e0-f258775fcd80" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_39300361-0e79-45c3-bfee-d54bb0674fb4" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_d11ddf09-f891-4290-a4e0-f258775fcd80" xlink:to="loc_srt_ProductOrServiceAxis_39300361-0e79-45c3-bfee-d54bb0674fb4" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_39300361-0e79-45c3-bfee-d54bb0674fb4_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_39300361-0e79-45c3-bfee-d54bb0674fb4" xlink:to="loc_srt_ProductsAndServicesDomain_39300361-0e79-45c3-bfee-d54bb0674fb4_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_75628297-ea29-4926-a5ec-cad424ab4404" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_39300361-0e79-45c3-bfee-d54bb0674fb4" xlink:to="loc_srt_ProductsAndServicesDomain_75628297-ea29-4926-a5ec-cad424ab4404" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ExcludingShippingAndHandlingMember_962b3718-3d17-48ba-a553-490ddb73c0c8" xlink:href="sum-20220702.xsd#sum_ExcludingShippingAndHandlingMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_75628297-ea29-4926-a5ec-cad424ab4404" xlink:to="loc_sum_ExcludingShippingAndHandlingMember_962b3718-3d17-48ba-a553-490ddb73c0c8" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_f238652e-2c88-4e39-83c9-2a4083d9b8fb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProductMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ExcludingShippingAndHandlingMember_962b3718-3d17-48ba-a553-490ddb73c0c8" xlink:to="loc_us-gaap_ProductMember_f238652e-2c88-4e39-83c9-2a4083d9b8fb" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_0fcaae98-0ba9-46c9-a3ce-c985ada3892a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ServiceMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ExcludingShippingAndHandlingMember_962b3718-3d17-48ba-a553-490ddb73c0c8" xlink:to="loc_us-gaap_ServiceMember_0fcaae98-0ba9-46c9-a3ce-c985ada3892a" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShippingAndHandlingMember_06ac117d-6720-458e-a1bf-ec1cf7bf7101" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShippingAndHandlingMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_75628297-ea29-4926-a5ec-cad424ab4404" xlink:to="loc_us-gaap_ShippingAndHandlingMember_06ac117d-6720-458e-a1bf-ec1cf7bf7101" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_b189f63d-8108-4fc6-8fa6-d6c00f6fb9c5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_d11ddf09-f891-4290-a4e0-f258775fcd80" xlink:to="loc_us-gaap_StatementClassOfStockAxis_b189f63d-8108-4fc6-8fa6-d6c00f6fb9c5" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_b189f63d-8108-4fc6-8fa6-d6c00f6fb9c5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_b189f63d-8108-4fc6-8fa6-d6c00f6fb9c5" xlink:to="loc_us-gaap_ClassOfStockDomain_b189f63d-8108-4fc6-8fa6-d6c00f6fb9c5_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_626d9a25-cfac-4eae-b90d-3d8a34da5b02" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_b189f63d-8108-4fc6-8fa6-d6c00f6fb9c5" xlink:to="loc_us-gaap_ClassOfStockDomain_626d9a25-cfac-4eae-b90d-3d8a34da5b02" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_d7432b0f-fa32-419b-848c-597cd208d240" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_626d9a25-cfac-4eae-b90d-3d8a34da5b02" xlink:to="loc_us-gaap_CommonClassAMember_d7432b0f-fa32-419b-848c-597cd208d240" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CommonClassAAndRestrictedStockMember_87f80d95-06e6-430f-a88d-9ee833de43d9" xlink:href="sum-20220702.xsd#sum_CommonClassAAndRestrictedStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_626d9a25-cfac-4eae-b90d-3d8a34da5b02" xlink:to="loc_sum_CommonClassAAndRestrictedStockMember_87f80d95-06e6-430f-a88d-9ee833de43d9" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_e97c39ce-21c5-4d78-afe0-72a6320cb427" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_d11ddf09-f891-4290-a4e0-f258775fcd80" xlink:to="loc_dei_LegalEntityAxis_e97c39ce-21c5-4d78-afe0-72a6320cb427" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e97c39ce-21c5-4d78-afe0-72a6320cb427_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_e97c39ce-21c5-4d78-afe0-72a6320cb427" xlink:to="loc_dei_EntityDomain_e97c39ce-21c5-4d78-afe0-72a6320cb427_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_54c3cb9a-637e-468d-9a61-2cf52be6fa85" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_e97c39ce-21c5-4d78-afe0-72a6320cb427" xlink:to="loc_dei_EntityDomain_54c3cb9a-637e-468d-9a61-2cf52be6fa85" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_9f1f7456-87c9-4743-9616-71ebe60db2f3" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_54c3cb9a-637e-468d-9a61-2cf52be6fa85" xlink:to="loc_sum_SummitMaterialsLlcMember_9f1f7456-87c9-4743-9616-71ebe60db2f3" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/UnauditedConsolidatedStatementsofComprehensiveIncome" xlink:type="simple" xlink:href="sum-20220702.xsd#UnauditedConsolidatedStatementsofComprehensiveIncome"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/UnauditedConsolidatedStatementsofComprehensiveIncome" xlink:type="extended" id="ied39c171b31947878c7be755ff40b6bd_UnauditedConsolidatedStatementsofComprehensiveIncome">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_713bf7f7-7569-40a5-b27f-fe9fc7799b3f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_786cc78a-5382-4905-bf3c-eecb55f753be" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTaxAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_713bf7f7-7569-40a5-b27f-fe9fc7799b3f" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_786cc78a-5382-4905-bf3c-eecb55f753be" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_fa5333bb-250f-4fa2-867f-058f3f70a76b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProfitLoss"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_786cc78a-5382-4905-bf3c-eecb55f753be" xlink:to="loc_us-gaap_ProfitLoss_fa5333bb-250f-4fa2-867f-058f3f70a76b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_f39ea4df-92bb-4377-86d4-229e0535d6f8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_786cc78a-5382-4905-bf3c-eecb55f753be" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_f39ea4df-92bb-4377-86d4-229e0535d6f8" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax_4125eac1-ac07-4948-8581-4e18b355afc1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_f39ea4df-92bb-4377-86d4-229e0535d6f8" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax_4125eac1-ac07-4948-8581-4e18b355afc1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTax_df789082-05ec-43fa-835b-23e3e9b7cdd2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_f39ea4df-92bb-4377-86d4-229e0535d6f8" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTax_df789082-05ec-43fa-835b-23e3e9b7cdd2" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_487e4d41-d01c-46be-9b8a-d68a894cd34d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_f39ea4df-92bb-4377-86d4-229e0535d6f8" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_487e4d41-d01c-46be-9b8a-d68a894cd34d" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_cd993044-3601-4655-a5d7-18e32ca33c61" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_786cc78a-5382-4905-bf3c-eecb55f753be" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_cd993044-3601-4655-a5d7-18e32ca33c61" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ComprehensiveIncomeLossNetOfTaxAttributableToNoncontrollingInterestExcludingPortionAttributableToNoncontrollingInterestOfWhollyOwnedIndirectSubsidiaryOfRegistrant_b5bb5ee4-476c-44fb-827a-dd1d35983778" xlink:href="sum-20220702.xsd#sum_ComprehensiveIncomeLossNetOfTaxAttributableToNoncontrollingInterestExcludingPortionAttributableToNoncontrollingInterestOfWhollyOwnedIndirectSubsidiaryOfRegistrant"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_786cc78a-5382-4905-bf3c-eecb55f753be" xlink:to="loc_sum_ComprehensiveIncomeLossNetOfTaxAttributableToNoncontrollingInterestExcludingPortionAttributableToNoncontrollingInterestOfWhollyOwnedIndirectSubsidiaryOfRegistrant_b5bb5ee4-476c-44fb-827a-dd1d35983778" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_7af6b486-1a09-46d4-8a00-c509181db693" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_786cc78a-5382-4905-bf3c-eecb55f753be" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_7af6b486-1a09-46d4-8a00-c509181db693" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_6458674d-59a5-4b9b-9836-fbf115794195" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_713bf7f7-7569-40a5-b27f-fe9fc7799b3f" xlink:to="loc_us-gaap_StatementTable_6458674d-59a5-4b9b-9836-fbf115794195" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_852687d2-cebb-4a92-a33d-9fb20cbf414c" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6458674d-59a5-4b9b-9836-fbf115794195" xlink:to="loc_dei_LegalEntityAxis_852687d2-cebb-4a92-a33d-9fb20cbf414c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_852687d2-cebb-4a92-a33d-9fb20cbf414c_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_852687d2-cebb-4a92-a33d-9fb20cbf414c" xlink:to="loc_dei_EntityDomain_852687d2-cebb-4a92-a33d-9fb20cbf414c_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_ade049db-05f1-4336-8a87-95104c7a2339" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_852687d2-cebb-4a92-a33d-9fb20cbf414c" xlink:to="loc_dei_EntityDomain_ade049db-05f1-4336-8a87-95104c7a2339" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_393454f7-7ee0-483f-82d0-1c5c5ae0d2ee" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_ade049db-05f1-4336-8a87-95104c7a2339" xlink:to="loc_sum_SummitMaterialsLlcMember_393454f7-7ee0-483f-82d0-1c5c5ae0d2ee" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/UnauditedConsolidatedStatementsofCashFlows" xlink:type="simple" xlink:href="sum-20220702.xsd#UnauditedConsolidatedStatementsofCashFlows"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/UnauditedConsolidatedStatementsofCashFlows" xlink:type="extended" id="if177cd114661436b87ad3704485d335c_UnauditedConsolidatedStatementsofCashFlows">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_c5fdc47a-f6b4-4195-b0db-6e2d9de7ecf4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_75c9ec88-c521-41be-96a3-db8a244b5ce4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5fdc47a-f6b4-4195-b0db-6e2d9de7ecf4" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_75c9ec88-c521-41be-96a3-db8a244b5ce4" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_9b6c4967-3b0e-40f5-969b-edf7d9b2c3fe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProfitLoss"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_75c9ec88-c521-41be-96a3-db8a244b5ce4" xlink:to="loc_us-gaap_ProfitLoss_9b6c4967-3b0e-40f5-969b-edf7d9b2c3fe" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ccb3cf33-281a-4542-9d7c-b37d8f65c731" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_75c9ec88-c521-41be-96a3-db8a244b5ce4" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ccb3cf33-281a-4542-9d7c-b37d8f65c731" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_DepreciationDepletionAmortizationAndAccretionOnAssetRetirementObligation_86682619-4423-4281-85d1-3d1dcca7b2a4" xlink:href="sum-20220702.xsd#sum_DepreciationDepletionAmortizationAndAccretionOnAssetRetirementObligation"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ccb3cf33-281a-4542-9d7c-b37d8f65c731" xlink:to="loc_sum_DepreciationDepletionAmortizationAndAccretionOnAssetRetirementObligation_86682619-4423-4281-85d1-3d1dcca7b2a4" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_34749e7d-4db6-4186-88cc-ac8ce36542b9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensation"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ccb3cf33-281a-4542-9d7c-b37d8f65c731" xlink:to="loc_us-gaap_ShareBasedCompensation_34749e7d-4db6-4186-88cc-ac8ce36542b9" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfAssets1_5cc8a08f-ae02-4d8c-9f2e-b65589b82d59" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainLossOnDispositionOfAssets1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ccb3cf33-281a-4542-9d7c-b37d8f65c731" xlink:to="loc_us-gaap_GainLossOnDispositionOfAssets1_5cc8a08f-ae02-4d8c-9f2e-b65589b82d59" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxesAndTaxCredits_b7537320-7cad-44c9-98e5-0a71913ef9c8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredIncomeTaxesAndTaxCredits"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ccb3cf33-281a-4542-9d7c-b37d8f65c731" xlink:to="loc_us-gaap_DeferredIncomeTaxesAndTaxCredits_b7537320-7cad-44c9-98e5-0a71913ef9c8" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncashIncomeExpense_b9c735fe-1004-4a27-820d-c026a3407899" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherNoncashIncomeExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ccb3cf33-281a-4542-9d7c-b37d8f65c731" xlink:to="loc_us-gaap_OtherNoncashIncomeExpense_b9c735fe-1004-4a27-820d-c026a3407899" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_9f2bbb38-b4f9-4d25-955f-e5f0b5a392f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOperatingAssetsAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_ccb3cf33-281a-4542-9d7c-b37d8f65c731" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_9f2bbb38-b4f9-4d25-955f-e5f0b5a392f3" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_01810c56-5d66-4e56-9b99-259b601adcba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_9f2bbb38-b4f9-4d25-955f-e5f0b5a392f3" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_01810c56-5d66-4e56-9b99-259b601adcba" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_d11fbda0-4586-4930-9c85-f755f8622d57" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInInventories"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_9f2bbb38-b4f9-4d25-955f-e5f0b5a392f3" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_d11fbda0-4586-4930-9c85-f755f8622d57" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ContractWithCustomerAssetCumulativeCatchupAdjustmentToRevenueChangeInRevenueBilledContractPriceOrEstimates_578336c5-6e3f-4564-8f82-3999846538d0" xlink:href="sum-20220702.xsd#sum_ContractWithCustomerAssetCumulativeCatchupAdjustmentToRevenueChangeInRevenueBilledContractPriceOrEstimates"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_9f2bbb38-b4f9-4d25-955f-e5f0b5a392f3" xlink:to="loc_sum_ContractWithCustomerAssetCumulativeCatchupAdjustmentToRevenueChangeInRevenueBilledContractPriceOrEstimates_578336c5-6e3f-4564-8f82-3999846538d0" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherCurrentAssets_ede74d0c-47ca-4b42-ae5d-8082a35cf5f2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOtherCurrentAssets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_9f2bbb38-b4f9-4d25-955f-e5f0b5a392f3" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherCurrentAssets_ede74d0c-47ca-4b42-ae5d-8082a35cf5f2" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_fd207f57-4d60-4716-b76b-142e5b8092de" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentAssets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_9f2bbb38-b4f9-4d25-955f-e5f0b5a392f3" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_fd207f57-4d60-4716-b76b-142e5b8092de" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_b5d097f6-84c5-4992-8df4-81bdc2459e2e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingAssetsAbstract_9f2bbb38-b4f9-4d25-955f-e5f0b5a392f3" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_b5d097f6-84c5-4992-8df4-81bdc2459e2e" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_8329927b-5c44-45b4-82bc-05d0b6a47d58" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_b5d097f6-84c5-4992-8df4-81bdc2459e2e" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_8329927b-5c44-45b4-82bc-05d0b6a47d58" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_76da940c-555a-4e14-b96b-994b22fa89e8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_b5d097f6-84c5-4992-8df4-81bdc2459e2e" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_76da940c-555a-4e14-b96b-994b22fa89e8" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ContractWithCustomerLiabilityCumulativeCatchupAdjustmentToRevenueChangeInRevenueBilledContractPriceOrCostEstimates_468cf107-97d9-442a-bf1e-0cb2d813bf0f" xlink:href="sum-20220702.xsd#sum_ContractWithCustomerLiabilityCumulativeCatchupAdjustmentToRevenueChangeInRevenueBilledContractPriceOrCostEstimates"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_b5d097f6-84c5-4992-8df4-81bdc2459e2e" xlink:to="loc_sum_ContractWithCustomerLiabilityCumulativeCatchupAdjustmentToRevenueChangeInRevenueBilledContractPriceOrCostEstimates_468cf107-97d9-442a-bf1e-0cb2d813bf0f" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_IncreaseDecreaseInTaxReceivableAgreementLiability_d6d3c474-c035-4fdd-b40e-942723aa86a8" xlink:href="sum-20220702.xsd#sum_IncreaseDecreaseInTaxReceivableAgreementLiability"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_b5d097f6-84c5-4992-8df4-81bdc2459e2e" xlink:to="loc_sum_IncreaseDecreaseInTaxReceivableAgreementLiability_d6d3c474-c035-4fdd-b40e-942723aa86a8" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3d94fcdf-8374-4636-8658-718f2e97acbe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOtherOperatingLiabilities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingLiabilitiesAbstract_b5d097f6-84c5-4992-8df4-81bdc2459e2e" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3d94fcdf-8374-4636-8658-718f2e97acbe" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_dfb802d9-cf03-4aac-8a0f-b399d25de62d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_75c9ec88-c521-41be-96a3-db8a244b5ce4" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_dfb802d9-cf03-4aac-8a0f-b399d25de62d" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_579d8614-6167-47bf-9b5c-ce10971c5618" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5fdc47a-f6b4-4195-b0db-6e2d9de7ecf4" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_579d8614-6167-47bf-9b5c-ce10971c5618" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_bff7e5e6-58b9-4865-85d2-dbeadeb476f8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_579d8614-6167-47bf-9b5c-ce10971c5618" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_bff7e5e6-58b9-4865-85d2-dbeadeb476f8" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_4a399759-b3c9-49b2-a30f-d94447181808" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_579d8614-6167-47bf-9b5c-ce10971c5618" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_4a399759-b3c9-49b2-a30f-d94447181808" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_31c25dc6-544e-4a35-9acb-f67750037850" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_579d8614-6167-47bf-9b5c-ce10971c5618" xlink:to="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_31c25dc6-544e-4a35-9acb-f67750037850" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_71e5f117-3a65-4ec1-8897-18160e31d309" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_579d8614-6167-47bf-9b5c-ce10971c5618" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_71e5f117-3a65-4ec1-8897-18160e31d309" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_2d136391-e51e-44e8-9e08-cbfe433068c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_579d8614-6167-47bf-9b5c-ce10971c5618" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_2d136391-e51e-44e8-9e08-cbfe433068c3" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_2dfe1773-0715-4edf-8256-d6d17ad5619c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_579d8614-6167-47bf-9b5c-ce10971c5618" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_2dfe1773-0715-4edf-8256-d6d17ad5619c" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_0053e1a9-d34f-4c22-9041-852625a3e050" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5fdc47a-f6b4-4195-b0db-6e2d9de7ecf4" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_0053e1a9-d34f-4c22-9041-852625a3e050" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ProceedsFromPaymentsForPartnershipContribution_c37ac5ea-a595-4231-a9c1-3940d4ba44c8" xlink:href="sum-20220702.xsd#sum_ProceedsFromPaymentsForPartnershipContribution"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_0053e1a9-d34f-4c22-9041-852625a3e050" xlink:to="loc_sum_ProceedsFromPaymentsForPartnershipContribution_c37ac5ea-a595-4231-a9c1-3940d4ba44c8" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfDebt_01da4e41-ac97-4729-85d4-ba138757861b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_0053e1a9-d34f-4c22-9041-852625a3e050" xlink:to="loc_us-gaap_RepaymentsOfDebt_01da4e41-ac97-4729-85d4-ba138757861b" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfMergerRelatedCostsFinancingActivities_c7c1e776-f551-4fbc-9dc5-8eb032bb0df5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfMergerRelatedCostsFinancingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_0053e1a9-d34f-4c22-9041-852625a3e050" xlink:to="loc_us-gaap_PaymentsOfMergerRelatedCostsFinancingActivities_c7c1e776-f551-4fbc-9dc5-8eb032bb0df5" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDistributionsToAffiliates_49514720-5a67-49ab-a38a-41d875b14969" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfDistributionsToAffiliates"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_0053e1a9-d34f-4c22-9041-852625a3e050" xlink:to="loc_us-gaap_PaymentsOfDistributionsToAffiliates_49514720-5a67-49ab-a38a-41d875b14969" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_2f374991-7beb-4d20-8853-a36810e7d005" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_0053e1a9-d34f-4c22-9041-852625a3e050" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_2f374991-7beb-4d20-8853-a36810e7d005" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockOptionsExercised_7dad293d-9834-4e0a-8d1d-d8d92304c639" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromStockOptionsExercised"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_0053e1a9-d34f-4c22-9041-852625a3e050" xlink:to="loc_us-gaap_ProceedsFromStockOptionsExercised_7dad293d-9834-4e0a-8d1d-d8d92304c639" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_6bcf709c-c872-4f69-a718-a5ead6eef232" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_0053e1a9-d34f-4c22-9041-852625a3e050" xlink:to="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_6bcf709c-c872-4f69-a718-a5ead6eef232" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7c463657-49bb-4372-b623-496bea4c9f22" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_0053e1a9-d34f-4c22-9041-852625a3e050" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_7c463657-49bb-4372-b623-496bea4c9f22" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_72f0991e-1cf3-40f1-9f7b-ded7bfa95255" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5fdc47a-f6b4-4195-b0db-6e2d9de7ecf4" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_72f0991e-1cf3-40f1-9f7b-ded7bfa95255" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_d3e619f6-da67-4e57-a27b-5f00550841d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5fdc47a-f6b4-4195-b0db-6e2d9de7ecf4" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_d3e619f6-da67-4e57-a27b-5f00550841d2" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_9f5c840f-adde-4fd0-8f71-0c63a009a5af" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_c5fdc47a-f6b4-4195-b0db-6e2d9de7ecf4" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_9f5c840f-adde-4fd0-8f71-0c63a009a5af" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_9f1143fe-d89d-4700-95f1-c6f30cd66b5e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_8894a8fa-1cde-42a1-994e-b14c4309e13d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_c5fdc47a-f6b4-4195-b0db-6e2d9de7ecf4" xlink:to="loc_us-gaap_StatementTable_8894a8fa-1cde-42a1-994e-b14c4309e13d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_1bc080f6-a344-4671-87e6-ee6d399b02d9" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8894a8fa-1cde-42a1-994e-b14c4309e13d" xlink:to="loc_dei_LegalEntityAxis_1bc080f6-a344-4671-87e6-ee6d399b02d9" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_1bc080f6-a344-4671-87e6-ee6d399b02d9_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1bc080f6-a344-4671-87e6-ee6d399b02d9" xlink:to="loc_dei_EntityDomain_1bc080f6-a344-4671-87e6-ee6d399b02d9_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_adbbcb04-7c62-420e-835d-e13e71110db1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1bc080f6-a344-4671-87e6-ee6d399b02d9" xlink:to="loc_dei_EntityDomain_adbbcb04-7c62-420e-835d-e13e71110db1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_8d0a0a70-73a2-44be-b716-e6d5d9dc9acc" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_adbbcb04-7c62-420e-835d-e13e71110db1" xlink:to="loc_sum_SummitMaterialsLlcMember_8d0a0a70-73a2-44be-b716-e6d5d9dc9acc" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/UnauditedConsolidatedStatementsofChangesinStockholdersEquityMembersInterest" xlink:type="simple" xlink:href="sum-20220702.xsd#UnauditedConsolidatedStatementsofChangesinStockholdersEquityMembersInterest"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/UnauditedConsolidatedStatementsofChangesinStockholdersEquityMembersInterest" xlink:type="extended" id="i0faafd16c6d64614bd45f9fcfa94c532_UnauditedConsolidatedStatementsofChangesinStockholdersEquityMembersInterest">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_259fbb46-b965-4797-b0a5-5f7df018e238" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_259fbb46-b965-4797-b0a5-5f7df018e238" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_6c0dcd20-0675-4e8c-adde-3b067c9e1ff1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_6c0dcd20-0675-4e8c-adde-3b067c9e1ff1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_6db05e0f-7b10-4e1c-a613-cfa69cfb1549" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_6db05e0f-7b10-4e1c-a613-cfa69cfb1549" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_3c0091b9-10af-4503-bd36-9c1483608fad" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_CommonStockSharesIssued_3c0091b9-10af-4503-bd36-9c1483608fad" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ContributionToMembersEquity_1e99379b-4a07-4974-ae71-a580e121b076" xlink:href="sum-20220702.xsd#sum_ContributionToMembersEquity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_sum_ContributionToMembersEquity_1e99379b-4a07-4974-ae71-a580e121b076" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_ae5f3244-d16a-41dc-9c6e-181852f1314f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProfitLoss"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_ProfitLoss_ae5f3244-d16a-41dc-9c6e-181852f1314f" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_2a761dbb-039a-4488-aebb-ba9fc3dac6f6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_2a761dbb-039a-4488-aebb-ba9fc3dac6f6" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_94cc6b45-fe2a-4358-a4e1-f1c6097ee1b7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfUnits"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfUnits_94cc6b45-fe2a-4358-a4e1-f1c6097ee1b7" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_9fbd60ae-26ac-40a0-9bb7-dadefb58310b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_9fbd60ae-26ac-40a0-9bb7-dadefb58310b" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DistributionMadeToLimitedLiabilityCompanyLLCMemberCashDistributionsDeclared_27db21e1-46ea-41cc-bff4-616b53c24ac1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DistributionMadeToLimitedLiabilityCompanyLLCMemberCashDistributionsDeclared"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_DistributionMadeToLimitedLiabilityCompanyLLCMemberCashDistributionsDeclared_27db21e1-46ea-41cc-bff4-616b53c24ac1" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_1cd8cbca-8898-4142-a8b9-299ca9e81b79" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_1cd8cbca-8898-4142-a8b9-299ca9e81b79" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_db0ecbce-334d-430d-b1d4-4bde835e74fe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_db0ecbce-334d-430d-b1d4-4bde835e74fe" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_0fd1b2a5-f8a3-4aec-b5d9-6040c9b793ec" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_0fd1b2a5-f8a3-4aec-b5d9-6040c9b793ec" xlink:type="arc" order="12"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_8c0e3505-f27b-4142-bbac-e1f443b9de89" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_8c0e3505-f27b-4142-bbac-e1f443b9de89" xlink:type="arc" order="13"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_e23cc055-f97a-455d-9098-8d0c218f5961" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_e23cc055-f97a-455d-9098-8d0c218f5961" xlink:type="arc" order="14"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PartnersCapitalAccountDistributions_c1999e6c-ed11-4f2f-b382-801a05b9a20c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PartnersCapitalAccountDistributions"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_us-gaap_PartnersCapitalAccountDistributions_c1999e6c-ed11-4f2f-b382-801a05b9a20c" xlink:type="arc" order="15"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_OtherEquityActivityShares_7a43af1f-31c6-434e-a82b-26577371350a" xlink:href="sum-20220702.xsd#sum_OtherEquityActivityShares"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_sum_OtherEquityActivityShares_7a43af1f-31c6-434e-a82b-26577371350a" xlink:type="arc" order="16"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_OtherEquityActivityValue_b06dc338-5550-4b4f-a080-f69d57ec3a17" xlink:href="sum-20220702.xsd#sum_OtherEquityActivityValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_3ccc41a2-c567-4757-95b8-41403017cf4b" xlink:to="loc_sum_OtherEquityActivityValue_b06dc338-5550-4b4f-a080-f69d57ec3a17" xlink:type="arc" order="17"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_77c45a83-0821-4960-b991-4102def4904f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_c09a3340-bb64-41a8-948a-e2cc23453cba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_de2588ee-df46-4413-a886-30e22689c82b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_f2491582-ae4d-417e-bb80-4b5f9dc2882f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_259fbb46-b965-4797-b0a5-5f7df018e238" xlink:to="loc_us-gaap_StatementTable_f2491582-ae4d-417e-bb80-4b5f9dc2882f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_91500f35-032b-4ab2-a3c6-5eef44376443" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_f2491582-ae4d-417e-bb80-4b5f9dc2882f" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_91500f35-032b-4ab2-a3c6-5eef44376443" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_91500f35-032b-4ab2-a3c6-5eef44376443_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_91500f35-032b-4ab2-a3c6-5eef44376443" xlink:to="loc_us-gaap_EquityComponentDomain_91500f35-032b-4ab2-a3c6-5eef44376443_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_50bdd8e8-2d3e-4a47-84bf-d425416981a5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_91500f35-032b-4ab2-a3c6-5eef44376443" xlink:to="loc_us-gaap_EquityComponentDomain_50bdd8e8-2d3e-4a47-84bf-d425416981a5" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_MemberUnitsMember_02b91149-340c-4e6e-bee5-efbfba09fc61" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MemberUnitsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50bdd8e8-2d3e-4a47-84bf-d425416981a5" xlink:to="loc_us-gaap_MemberUnitsMember_02b91149-340c-4e6e-bee5-efbfba09fc61" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_8b776bd7-df46-45c8-8d08-76cbcb5cb6f5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50bdd8e8-2d3e-4a47-84bf-d425416981a5" xlink:to="loc_us-gaap_RetainedEarningsMember_8b776bd7-df46-45c8-8d08-76cbcb5cb6f5" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_a3233382-de0e-43e9-a356-0f8b746501ed" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50bdd8e8-2d3e-4a47-84bf-d425416981a5" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_a3233382-de0e-43e9-a356-0f8b746501ed" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_647f2fb7-e972-49b1-911d-8f5a9d2fa237" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50bdd8e8-2d3e-4a47-84bf-d425416981a5" xlink:to="loc_us-gaap_CommonStockMember_647f2fb7-e972-49b1-911d-8f5a9d2fa237" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_e02e229d-7be7-435a-89f2-3659fc211bac" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50bdd8e8-2d3e-4a47-84bf-d425416981a5" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_e02e229d-7be7-435a-89f2-3659fc211bac" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_NoncontrollingInterestInLpMember_872c3c5d-89de-4a5a-a926-55925e3b3d1a" xlink:href="sum-20220702.xsd#sum_NoncontrollingInterestInLpMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50bdd8e8-2d3e-4a47-84bf-d425416981a5" xlink:to="loc_sum_NoncontrollingInterestInLpMember_872c3c5d-89de-4a5a-a926-55925e3b3d1a" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_a6a25903-18d8-4f96-b0bb-22e6f7f341a2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_f2491582-ae4d-417e-bb80-4b5f9dc2882f" xlink:to="loc_us-gaap_StatementClassOfStockAxis_a6a25903-18d8-4f96-b0bb-22e6f7f341a2" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_a6a25903-18d8-4f96-b0bb-22e6f7f341a2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_a6a25903-18d8-4f96-b0bb-22e6f7f341a2" xlink:to="loc_us-gaap_ClassOfStockDomain_a6a25903-18d8-4f96-b0bb-22e6f7f341a2_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_4972756b-8696-42d2-8a0c-04df448b0556" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_a6a25903-18d8-4f96-b0bb-22e6f7f341a2" xlink:to="loc_us-gaap_ClassOfStockDomain_4972756b-8696-42d2-8a0c-04df448b0556" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_9182b278-f549-4732-b3a1-176d138d84c7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_4972756b-8696-42d2-8a0c-04df448b0556" xlink:to="loc_us-gaap_CommonClassAMember_9182b278-f549-4732-b3a1-176d138d84c7" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_a93373b9-cd9e-4d98-a26f-1719bbe74665" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassBMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_4972756b-8696-42d2-8a0c-04df448b0556" xlink:to="loc_us-gaap_CommonClassBMember_a93373b9-cd9e-4d98-a26f-1719bbe74665" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_1c52257b-b0bc-44e5-adf0-38e0132449ce" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_f2491582-ae4d-417e-bb80-4b5f9dc2882f" xlink:to="loc_dei_LegalEntityAxis_1c52257b-b0bc-44e5-adf0-38e0132449ce" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_1c52257b-b0bc-44e5-adf0-38e0132449ce_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1c52257b-b0bc-44e5-adf0-38e0132449ce" xlink:to="loc_dei_EntityDomain_1c52257b-b0bc-44e5-adf0-38e0132449ce_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_510f6b39-bf77-49d5-99ac-843434ce9fe7" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1c52257b-b0bc-44e5-adf0-38e0132449ce" xlink:to="loc_dei_EntityDomain_510f6b39-bf77-49d5-99ac-843434ce9fe7" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_b9ba864b-c280-4b01-a190-e2f37329b06d" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_510f6b39-bf77-49d5-99ac-843434ce9fe7" xlink:to="loc_sum_SummitMaterialsLlcMember_b9ba864b-c280-4b01-a190-e2f37329b06d" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIES" xlink:type="simple" xlink:href="sum-20220702.xsd#SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIES"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIES" xlink:type="extended" id="i072f48784d9a4c7dadef9d2b614c64e2_SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIES">
<link:loc xlink:type="locator" xlink:label="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_6c855388-2625-4608-af28-e1a526c4b33e" xlink:href="sum-20220702.xsd#sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OrganizationConsolidationBasisOfPresentationBusinessDescriptionAndAccountingPoliciesTextBlock_eeed7900-46e9-4911-ae41-a061e28d89b2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OrganizationConsolidationBasisOfPresentationBusinessDescriptionAndAccountingPoliciesTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_6c855388-2625-4608-af28-e1a526c4b33e" xlink:to="loc_us-gaap_OrganizationConsolidationBasisOfPresentationBusinessDescriptionAndAccountingPoliciesTextBlock_eeed7900-46e9-4911-ae41-a061e28d89b2" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable_dbd725bd-e362-4ee7-b638-5ce89704f3ed" xlink:href="sum-20220702.xsd#sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_6c855388-2625-4608-af28-e1a526c4b33e" xlink:to="loc_sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable_dbd725bd-e362-4ee7-b638-5ce89704f3ed" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_647e639e-25a7-47a5-81d7-e236221b2f07" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable_dbd725bd-e362-4ee7-b638-5ce89704f3ed" xlink:to="loc_dei_LegalEntityAxis_647e639e-25a7-47a5-81d7-e236221b2f07" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_647e639e-25a7-47a5-81d7-e236221b2f07_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_647e639e-25a7-47a5-81d7-e236221b2f07" xlink:to="loc_dei_EntityDomain_647e639e-25a7-47a5-81d7-e236221b2f07_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_3ce87b5b-07ca-40b9-9370-558979816731" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_647e639e-25a7-47a5-81d7-e236221b2f07" xlink:to="loc_dei_EntityDomain_3ce87b5b-07ca-40b9-9370-558979816731" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_c4c6d576-532c-416e-b2c5-e2cfd0690ffa" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3ce87b5b-07ca-40b9-9370-558979816731" xlink:to="loc_sum_SummitMaterialsLlcMember_c4c6d576-532c-416e-b2c5-e2cfd0690ffa" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESPolicies" xlink:type="simple" xlink:href="sum-20220702.xsd#SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESPolicies"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESPolicies" xlink:type="extended" id="ifde11e8272d24ef88ed46396a9111b78_SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESPolicies">
<link:loc xlink:type="locator" xlink:label="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_35f73e8e-702c-4aba-b354-932fa4bd22b2" xlink:href="sum-20220702.xsd#sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_bc3314a2-bb7b-49e5-80df-d8e797b4d584" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_35f73e8e-702c-4aba-b354-932fa4bd22b2" xlink:to="loc_us-gaap_BasisOfAccountingPolicyPolicyTextBlock_bc3314a2-bb7b-49e5-80df-d8e797b4d584" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsolidationPolicyTextBlock_0b1c6ba4-d496-4b14-996d-94cc3c4a502f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsolidationPolicyTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_35f73e8e-702c-4aba-b354-932fa4bd22b2" xlink:to="loc_us-gaap_ConsolidationPolicyTextBlock_0b1c6ba4-d496-4b14-996d-94cc3c4a502f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_UseOfEstimates_60c632fe-c3b1-4773-995a-2ca0736bfb1d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UseOfEstimates"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_35f73e8e-702c-4aba-b354-932fa4bd22b2" xlink:to="loc_us-gaap_UseOfEstimates_60c632fe-c3b1-4773-995a-2ca0736bfb1d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskCreditRisk_ceed2bd4-ba34-457b-a3a1-bb26466654e1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskCreditRisk"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_35f73e8e-702c-4aba-b354-932fa4bd22b2" xlink:to="loc_us-gaap_ConcentrationRiskCreditRisk_ceed2bd4-ba34-457b-a3a1-bb26466654e1" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerPolicyTextBlock_7922de84-5073-4634-bc8a-c42b36c05ca0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerPolicyTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_35f73e8e-702c-4aba-b354-932fa4bd22b2" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerPolicyTextBlock_7922de84-5073-4634-bc8a-c42b36c05ca0" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerSharePolicyTextBlock_71e1586b-68e2-40f6-9a74-a33c13fb73e7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerSharePolicyTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_35f73e8e-702c-4aba-b354-932fa4bd22b2" xlink:to="loc_us-gaap_EarningsPerSharePolicyTextBlock_71e1586b-68e2-40f6-9a74-a33c13fb73e7" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PriorPeriodReclassificationAdjustmentDescription_b5c4158b-c0a7-49e7-a4c8-8e4d571be065" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PriorPeriodReclassificationAdjustmentDescription"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_35f73e8e-702c-4aba-b354-932fa4bd22b2" xlink:to="loc_us-gaap_PriorPeriodReclassificationAdjustmentDescription_b5c4158b-c0a7-49e7-a4c8-8e4d571be065" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeasesPolicyTextBlock_fea3ad9e-b223-4a4b-bea0-46e60c86f941" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeasesPolicyTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_35f73e8e-702c-4aba-b354-932fa4bd22b2" xlink:to="loc_us-gaap_LesseeLeasesPolicyTextBlock_fea3ad9e-b223-4a4b-bea0-46e60c86f941" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable_7791cce2-a369-4767-a7f8-0d4fae1ba439" xlink:href="sum-20220702.xsd#sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_35f73e8e-702c-4aba-b354-932fa4bd22b2" xlink:to="loc_sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable_7791cce2-a369-4767-a7f8-0d4fae1ba439" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a40eb596-6da2-4783-bef4-e088c980da07" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable_7791cce2-a369-4767-a7f8-0d4fae1ba439" xlink:to="loc_dei_LegalEntityAxis_a40eb596-6da2-4783-bef4-e088c980da07" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a40eb596-6da2-4783-bef4-e088c980da07_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a40eb596-6da2-4783-bef4-e088c980da07" xlink:to="loc_dei_EntityDomain_a40eb596-6da2-4783-bef4-e088c980da07_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_ef123529-c188-4106-a201-1d93e2f05502" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a40eb596-6da2-4783-bef4-e088c980da07" xlink:to="loc_dei_EntityDomain_ef123529-c188-4106-a201-1d93e2f05502" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_bc04b90f-fce2-430a-b008-2f094f2eff2d" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_ef123529-c188-4106-a201-1d93e2f05502" xlink:to="loc_sum_SummitMaterialsLlcMember_bc04b90f-fce2-430a-b008-2f094f2eff2d" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESGeneralInformationDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESGeneralInformationDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESGeneralInformationDetails" xlink:type="extended" id="i448afdcdb6d44cd688aaa0cbdf4b2c3e_SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESGeneralInformationDetails">
<link:loc xlink:type="locator" xlink:label="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_988bcf2c-f5b6-48e3-8f76-bd24f17d8133" xlink:href="sum-20220702.xsd#sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_NumberOfPlantsOwnedAndOperated_f4a02a95-04bf-4aeb-ab66-93c12a7d7f9b" xlink:href="sum-20220702.xsd#sum_NumberOfPlantsOwnedAndOperated"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_988bcf2c-f5b6-48e3-8f76-bd24f17d8133" xlink:to="loc_sum_NumberOfPlantsOwnedAndOperated_f4a02a95-04bf-4aeb-ab66-93c12a7d7f9b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_c80d0ec0-124b-4a59-a98e-8f3902b9baff" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfOperatingSegments"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_988bcf2c-f5b6-48e3-8f76-bd24f17d8133" xlink:to="loc_us-gaap_NumberOfOperatingSegments_c80d0ec0-124b-4a59-a98e-8f3902b9baff" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_dac8b1d5-a14b-4f65-a7cb-30d3f624b800" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfReportableSegments"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_988bcf2c-f5b6-48e3-8f76-bd24f17d8133" xlink:to="loc_us-gaap_NumberOfReportableSegments_dac8b1d5-a14b-4f65-a7cb-30d3f624b800" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable_d82b50a0-ff61-419e-b1db-83598355a370" xlink:href="sum-20220702.xsd#sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsLineItems_988bcf2c-f5b6-48e3-8f76-bd24f17d8133" xlink:to="loc_sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable_d82b50a0-ff61-419e-b1db-83598355a370" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_5fc68da0-31e9-4986-a3ee-999de23f11a7" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable_d82b50a0-ff61-419e-b1db-83598355a370" xlink:to="loc_dei_LegalEntityAxis_5fc68da0-31e9-4986-a3ee-999de23f11a7" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5fc68da0-31e9-4986-a3ee-999de23f11a7_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_5fc68da0-31e9-4986-a3ee-999de23f11a7" xlink:to="loc_dei_EntityDomain_5fc68da0-31e9-4986-a3ee-999de23f11a7_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e5303fed-9770-45d0-a39a-522206e595b8" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_5fc68da0-31e9-4986-a3ee-999de23f11a7" xlink:to="loc_dei_EntityDomain_e5303fed-9770-45d0-a39a-522206e595b8" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_e214f3a4-a938-4e43-a5e1-4e2e2ef2b8b4" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_e5303fed-9770-45d0-a39a-522206e595b8" xlink:to="loc_sum_SummitMaterialsLlcMember_e214f3a4-a938-4e43-a5e1-4e2e2ef2b8b4" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_feda755c-40ea-4e2e-98f6-27f6c3c09556" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_ScheduleOfSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTable_d82b50a0-ff61-419e-b1db-83598355a370" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_feda755c-40ea-4e2e-98f6-27f6c3c09556" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_feda755c-40ea-4e2e-98f6-27f6c3c09556_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_feda755c-40ea-4e2e-98f6-27f6c3c09556" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_feda755c-40ea-4e2e-98f6-27f6c3c09556_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_0f736216-2687-4269-bdf4-a7c08d622e99" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_feda755c-40ea-4e2e-98f6-27f6c3c09556" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_0f736216-2687-4269-bdf4-a7c08d622e99" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CementPlantMember_da4b43b8-54bb-4f65-b354-b5142df0bbaf" xlink:href="sum-20220702.xsd#sum_CementPlantMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_0f736216-2687-4269-bdf4-a7c08d622e99" xlink:to="loc_sum_CementPlantMember_da4b43b8-54bb-4f65-b354-b5142df0bbaf" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESBusinessandCreditConcentrationTaxReceivableAgreementDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESBusinessandCreditConcentrationTaxReceivableAgreementDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESBusinessandCreditConcentrationTaxReceivableAgreementDetails" xlink:type="extended" id="ic7f2fb0fb37b4662b907e59a960f77c7_SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESBusinessandCreditConcentrationTaxReceivableAgreementDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_97a924a5-c3c4-44fe-a169-777db0b81ba5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfStatesInWhichEntityOperates_ca2aa888-bf5d-4ae4-ace1-e5ef9cda51f9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfStatesInWhichEntityOperates"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_97a924a5-c3c4-44fe-a169-777db0b81ba5" xlink:to="loc_us-gaap_NumberOfStatesInWhichEntityOperates_ca2aa888-bf5d-4ae4-ace1-e5ef9cda51f9" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_3d59566a-3311-4027-a5a2-c14676f847af" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConcentrationRiskTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_97a924a5-c3c4-44fe-a169-777db0b81ba5" xlink:to="loc_us-gaap_ConcentrationRiskTable_3d59566a-3311-4027-a5a2-c14676f847af" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a3bafde2-d09c-4276-8f93-694538c53821" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_3d59566a-3311-4027-a5a2-c14676f847af" xlink:to="loc_dei_LegalEntityAxis_a3bafde2-d09c-4276-8f93-694538c53821" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a3bafde2-d09c-4276-8f93-694538c53821_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a3bafde2-d09c-4276-8f93-694538c53821" xlink:to="loc_dei_EntityDomain_a3bafde2-d09c-4276-8f93-694538c53821_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_63819a8d-55f1-4120-b28f-264de27ecee5" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a3bafde2-d09c-4276-8f93-694538c53821" xlink:to="loc_dei_EntityDomain_63819a8d-55f1-4120-b28f-264de27ecee5" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_72b8199e-71e2-4937-9150-9cb5b06f1b20" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_63819a8d-55f1-4120-b28f-264de27ecee5" xlink:to="loc_sum_SummitMaterialsLlcMember_72b8199e-71e2-4937-9150-9cb5b06f1b20" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESPriorPeriodReclassificationsDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESPriorPeriodReclassificationsDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESPriorPeriodReclassificationsDetails" xlink:type="extended" id="i94918373e7314e399311c58e11e93955_SUMMARYOFORGANIZATIONANDSIGNIFICANTACCOUNTINGPOLICIESPriorPeriodReclassificationsDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationLineItems_23c780c7-b19f-48b3-b5b4-6dfb1bb930bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ReclassificationLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_OtherAssetsReclassifiedToAssetsHeldForSaleCurrent_e50c9de4-69b9-4acb-9ec0-c5fa9566cad7" xlink:href="sum-20220702.xsd#sum_OtherAssetsReclassifiedToAssetsHeldForSaleCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationLineItems_23c780c7-b19f-48b3-b5b4-6dfb1bb930bf" xlink:to="loc_sum_OtherAssetsReclassifiedToAssetsHeldForSaleCurrent_e50c9de4-69b9-4acb-9ec0-c5fa9566cad7" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationTable_5ba5e3e7-f547-4bed-8df5-0d0d717e6bca" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ReclassificationTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReclassificationLineItems_23c780c7-b19f-48b3-b5b4-6dfb1bb930bf" xlink:to="loc_us-gaap_ReclassificationTable_5ba5e3e7-f547-4bed-8df5-0d0d717e6bca" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_f4e77b91-a50a-4391-b744-61b2ecf6318b" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationTable_5ba5e3e7-f547-4bed-8df5-0d0d717e6bca" xlink:to="loc_dei_LegalEntityAxis_f4e77b91-a50a-4391-b744-61b2ecf6318b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f4e77b91-a50a-4391-b744-61b2ecf6318b_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_f4e77b91-a50a-4391-b744-61b2ecf6318b" xlink:to="loc_dei_EntityDomain_f4e77b91-a50a-4391-b744-61b2ecf6318b_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_9b7d2076-52cb-41de-bf1a-e31594874829" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_f4e77b91-a50a-4391-b744-61b2ecf6318b" xlink:to="loc_dei_EntityDomain_9b7d2076-52cb-41de-bf1a-e31594874829" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_fb39547a-5f11-4ad3-b0ac-b8d01c01cccb" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_9b7d2076-52cb-41de-bf1a-e31594874829" xlink:to="loc_sum_SummitMaterialsLlcMember_fb39547a-5f11-4ad3-b0ac-b8d01c01cccb" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_8f32fde0-a438-44b6-abf9-d2d4be4af236" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationTable_5ba5e3e7-f547-4bed-8df5-0d0d717e6bca" xlink:to="loc_srt_RestatementAxis_8f32fde0-a438-44b6-abf9-d2d4be4af236" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_8f32fde0-a438-44b6-abf9-d2d4be4af236_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_8f32fde0-a438-44b6-abf9-d2d4be4af236" xlink:to="loc_srt_RestatementDomain_8f32fde0-a438-44b6-abf9-d2d4be4af236_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_3bfd4dde-c04f-4afa-afde-1755916a05c8" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RestatementDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_8f32fde0-a438-44b6-abf9-d2d4be4af236" xlink:to="loc_srt_RestatementDomain_3bfd4dde-c04f-4afa-afde-1755916a05c8" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RevisionOfPriorPeriodReclassificationAdjustmentMember_d7d77900-a948-4c5d-8e47-740b0549a1f4" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RevisionOfPriorPeriodReclassificationAdjustmentMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_3bfd4dde-c04f-4afa-afde-1755916a05c8" xlink:to="loc_srt_RevisionOfPriorPeriodReclassificationAdjustmentMember_d7d77900-a948-4c5d-8e47-740b0549a1f4" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLES" xlink:type="simple" xlink:href="sum-20220702.xsd#ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLES"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLES" xlink:type="extended" id="icd957051e7d04a0493987f1b1ae6985c_ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLES">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_dcb5b50c-f6fe-4ae7-8496-a39ef426a834" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_BusinessCombinationDisclosureAndGoodwillAndIntangibleAssetsDisclosureTextBlock_75fd28c0-75a9-4dc3-a861-ad2b030adf3b" xlink:href="sum-20220702.xsd#sum_BusinessCombinationDisclosureAndGoodwillAndIntangibleAssetsDisclosureTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_dcb5b50c-f6fe-4ae7-8496-a39ef426a834" xlink:to="loc_sum_BusinessCombinationDisclosureAndGoodwillAndIntangibleAssetsDisclosureTextBlock_75fd28c0-75a9-4dc3-a861-ad2b030adf3b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8929ce82-80e1-476a-b5ce-bcc9ea3146c0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_dcb5b50c-f6fe-4ae7-8496-a39ef426a834" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8929ce82-80e1-476a-b5ce-bcc9ea3146c0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_f9fbda96-7eb4-42f3-ba46-bd8bb1ecbe99" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8929ce82-80e1-476a-b5ce-bcc9ea3146c0" xlink:to="loc_dei_LegalEntityAxis_f9fbda96-7eb4-42f3-ba46-bd8bb1ecbe99" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f9fbda96-7eb4-42f3-ba46-bd8bb1ecbe99_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_f9fbda96-7eb4-42f3-ba46-bd8bb1ecbe99" xlink:to="loc_dei_EntityDomain_f9fbda96-7eb4-42f3-ba46-bd8bb1ecbe99_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_9e4f2569-7e04-43da-97a6-18e01a7a71e3" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_f9fbda96-7eb4-42f3-ba46-bd8bb1ecbe99" xlink:to="loc_dei_EntityDomain_9e4f2569-7e04-43da-97a6-18e01a7a71e3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_0b8919d8-c44b-4f0d-9068-9f40b9733c7c" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_9e4f2569-7e04-43da-97a6-18e01a7a71e3" xlink:to="loc_sum_SummitMaterialsLlcMember_0b8919d8-c44b-4f0d-9068-9f40b9733c7c" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESTables" xlink:type="simple" xlink:href="sum-20220702.xsd#ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESTables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESTables" xlink:type="extended" id="icf8de97098bf4c47a238577d08e2adb6_ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESTables">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_c4fb66f2-d37e-4847-8496-c9d5a5d61f4c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfBusinessAcquisitionsNumberOfAcquisitionsByRegionTableTextBlock_702d9502-2c63-4685-aeff-43ef7e0cb65c" xlink:href="sum-20220702.xsd#sum_ScheduleOfBusinessAcquisitionsNumberOfAcquisitionsByRegionTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c4fb66f2-d37e-4847-8496-c9d5a5d61f4c" xlink:to="loc_sum_ScheduleOfBusinessAcquisitionsNumberOfAcquisitionsByRegionTableTextBlock_702d9502-2c63-4685-aeff-43ef7e0cb65c" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRecognizedIdentifiedAssetsAcquiredAndLiabilitiesAssumedTableTextBlock_4689d557-af2f-44bc-949c-9ff4a14f147d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfRecognizedIdentifiedAssetsAcquiredAndLiabilitiesAssumedTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c4fb66f2-d37e-4847-8496-c9d5a5d61f4c" xlink:to="loc_us-gaap_ScheduleOfRecognizedIdentifiedAssetsAcquiredAndLiabilitiesAssumedTableTextBlock_4689d557-af2f-44bc-949c-9ff4a14f147d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTextBlock_d978efb3-57e8-4ee5-9fc4-d9877d3dac65" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfGoodwillTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c4fb66f2-d37e-4847-8496-c9d5a5d61f4c" xlink:to="loc_us-gaap_ScheduleOfGoodwillTextBlock_d978efb3-57e8-4ee5-9fc4-d9877d3dac65" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock_74f58571-cad2-4937-beaa-356dcfb23519" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c4fb66f2-d37e-4847-8496-c9d5a5d61f4c" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock_74f58571-cad2-4937-beaa-356dcfb23519" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleofFiniteLivedIntangibleAssetsFutureAmortizationExpenseTableTextBlock_11529287-43cc-4a78-a25c-3602460932a3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleofFiniteLivedIntangibleAssetsFutureAmortizationExpenseTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c4fb66f2-d37e-4847-8496-c9d5a5d61f4c" xlink:to="loc_us-gaap_ScheduleofFiniteLivedIntangibleAssetsFutureAmortizationExpenseTableTextBlock_11529287-43cc-4a78-a25c-3602460932a3" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_c808e43b-b445-4947-845c-9c0c08a874b5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c4fb66f2-d37e-4847-8496-c9d5a5d61f4c" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_c808e43b-b445-4947-845c-9c0c08a874b5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_b02b4c23-aa3b-4105-adc0-89f27e1c5104" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_c808e43b-b445-4947-845c-9c0c08a874b5" xlink:to="loc_dei_LegalEntityAxis_b02b4c23-aa3b-4105-adc0-89f27e1c5104" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_b02b4c23-aa3b-4105-adc0-89f27e1c5104_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_b02b4c23-aa3b-4105-adc0-89f27e1c5104" xlink:to="loc_dei_EntityDomain_b02b4c23-aa3b-4105-adc0-89f27e1c5104_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_cc89fcc1-2bad-4a3c-a3cd-6d1fb567787d" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_b02b4c23-aa3b-4105-adc0-89f27e1c5104" xlink:to="loc_dei_EntityDomain_cc89fcc1-2bad-4a3c-a3cd-6d1fb567787d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_575e45a8-af13-4e0d-ac28-8d1684f49b17" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_cc89fcc1-2bad-4a3c-a3cd-6d1fb567787d" xlink:to="loc_sum_SummitMaterialsLlcMember_575e45a8-af13-4e0d-ac28-8d1684f49b17" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESAcquisitionsbyRegionDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESAcquisitionsbyRegionDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESAcquisitionsbyRegionDetails" xlink:type="extended" id="i033f008072a74350bff042b4d81d9365_ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESAcquisitionsbyRegionDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_5edde2bf-8f6a-49e8-a41f-e1e39bdec864" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfBusinessesAcquired_73f4d318-86e1-4617-838c-a6a537507c12" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfBusinessesAcquired"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_5edde2bf-8f6a-49e8-a41f-e1e39bdec864" xlink:to="loc_us-gaap_NumberOfBusinessesAcquired_73f4d318-86e1-4617-838c-a6a537507c12" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_044ad1a2-e28a-48d2-9278-0d4c70229399" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_5edde2bf-8f6a-49e8-a41f-e1e39bdec864" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_044ad1a2-e28a-48d2-9278-0d4c70229399" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_b4b58445-eb45-46f4-a215-062e7d7ff407" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_044ad1a2-e28a-48d2-9278-0d4c70229399" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_b4b58445-eb45-46f4-a215-062e7d7ff407" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_b4b58445-eb45-46f4-a215-062e7d7ff407_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b4b58445-eb45-46f4-a215-062e7d7ff407" xlink:to="loc_us-gaap_SegmentDomain_b4b58445-eb45-46f4-a215-062e7d7ff407_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_48d48569-aead-457f-a794-1d82cf68e250" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b4b58445-eb45-46f4-a215-062e7d7ff407" xlink:to="loc_us-gaap_SegmentDomain_48d48569-aead-457f-a794-1d82cf68e250" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_WestMember_aa1ca282-f0cc-4c5f-a7e4-edc088c201be" xlink:href="sum-20220702.xsd#sum_WestMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_48d48569-aead-457f-a794-1d82cf68e250" xlink:to="loc_sum_WestMember_aa1ca282-f0cc-4c5f-a7e4-edc088c201be" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_EastMember_c50180c8-2b37-4e77-9ce3-86ef981227fa" xlink:href="sum-20220702.xsd#sum_EastMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_48d48569-aead-457f-a794-1d82cf68e250" xlink:to="loc_sum_EastMember_c50180c8-2b37-4e77-9ce3-86ef981227fa" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_6aaca7f5-afe1-4608-a3cd-0721f3c16320" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_044ad1a2-e28a-48d2-9278-0d4c70229399" xlink:to="loc_dei_LegalEntityAxis_6aaca7f5-afe1-4608-a3cd-0721f3c16320" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_6aaca7f5-afe1-4608-a3cd-0721f3c16320_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_6aaca7f5-afe1-4608-a3cd-0721f3c16320" xlink:to="loc_dei_EntityDomain_6aaca7f5-afe1-4608-a3cd-0721f3c16320_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_96774759-3384-435b-b38b-2527abfe5986" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_6aaca7f5-afe1-4608-a3cd-0721f3c16320" xlink:to="loc_dei_EntityDomain_96774759-3384-435b-b38b-2527abfe5986" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_5c1efc48-fc65-4850-9138-ff35920be5ee" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_96774759-3384-435b-b38b-2527abfe5986" xlink:to="loc_sum_SummitMaterialsLlcMember_5c1efc48-fc65-4850-9138-ff35920be5ee" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESSummaryofAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESSummaryofAssetsAcquiredandLiabilitiesAssumedDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESSummaryofAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="extended" id="i96f82910d36848699d77c6f6e732fdbe_ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESSummaryofAssetsAcquiredandLiabilitiesAssumedDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancialAssets_43a95036-a3aa-461e-9615-ff7d0c9c5435" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancialAssets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancialAssets_43a95036-a3aa-461e-9615-ff7d0c9c5435" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_37b4d8de-0104-41ea-be07-cd9b5e04e221" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_37b4d8de-0104-41ea-be07-cd9b5e04e221" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_f533da2e-f722-45ee-a7eb-5dad2a14e342" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_f533da2e-f722-45ee-a7eb-5dad2a14e342" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_33feed21-74b4-40b5-ac4b-4dde86aa6edc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_33feed21-74b4-40b5-ac4b-4dde86aa6edc" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssets_993f71f2-e137-41a8-af51-379c1a5b5c6b" xlink:href="sum-20220702.xsd#sum_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_sum_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherAssets_993f71f2-e137-41a8-af51-379c1a5b5c6b" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancialLiabilities_836ac900-49c1-4466-a057-7731a48df173" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancialLiabilities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancialLiabilities_836ac900-49c1-4466-a057-7731a48df173" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_b7785003-74df-425c-92b9-1b767871f6c0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_b7785003-74df-425c-92b9-1b767871f6c0" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_205d8467-2cb1-4d2d-99cc-29bc5257f468" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_205d8467-2cb1-4d2d-99cc-29bc5257f468" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_da010197-1e80-4ff9-84ab-78e7fd115f2d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_Goodwill_da010197-1e80-4ff9-84ab-78e7fd115f2d" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_9db21c3a-fb3b-4dbd-aa6d-e0d558a73a07" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_9db21c3a-fb3b-4dbd-aa6d-e0d558a73a07" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_4df03f3b-cf31-495c-bdae-5c47493ce4ec" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_4df03f3b-cf31-495c-bdae-5c47493ce4ec" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredOther1_4ccdb236-a366-4223-ac6d-573f941e66f4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferredOther1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredOther1_4ccdb236-a366-4223-ac6d-573f941e66f4" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_0fcc5265-9348-4505-8867-20b8f0f4e927" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_0fcc5265-9348-4505-8867-20b8f0f4e927" xlink:type="arc" order="12"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_ac0f6acb-6933-4834-88ee-9fbde92b567a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_3c3d99a9-fcd6-42b2-81f6-80679ffd8ef8" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_ac0f6acb-6933-4834-88ee-9fbde92b567a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_8eb10b0f-90c1-4e49-afbf-df4886f8486a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_ac0f6acb-6933-4834-88ee-9fbde92b567a" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_8eb10b0f-90c1-4e49-afbf-df4886f8486a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8eb10b0f-90c1-4e49-afbf-df4886f8486a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_8eb10b0f-90c1-4e49-afbf-df4886f8486a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8eb10b0f-90c1-4e49-afbf-df4886f8486a_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_ac07e24a-0b3b-457e-a9e3-196538d2c878" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_8eb10b0f-90c1-4e49-afbf-df4886f8486a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_ac07e24a-0b3b-457e-a9e3-196538d2c878" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_9f287ddf-321e-4950-9a65-bca92ed5728b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_ac07e24a-0b3b-457e-a9e3-196538d2c878" xlink:to="loc_us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_9f287ddf-321e-4950-9a65-bca92ed5728b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_1164481e-2e49-491d-acfa-d6765878526d" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_ac0f6acb-6933-4834-88ee-9fbde92b567a" xlink:to="loc_dei_LegalEntityAxis_1164481e-2e49-491d-acfa-d6765878526d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_1164481e-2e49-491d-acfa-d6765878526d_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1164481e-2e49-491d-acfa-d6765878526d" xlink:to="loc_dei_EntityDomain_1164481e-2e49-491d-acfa-d6765878526d_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a98007b4-6dbf-47fd-a8f3-9b6442630909" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1164481e-2e49-491d-acfa-d6765878526d" xlink:to="loc_dei_EntityDomain_a98007b4-6dbf-47fd-a8f3-9b6442630909" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_a329c7e9-9fe4-419b-b3c3-149240ed9c97" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a98007b4-6dbf-47fd-a8f3-9b6442630909" xlink:to="loc_sum_SummitMaterialsLlcMember_a329c7e9-9fe4-419b-b3c3-149240ed9c97" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESSummaryofGoodwillbyReportableSegmentsDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESSummaryofGoodwillbyReportableSegmentsDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESSummaryofGoodwillbyReportableSegmentsDetails" xlink:type="extended" id="i8e2e334c1e60421aa0d3219d6b929f03_ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESSummaryofGoodwillbyReportableSegmentsDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_c1a65b19-f399-4dba-a208-66cfef9a272e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GoodwillLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_82d4dbca-8735-4e94-91eb-8cbb5c9a148c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GoodwillRollForward"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_c1a65b19-f399-4dba-a208-66cfef9a272e" xlink:to="loc_us-gaap_GoodwillRollForward_82d4dbca-8735-4e94-91eb-8cbb5c9a148c" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_bf93663b-3247-4678-ae18-6b941fdcb60b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_82d4dbca-8735-4e94-91eb-8cbb5c9a148c" xlink:to="loc_us-gaap_Goodwill_bf93663b-3247-4678-ae18-6b941fdcb60b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_GoodwillDisposedDuringPeriod_ffa7dcf0-0387-46b4-9ec4-fde7c922f78c" xlink:href="sum-20220702.xsd#sum_GoodwillDisposedDuringPeriod"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_82d4dbca-8735-4e94-91eb-8cbb5c9a148c" xlink:to="loc_sum_GoodwillDisposedDuringPeriod_ffa7dcf0-0387-46b4-9ec4-fde7c922f78c" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_cc50c5c1-7232-42c5-954c-5b1e8342cb36" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GoodwillForeignCurrencyTranslationGainLoss"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_82d4dbca-8735-4e94-91eb-8cbb5c9a148c" xlink:to="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_cc50c5c1-7232-42c5-954c-5b1e8342cb36" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_abbedc93-0ab0-493e-a0ee-90d2928aafbe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_b8105cdf-4092-4665-9876-c5255e3339ed" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfGoodwillTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_c1a65b19-f399-4dba-a208-66cfef9a272e" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_b8105cdf-4092-4665-9876-c5255e3339ed" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_2196ae2a-49fb-42e0-996b-17a49706f55e" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_b8105cdf-4092-4665-9876-c5255e3339ed" xlink:to="loc_dei_LegalEntityAxis_2196ae2a-49fb-42e0-996b-17a49706f55e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_2196ae2a-49fb-42e0-996b-17a49706f55e_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_2196ae2a-49fb-42e0-996b-17a49706f55e" xlink:to="loc_dei_EntityDomain_2196ae2a-49fb-42e0-996b-17a49706f55e_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_afc48532-ef39-41a3-8c75-15e6482cb1c2" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_2196ae2a-49fb-42e0-996b-17a49706f55e" xlink:to="loc_dei_EntityDomain_afc48532-ef39-41a3-8c75-15e6482cb1c2" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_270bee34-5ec2-4ca0-a9bd-b763cdafc587" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_afc48532-ef39-41a3-8c75-15e6482cb1c2" xlink:to="loc_sum_SummitMaterialsLlcMember_270bee34-5ec2-4ca0-a9bd-b763cdafc587" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_7eca5e6b-e68c-4b7c-822c-bb9887d436fa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_b8105cdf-4092-4665-9876-c5255e3339ed" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_7eca5e6b-e68c-4b7c-822c-bb9887d436fa" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_7eca5e6b-e68c-4b7c-822c-bb9887d436fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_7eca5e6b-e68c-4b7c-822c-bb9887d436fa" xlink:to="loc_us-gaap_SegmentDomain_7eca5e6b-e68c-4b7c-822c-bb9887d436fa_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_ec6ae7c7-e07e-4a6d-8d86-1384f75f7f74" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_7eca5e6b-e68c-4b7c-822c-bb9887d436fa" xlink:to="loc_us-gaap_SegmentDomain_ec6ae7c7-e07e-4a6d-8d86-1384f75f7f74" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_WestMember_af80a48b-ad24-4d9e-a8b4-804263c5c791" xlink:href="sum-20220702.xsd#sum_WestMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_ec6ae7c7-e07e-4a6d-8d86-1384f75f7f74" xlink:to="loc_sum_WestMember_af80a48b-ad24-4d9e-a8b4-804263c5c791" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_EastMember_f838d517-4c98-43ab-8302-178927f96402" xlink:href="sum-20220702.xsd#sum_EastMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_ec6ae7c7-e07e-4a6d-8d86-1384f75f7f74" xlink:to="loc_sum_EastMember_f838d517-4c98-43ab-8302-178927f96402" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CementMember_70d59d3a-3138-4ca7-b0cc-1630fbb98a49" xlink:href="sum-20220702.xsd#sum_CementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_ec6ae7c7-e07e-4a6d-8d86-1384f75f7f74" xlink:to="loc_sum_CementMember_70d59d3a-3138-4ca7-b0cc-1630fbb98a49" xlink:type="arc" order="2"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESIntangibleAssetsByTypeDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESIntangibleAssetsByTypeDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESIntangibleAssetsByTypeDetails" xlink:type="extended" id="idb08fd488e4d4d7facc628b97808dda8_ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESIntangibleAssetsByTypeDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_d7a16d0d-1dce-4b23-8168-bf8d40517a94" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_fc582a87-916d-4432-a882-8a5afd75ffed" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_d7a16d0d-1dce-4b23-8168-bf8d40517a94" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_fc582a87-916d-4432-a882-8a5afd75ffed" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_c1153c3c-ddb9-416f-8910-9625677df056" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_d7a16d0d-1dce-4b23-8168-bf8d40517a94" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_c1153c3c-ddb9-416f-8910-9625677df056" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_8b9b4bd9-160e-4440-b16a-5d3dd82f413f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_d7a16d0d-1dce-4b23-8168-bf8d40517a94" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_8b9b4bd9-160e-4440-b16a-5d3dd82f413f" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_dfef879d-a083-42b5-9912-3bfceca0186e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_d7a16d0d-1dce-4b23-8168-bf8d40517a94" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_dfef879d-a083-42b5-9912-3bfceca0186e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_9760b0d5-44cf-41e4-a192-4f60945973e4" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_dfef879d-a083-42b5-9912-3bfceca0186e" xlink:to="loc_dei_LegalEntityAxis_9760b0d5-44cf-41e4-a192-4f60945973e4" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_9760b0d5-44cf-41e4-a192-4f60945973e4_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_9760b0d5-44cf-41e4-a192-4f60945973e4" xlink:to="loc_dei_EntityDomain_9760b0d5-44cf-41e4-a192-4f60945973e4_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e60dd489-4ccd-41f2-b7dc-11ae73eec195" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_9760b0d5-44cf-41e4-a192-4f60945973e4" xlink:to="loc_dei_EntityDomain_e60dd489-4ccd-41f2-b7dc-11ae73eec195" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_1ab077a7-ec68-4ffe-895b-84c9993453b6" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_e60dd489-4ccd-41f2-b7dc-11ae73eec195" xlink:to="loc_sum_SummitMaterialsLlcMember_1ab077a7-ec68-4ffe-895b-84c9993453b6" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_dbc19d53-d160-46bf-8468-5f850e8e4664" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_dfef879d-a083-42b5-9912-3bfceca0186e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_dbc19d53-d160-46bf-8468-5f850e8e4664" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_dbc19d53-d160-46bf-8468-5f850e8e4664_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_dbc19d53-d160-46bf-8468-5f850e8e4664" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_dbc19d53-d160-46bf-8468-5f850e8e4664_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_38de40ca-914b-4d99-85b8-830bcdc11f1f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_dbc19d53-d160-46bf-8468-5f850e8e4664" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_38de40ca-914b-4d99-85b8-830bcdc11f1f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_IntangibleAssetsExcludingIntangibleAssetsHeldForSaleMember_0e2c96c6-da24-4f76-94ff-5b129542ca94" xlink:href="sum-20220702.xsd#sum_IntangibleAssetsExcludingIntangibleAssetsHeldForSaleMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_38de40ca-914b-4d99-85b8-830bcdc11f1f" xlink:to="loc_sum_IntangibleAssetsExcludingIntangibleAssetsHeldForSaleMember_0e2c96c6-da24-4f76-94ff-5b129542ca94" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionPermitsMember_47c43911-b003-40e7-93ec-3e596913232f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConstructionPermitsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IntangibleAssetsExcludingIntangibleAssetsHeldForSaleMember_0e2c96c6-da24-4f76-94ff-5b129542ca94" xlink:to="loc_us-gaap_ConstructionPermitsMember_47c43911-b003-40e7-93ec-3e596913232f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseAgreementsMember_a287eaca-b92e-41cf-b5b1-12f6a084ee46" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseAgreementsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IntangibleAssetsExcludingIntangibleAssetsHeldForSaleMember_0e2c96c6-da24-4f76-94ff-5b129542ca94" xlink:to="loc_us-gaap_LeaseAgreementsMember_a287eaca-b92e-41cf-b5b1-12f6a084ee46" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ReserveRightsMember_c5f88108-3385-42ba-a78f-4b6f61c2ff42" xlink:href="sum-20220702.xsd#sum_ReserveRightsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IntangibleAssetsExcludingIntangibleAssetsHeldForSaleMember_0e2c96c6-da24-4f76-94ff-5b129542ca94" xlink:to="loc_sum_ReserveRightsMember_c5f88108-3385-42ba-a78f-4b6f61c2ff42" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_40bab936-1e04-425a-a7cd-0097f38c96ed" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherIntangibleAssetsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IntangibleAssetsExcludingIntangibleAssetsHeldForSaleMember_0e2c96c6-da24-4f76-94ff-5b129542ca94" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_40bab936-1e04-425a-a7cd-0097f38c96ed" xlink:type="arc" order="4"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESAmortizationExpenseDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESAmortizationExpenseDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESAmortizationExpenseDetails" xlink:type="extended" id="i01ea16af2aec42f9ab818d2657f1f2fc_ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESAmortizationExpenseDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_81534b54-08d8-4871-81db-0b157b3aacbf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_17b27134-d108-4ac6-b7ee-687e79e08b40" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_81534b54-08d8-4871-81db-0b157b3aacbf" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_17b27134-d108-4ac6-b7ee-687e79e08b40" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_1fcf5a81-7f51-406c-aa82-4b5e998766e0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_81534b54-08d8-4871-81db-0b157b3aacbf" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_1fcf5a81-7f51-406c-aa82-4b5e998766e0" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_fb2198fa-9032-403f-8425-c384dd64b2a3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_1fcf5a81-7f51-406c-aa82-4b5e998766e0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_fb2198fa-9032-403f-8425-c384dd64b2a3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_bbe83a40-7337-43e4-8645-835730def4f6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_1fcf5a81-7f51-406c-aa82-4b5e998766e0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_bbe83a40-7337-43e4-8645-835730def4f6" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_1422e15f-f22a-4e3e-88a6-eef784c362a5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_1fcf5a81-7f51-406c-aa82-4b5e998766e0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_1422e15f-f22a-4e3e-88a6-eef784c362a5" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_700fa54b-063c-428e-8654-368bd22b3d12" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_1fcf5a81-7f51-406c-aa82-4b5e998766e0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_700fa54b-063c-428e-8654-368bd22b3d12" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_80573b3e-c73f-41f5-85b4-2b093a79a116" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_1fcf5a81-7f51-406c-aa82-4b5e998766e0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_80573b3e-c73f-41f5-85b4-2b093a79a116" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_7f98992c-5fb0-4fb5-b31b-f590f6572a13" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_1fcf5a81-7f51-406c-aa82-4b5e998766e0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_7f98992c-5fb0-4fb5-b31b-f590f6572a13" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_d2c50101-19cc-4e9f-b375-04751845d1af" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_1fcf5a81-7f51-406c-aa82-4b5e998766e0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_d2c50101-19cc-4e9f-b375-04751845d1af" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_4ac16d4d-fe62-4a78-836e-16d0954a346b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract_1fcf5a81-7f51-406c-aa82-4b5e998766e0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_4ac16d4d-fe62-4a78-836e-16d0954a346b" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_33ea68e4-abc6-43ea-9e54-233068eca46b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_81534b54-08d8-4871-81db-0b157b3aacbf" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_33ea68e4-abc6-43ea-9e54-233068eca46b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_0fb2564c-2734-4125-aebf-f490b201ca91" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_33ea68e4-abc6-43ea-9e54-233068eca46b" xlink:to="loc_dei_LegalEntityAxis_0fb2564c-2734-4125-aebf-f490b201ca91" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0fb2564c-2734-4125-aebf-f490b201ca91_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_0fb2564c-2734-4125-aebf-f490b201ca91" xlink:to="loc_dei_EntityDomain_0fb2564c-2734-4125-aebf-f490b201ca91_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f70a1244-4ada-4ea6-9d3f-e94c071a5132" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_0fb2564c-2734-4125-aebf-f490b201ca91" xlink:to="loc_dei_EntityDomain_f70a1244-4ada-4ea6-9d3f-e94c071a5132" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_d5560f99-7b8c-4492-92ec-dffcbcd6f400" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_f70a1244-4ada-4ea6-9d3f-e94c071a5132" xlink:to="loc_sum_SummitMaterialsLlcMember_d5560f99-7b8c-4492-92ec-dffcbcd6f400" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESNarrativeDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESNarrativeDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESNarrativeDetails" xlink:type="extended" id="i83b94a92bd4145fdb6f59c560cc4db97_ACQUISITIONSDISPOSTIONSGOODWILLANDINTANGIBLESNarrativeDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_c80c73ed-a16d-433a-86b3-740e5436574d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessAcquisitionLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_NumberOfBusinessesSold_e9721f8c-d064-45de-849d-311f019bfafd" xlink:href="sum-20220702.xsd#sum_NumberOfBusinessesSold"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c80c73ed-a16d-433a-86b3-740e5436574d" xlink:to="loc_sum_NumberOfBusinessesSold_e9721f8c-d064-45de-849d-311f019bfafd" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_7c2febab-bf4a-4cdd-96b9-b9a1d5d6478c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c80c73ed-a16d-433a-86b3-740e5436574d" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_7c2febab-bf4a-4cdd-96b9-b9a1d5d6478c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_ffb8ccca-7093-4ab1-a8b6-8e718967b9dc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c80c73ed-a16d-433a-86b3-740e5436574d" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_ffb8ccca-7093-4ab1-a8b6-8e718967b9dc" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_99baf43e-f156-40d8-b99a-a0f51a9a11d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c80c73ed-a16d-433a-86b3-740e5436574d" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_99baf43e-f156-40d8-b99a-a0f51a9a11d2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a7130bdd-aec0-4055-b76e-a59d68280672" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_99baf43e-f156-40d8-b99a-a0f51a9a11d2" xlink:to="loc_dei_LegalEntityAxis_a7130bdd-aec0-4055-b76e-a59d68280672" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a7130bdd-aec0-4055-b76e-a59d68280672_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a7130bdd-aec0-4055-b76e-a59d68280672" xlink:to="loc_dei_EntityDomain_a7130bdd-aec0-4055-b76e-a59d68280672_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0dea29a3-7b3d-4f0e-96a6-5d58a8809286" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a7130bdd-aec0-4055-b76e-a59d68280672" xlink:to="loc_dei_EntityDomain_0dea29a3-7b3d-4f0e-96a6-5d58a8809286" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_aa3690c6-f8c5-4aac-ad3b-9cdd5893e1df" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0dea29a3-7b3d-4f0e-96a6-5d58a8809286" xlink:to="loc_sum_SummitMaterialsLlcMember_aa3690c6-f8c5-4aac-ad3b-9cdd5893e1df" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_9d7cc895-df1c-4082-ad8b-288b445288c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_99baf43e-f156-40d8-b99a-a0f51a9a11d2" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_9d7cc895-df1c-4082-ad8b-288b445288c9" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_9d7cc895-df1c-4082-ad8b-288b445288c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_9d7cc895-df1c-4082-ad8b-288b445288c9" xlink:to="loc_us-gaap_SegmentDomain_9d7cc895-df1c-4082-ad8b-288b445288c9_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_e108a8a4-17df-433e-b01f-c3114cf12277" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_9d7cc895-df1c-4082-ad8b-288b445288c9" xlink:to="loc_us-gaap_SegmentDomain_e108a8a4-17df-433e-b01f-c3114cf12277" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_EastMember_792f0b51-6d00-4cdc-a300-2c50919cf3bd" xlink:href="sum-20220702.xsd#sum_EastMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_e108a8a4-17df-433e-b01f-c3114cf12277" xlink:to="loc_sum_EastMember_792f0b51-6d00-4cdc-a300-2c50919cf3bd" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/REVENUERECOGNITION" xlink:type="simple" xlink:href="sum-20220702.xsd#REVENUERECOGNITION"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/REVENUERECOGNITION" xlink:type="extended" id="ide4c675e31c6442ca656c09237667a1b_REVENUERECOGNITION">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_c64d38c4-a907-425e-93f5-ca7539ca7c1c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock_561ffb72-1bfe-41fe-b81c-c3f10ca017ca" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_c64d38c4-a907-425e-93f5-ca7539ca7c1c" xlink:to="loc_us-gaap_LoansNotesTradeAndOtherReceivablesDisclosureTextBlock_561ffb72-1bfe-41fe-b81c-c3f10ca017ca" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_a12976cd-82d1-4b34-89bf-6b9472e0e02f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_c64d38c4-a907-425e-93f5-ca7539ca7c1c" xlink:to="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_a12976cd-82d1-4b34-89bf-6b9472e0e02f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_00907698-4861-4096-9b45-ec1a4934a4f1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_a12976cd-82d1-4b34-89bf-6b9472e0e02f" xlink:to="loc_dei_LegalEntityAxis_00907698-4861-4096-9b45-ec1a4934a4f1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_00907698-4861-4096-9b45-ec1a4934a4f1_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_00907698-4861-4096-9b45-ec1a4934a4f1" xlink:to="loc_dei_EntityDomain_00907698-4861-4096-9b45-ec1a4934a4f1_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_2302d978-c34c-415b-80a9-d8b476d464c8" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_00907698-4861-4096-9b45-ec1a4934a4f1" xlink:to="loc_dei_EntityDomain_2302d978-c34c-415b-80a9-d8b476d464c8" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_151be962-2c8f-4a9f-af6f-cef7e761d5af" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2302d978-c34c-415b-80a9-d8b476d464c8" xlink:to="loc_sum_SummitMaterialsLlcMember_151be962-2c8f-4a9f-af6f-cef7e761d5af" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/REVENUERECOGNITIONTables" xlink:type="simple" xlink:href="sum-20220702.xsd#REVENUERECOGNITIONTables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/REVENUERECOGNITIONTables" xlink:type="extended" id="i63f2ade96a0041d28ec20344190f51de_REVENUERECOGNITIONTables">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_d603d27b-9579-4bcd-a353-0bf63c0d5e90" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_b82ae1bc-9033-4b64-9b82-7a2b8cae841d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_d603d27b-9579-4bcd-a353-0bf63c0d5e90" xlink:to="loc_us-gaap_DisaggregationOfRevenueTableTextBlock_b82ae1bc-9033-4b64-9b82-7a2b8cae841d" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_69947bae-071f-4ad3-8190-e2581d8c394c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_d603d27b-9579-4bcd-a353-0bf63c0d5e90" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_69947bae-071f-4ad3-8190-e2581d8c394c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_ad5184d3-1dbb-4528-a20e-5d29148ddccf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_d603d27b-9579-4bcd-a353-0bf63c0d5e90" xlink:to="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_ad5184d3-1dbb-4528-a20e-5d29148ddccf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_97a45183-76a4-4623-9b70-016f25d76323" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_ad5184d3-1dbb-4528-a20e-5d29148ddccf" xlink:to="loc_dei_LegalEntityAxis_97a45183-76a4-4623-9b70-016f25d76323" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_97a45183-76a4-4623-9b70-016f25d76323_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_97a45183-76a4-4623-9b70-016f25d76323" xlink:to="loc_dei_EntityDomain_97a45183-76a4-4623-9b70-016f25d76323_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_310b8d1a-e1a9-48a3-adf7-3176f13f67c4" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_97a45183-76a4-4623-9b70-016f25d76323" xlink:to="loc_dei_EntityDomain_310b8d1a-e1a9-48a3-adf7-3176f13f67c4" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_f02ce847-4407-4cd9-9380-e95b74a031dc" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_310b8d1a-e1a9-48a3-adf7-3176f13f67c4" xlink:to="loc_sum_SummitMaterialsLlcMember_f02ce847-4407-4cd9-9380-e95b74a031dc" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/REVENUERECOGNITIONByProductDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#REVENUERECOGNITIONByProductDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/REVENUERECOGNITIONByProductDetails" xlink:type="extended" id="i2f763c8716564aa8933174bc41553598_REVENUERECOGNITIONByProductDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_42ee3d1a-60f9-4406-90cc-f02d04ba714a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_4d5ad713-a810-4768-8a31-848df19f8aaf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_42ee3d1a-60f9-4406-90cc-f02d04ba714a" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_4d5ad713-a810-4768-8a31-848df19f8aaf" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_7e410a0d-beed-4b88-bf72-851da040b0f0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_42ee3d1a-60f9-4406-90cc-f02d04ba714a" xlink:to="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_7e410a0d-beed-4b88-bf72-851da040b0f0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_278fec0d-df2c-4137-bf06-1ddd09acd141" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_7e410a0d-beed-4b88-bf72-851da040b0f0" xlink:to="loc_dei_LegalEntityAxis_278fec0d-df2c-4137-bf06-1ddd09acd141" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_278fec0d-df2c-4137-bf06-1ddd09acd141_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_278fec0d-df2c-4137-bf06-1ddd09acd141" xlink:to="loc_dei_EntityDomain_278fec0d-df2c-4137-bf06-1ddd09acd141_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_4404d4db-5718-4b99-ab66-44a8fafacc18" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_278fec0d-df2c-4137-bf06-1ddd09acd141" xlink:to="loc_dei_EntityDomain_4404d4db-5718-4b99-ab66-44a8fafacc18" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_e3457e03-f25d-4d37-83c4-e49e5213a705" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_4404d4db-5718-4b99-ab66-44a8fafacc18" xlink:to="loc_sum_SummitMaterialsLlcMember_e3457e03-f25d-4d37-83c4-e49e5213a705" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_9af06ecd-ad28-4c30-a20c-426e3a5ca5ea" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_7e410a0d-beed-4b88-bf72-851da040b0f0" xlink:to="loc_srt_ProductOrServiceAxis_9af06ecd-ad28-4c30-a20c-426e3a5ca5ea" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_9af06ecd-ad28-4c30-a20c-426e3a5ca5ea_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_9af06ecd-ad28-4c30-a20c-426e3a5ca5ea" xlink:to="loc_srt_ProductsAndServicesDomain_9af06ecd-ad28-4c30-a20c-426e3a5ca5ea_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_dd388909-1c06-4569-86cf-1169c3edfa18" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_9af06ecd-ad28-4c30-a20c-426e3a5ca5ea" xlink:to="loc_srt_ProductsAndServicesDomain_dd388909-1c06-4569-86cf-1169c3edfa18" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AggregatesMember_efb30624-943b-49f5-9487-b1f7b11d74d7" xlink:href="sum-20220702.xsd#sum_AggregatesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_dd388909-1c06-4569-86cf-1169c3edfa18" xlink:to="loc_sum_AggregatesMember_efb30624-943b-49f5-9487-b1f7b11d74d7" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CementMember_94a06514-1ad6-4f30-ab52-5742326bd6de" xlink:href="sum-20220702.xsd#sum_CementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_dd388909-1c06-4569-86cf-1169c3edfa18" xlink:to="loc_sum_CementMember_94a06514-1ad6-4f30-ab52-5742326bd6de" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ReadyMixedConcreteMember_d9f1ffef-4c69-436e-816e-4b33887eba71" xlink:href="sum-20220702.xsd#sum_ReadyMixedConcreteMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_dd388909-1c06-4569-86cf-1169c3edfa18" xlink:to="loc_sum_ReadyMixedConcreteMember_d9f1ffef-4c69-436e-816e-4b33887eba71" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AsphaltMember_b8926d19-0c87-4af4-8682-455e3809fee1" xlink:href="sum-20220702.xsd#sum_AsphaltMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_dd388909-1c06-4569-86cf-1169c3edfa18" xlink:to="loc_sum_AsphaltMember_b8926d19-0c87-4af4-8682-455e3809fee1" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_PavingAndRelatedServicesMember_13513c34-5354-456a-9645-45fdb41856cf" xlink:href="sum-20220702.xsd#sum_PavingAndRelatedServicesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_dd388909-1c06-4569-86cf-1169c3edfa18" xlink:to="loc_sum_PavingAndRelatedServicesMember_13513c34-5354-456a-9645-45fdb41856cf" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_OtherProductsOrServicesMember_d0040ce9-755a-4867-a0f5-31fc5b2890a7" xlink:href="sum-20220702.xsd#sum_OtherProductsOrServicesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_dd388909-1c06-4569-86cf-1169c3edfa18" xlink:to="loc_sum_OtherProductsOrServicesMember_d0040ce9-755a-4867-a0f5-31fc5b2890a7" xlink:type="arc" order="5"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/REVENUERECOGNITIONSummaryofAccountsReceivableNetDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#REVENUERECOGNITIONSummaryofAccountsReceivableNetDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/REVENUERECOGNITIONSummaryofAccountsReceivableNetDetails" xlink:type="extended" id="i317deb1495c64ed0a8b4a5a47b818ca4_REVENUERECOGNITIONSummaryofAccountsReceivableNetDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_3bed5259-0c7a-457a-8ea3-02bacf37cc5d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_TradeAccountsReceivable_863e714b-c330-4980-800c-841222209305" xlink:href="sum-20220702.xsd#sum_TradeAccountsReceivable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_3bed5259-0c7a-457a-8ea3-02bacf37cc5d" xlink:to="loc_sum_TradeAccountsReceivable_863e714b-c330-4980-800c-841222209305" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BilledContractReceivables_7505116d-71cb-4d02-be5a-119ce6aa91e8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BilledContractReceivables"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_3bed5259-0c7a-457a-8ea3-02bacf37cc5d" xlink:to="loc_us-gaap_BilledContractReceivables_7505116d-71cb-4d02-be5a-119ce6aa91e8" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_RetentionReceivables_abbc81c3-9482-4025-8a70-922a74a4aec4" xlink:href="sum-20220702.xsd#sum_RetentionReceivables"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_3bed5259-0c7a-457a-8ea3-02bacf37cc5d" xlink:to="loc_sum_RetentionReceivables_abbc81c3-9482-4025-8a70-922a74a4aec4" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableRelatedParties_4cef681d-f71e-41aa-9365-4acbdc8d11c2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableRelatedParties"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_3bed5259-0c7a-457a-8ea3-02bacf37cc5d" xlink:to="loc_us-gaap_AccountsReceivableRelatedParties_4cef681d-f71e-41aa-9365-4acbdc8d11c2" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableGrossCurrent_12327658-f335-41bb-a61d-8ed9a1db559c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableGrossCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_3bed5259-0c7a-457a-8ea3-02bacf37cc5d" xlink:to="loc_us-gaap_AccountsReceivableGrossCurrent_12327658-f335-41bb-a61d-8ed9a1db559c" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_83736464-56ed-49fc-b1ce-55d1ca1c8bda" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_3bed5259-0c7a-457a-8ea3-02bacf37cc5d" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_83736464-56ed-49fc-b1ce-55d1ca1c8bda" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_d81e33e0-3f75-4271-8f32-1aaa3228f2f2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableNetCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_3bed5259-0c7a-457a-8ea3-02bacf37cc5d" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_d81e33e0-3f75-4271-8f32-1aaa3228f2f2" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CollectionAndBillingPeriodRetentionReceivables_9d593726-3a1d-4987-99cc-de1f1f7de86f" xlink:href="sum-20220702.xsd#sum_CollectionAndBillingPeriodRetentionReceivables"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_3bed5259-0c7a-457a-8ea3-02bacf37cc5d" xlink:to="loc_sum_CollectionAndBillingPeriodRetentionReceivables_9d593726-3a1d-4987-99cc-de1f1f7de86f" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_3d04f6c9-9b0e-49e2-9336-ec50379a9c8a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_3bed5259-0c7a-457a-8ea3-02bacf37cc5d" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_3d04f6c9-9b0e-49e2-9336-ec50379a9c8a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_da2cc281-3c1b-468d-8f2f-659fbd4f4657" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_3d04f6c9-9b0e-49e2-9336-ec50379a9c8a" xlink:to="loc_dei_LegalEntityAxis_da2cc281-3c1b-468d-8f2f-659fbd4f4657" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_da2cc281-3c1b-468d-8f2f-659fbd4f4657_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_da2cc281-3c1b-468d-8f2f-659fbd4f4657" xlink:to="loc_dei_EntityDomain_da2cc281-3c1b-468d-8f2f-659fbd4f4657_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_84428b40-7a74-4d13-90fe-fc458fb83153" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_da2cc281-3c1b-468d-8f2f-659fbd4f4657" xlink:to="loc_dei_EntityDomain_84428b40-7a74-4d13-90fe-fc458fb83153" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_290454cf-f396-4192-94b9-8a4522276cb6" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_84428b40-7a74-4d13-90fe-fc458fb83153" xlink:to="loc_sum_SummitMaterialsLlcMember_290454cf-f396-4192-94b9-8a4522276cb6" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_29450140-9e37-46f7-a28c-d7ba7b8f1c4d" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_3d04f6c9-9b0e-49e2-9336-ec50379a9c8a" xlink:to="loc_srt_RangeAxis_29450140-9e37-46f7-a28c-d7ba7b8f1c4d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_29450140-9e37-46f7-a28c-d7ba7b8f1c4d_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_29450140-9e37-46f7-a28c-d7ba7b8f1c4d" xlink:to="loc_srt_RangeMember_29450140-9e37-46f7-a28c-d7ba7b8f1c4d_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_a94af0ed-c24b-4661-a157-dfee95da2024" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_29450140-9e37-46f7-a28c-d7ba7b8f1c4d" xlink:to="loc_srt_RangeMember_a94af0ed-c24b-4661-a157-dfee95da2024" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_df07f349-4a10-4dcd-b1ad-14bcade026cf" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_a94af0ed-c24b-4661-a157-dfee95da2024" xlink:to="loc_srt_MaximumMember_df07f349-4a10-4dcd-b1ad-14bcade026cf" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/INVENTORIES" xlink:type="simple" xlink:href="sum-20220702.xsd#INVENTORIES"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/INVENTORIES" xlink:type="extended" id="ibc8b3c2508254bfd905d262bfbf6406e_INVENTORIES">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryLineItems_666323e4-1ba9-4816-a88f-67aecf1b9756" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryDisclosureTextBlock_05f507b5-16cc-49db-9269-53e7f015a2a5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryDisclosureTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_666323e4-1ba9-4816-a88f-67aecf1b9756" xlink:to="loc_us-gaap_InventoryDisclosureTextBlock_05f507b5-16cc-49db-9269-53e7f015a2a5" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryCurrentTable_ec159483-ace7-49a7-bfbb-59cb3fc45c82" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryCurrentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InventoryLineItems_666323e4-1ba9-4816-a88f-67aecf1b9756" xlink:to="loc_us-gaap_InventoryCurrentTable_ec159483-ace7-49a7-bfbb-59cb3fc45c82" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_af68fd66-658a-4487-9f8d-3ccd571fc72d" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InventoryCurrentTable_ec159483-ace7-49a7-bfbb-59cb3fc45c82" xlink:to="loc_dei_LegalEntityAxis_af68fd66-658a-4487-9f8d-3ccd571fc72d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_af68fd66-658a-4487-9f8d-3ccd571fc72d_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_af68fd66-658a-4487-9f8d-3ccd571fc72d" xlink:to="loc_dei_EntityDomain_af68fd66-658a-4487-9f8d-3ccd571fc72d_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_9f552b5e-b03b-4595-b81a-325fb82c0d84" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_af68fd66-658a-4487-9f8d-3ccd571fc72d" xlink:to="loc_dei_EntityDomain_9f552b5e-b03b-4595-b81a-325fb82c0d84" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_52c8f9b9-f5a9-4006-aac9-1233ef7317cc" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_9f552b5e-b03b-4595-b81a-325fb82c0d84" xlink:to="loc_sum_SummitMaterialsLlcMember_52c8f9b9-f5a9-4006-aac9-1233ef7317cc" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/INVENTORIESTables" xlink:type="simple" xlink:href="sum-20220702.xsd#INVENTORIESTables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/INVENTORIESTables" xlink:type="extended" id="ide604852afce4c6fa0c6e1ad90c45d95_INVENTORIESTables">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryLineItems_f451becb-aad5-4f38-83dd-e1de66762446" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInventoryCurrentTableTextBlock_6c9c66fe-862f-491b-88cf-443b82ef40cb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfInventoryCurrentTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_f451becb-aad5-4f38-83dd-e1de66762446" xlink:to="loc_us-gaap_ScheduleOfInventoryCurrentTableTextBlock_6c9c66fe-862f-491b-88cf-443b82ef40cb" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryCurrentTable_090a7f4b-31b8-4473-adfe-952c1681f7b3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryCurrentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InventoryLineItems_f451becb-aad5-4f38-83dd-e1de66762446" xlink:to="loc_us-gaap_InventoryCurrentTable_090a7f4b-31b8-4473-adfe-952c1681f7b3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_30dfc50a-9472-45d3-9560-94bfbb65ffb6" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InventoryCurrentTable_090a7f4b-31b8-4473-adfe-952c1681f7b3" xlink:to="loc_dei_LegalEntityAxis_30dfc50a-9472-45d3-9560-94bfbb65ffb6" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_30dfc50a-9472-45d3-9560-94bfbb65ffb6_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_30dfc50a-9472-45d3-9560-94bfbb65ffb6" xlink:to="loc_dei_EntityDomain_30dfc50a-9472-45d3-9560-94bfbb65ffb6_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_7c5c6b0c-ca4c-47c7-badb-e20984425780" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_30dfc50a-9472-45d3-9560-94bfbb65ffb6" xlink:to="loc_dei_EntityDomain_7c5c6b0c-ca4c-47c7-badb-e20984425780" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_3bca9a54-90d9-4110-9998-0f7fa35b920d" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7c5c6b0c-ca4c-47c7-badb-e20984425780" xlink:to="loc_sum_SummitMaterialsLlcMember_3bca9a54-90d9-4110-9998-0f7fa35b920d" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/INVENTORIESComponentsofInventoriesDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#INVENTORIESComponentsofInventoriesDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/INVENTORIESComponentsofInventoriesDetails" xlink:type="extended" id="ia6bc38d6f751499e9fcc2ede2c25f3a8_INVENTORIESComponentsofInventoriesDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryLineItems_d19cccd9-2396-46a8-9aa4-71e5c6fd0bd2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryOreStockpilesOnLeachPads_07b41638-9123-414c-91cb-fa9a8274ef73" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryOreStockpilesOnLeachPads"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_d19cccd9-2396-46a8-9aa4-71e5c6fd0bd2" xlink:to="loc_us-gaap_InventoryOreStockpilesOnLeachPads_07b41638-9123-414c-91cb-fa9a8274ef73" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryFinishedGoodsNetOfReserves_4e303c54-a0d7-42ef-8532-8ffa6f1b1126" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryFinishedGoodsNetOfReserves"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_d19cccd9-2396-46a8-9aa4-71e5c6fd0bd2" xlink:to="loc_us-gaap_InventoryFinishedGoodsNetOfReserves_4e303c54-a0d7-42ef-8532-8ffa6f1b1126" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryWorkInProcessNetOfReserves_a628f3f7-8f76-451d-a822-f4ebe877b864" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryWorkInProcessNetOfReserves"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_d19cccd9-2396-46a8-9aa4-71e5c6fd0bd2" xlink:to="loc_us-gaap_InventoryWorkInProcessNetOfReserves_a628f3f7-8f76-451d-a822-f4ebe877b864" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryRawMaterialsNetOfReserves_83fe292e-3e37-470d-b8d7-d0c6bd8ad857" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryRawMaterialsNetOfReserves"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_d19cccd9-2396-46a8-9aa4-71e5c6fd0bd2" xlink:to="loc_us-gaap_InventoryRawMaterialsNetOfReserves_83fe292e-3e37-470d-b8d7-d0c6bd8ad857" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_c9155cb4-43c3-4a2d-a514-d6bbcf500e11" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_d19cccd9-2396-46a8-9aa4-71e5c6fd0bd2" xlink:to="loc_us-gaap_InventoryNet_c9155cb4-43c3-4a2d-a514-d6bbcf500e11" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryCurrentTable_bfceab2f-3180-43c6-82d5-9923cb89a9f6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryCurrentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InventoryLineItems_d19cccd9-2396-46a8-9aa4-71e5c6fd0bd2" xlink:to="loc_us-gaap_InventoryCurrentTable_bfceab2f-3180-43c6-82d5-9923cb89a9f6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_ca6ac666-13c3-4bf2-b212-54baa20a8862" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InventoryCurrentTable_bfceab2f-3180-43c6-82d5-9923cb89a9f6" xlink:to="loc_dei_LegalEntityAxis_ca6ac666-13c3-4bf2-b212-54baa20a8862" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_ca6ac666-13c3-4bf2-b212-54baa20a8862_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_ca6ac666-13c3-4bf2-b212-54baa20a8862" xlink:to="loc_dei_EntityDomain_ca6ac666-13c3-4bf2-b212-54baa20a8862_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0b4c2585-11c7-4f9d-832c-ce97ef5f7bec" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_ca6ac666-13c3-4bf2-b212-54baa20a8862" xlink:to="loc_dei_EntityDomain_0b4c2585-11c7-4f9d-832c-ce97ef5f7bec" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_5ceb3753-84da-4aa6-ac2b-d25e7bb288fa" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0b4c2585-11c7-4f9d-832c-ce97ef5f7bec" xlink:to="loc_sum_SummitMaterialsLlcMember_5ceb3753-84da-4aa6-ac2b-d25e7bb288fa" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACCRUEDEXPENSES" xlink:type="simple" xlink:href="sum-20220702.xsd#ACCRUEDEXPENSES"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACCRUEDEXPENSES" xlink:type="extended" id="id2376faab01c4fd0bbb5cb5ca888ec05_ACCRUEDEXPENSES">
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfAccruedExpensesLineItems_c13c8746-cd02-46ce-b61a-4c07c880f64b" xlink:href="sum-20220702.xsd#sum_ScheduleOfAccruedExpensesLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock_c07ea48c-cba0-4ac4-b02c-26aed47fd79e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_c13c8746-cd02-46ce-b61a-4c07c880f64b" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock_c07ea48c-cba0-4ac4-b02c-26aed47fd79e" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AccruedExpensesTable_56dffd15-9475-47e0-895b-cea195774419" xlink:href="sum-20220702.xsd#sum_AccruedExpensesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_c13c8746-cd02-46ce-b61a-4c07c880f64b" xlink:to="loc_sum_AccruedExpensesTable_56dffd15-9475-47e0-895b-cea195774419" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_5e6dfd69-6022-4c41-9bdc-38dc258a9dea" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_AccruedExpensesTable_56dffd15-9475-47e0-895b-cea195774419" xlink:to="loc_dei_LegalEntityAxis_5e6dfd69-6022-4c41-9bdc-38dc258a9dea" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5e6dfd69-6022-4c41-9bdc-38dc258a9dea_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_5e6dfd69-6022-4c41-9bdc-38dc258a9dea" xlink:to="loc_dei_EntityDomain_5e6dfd69-6022-4c41-9bdc-38dc258a9dea_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_39a244c6-b05c-4f1a-88c9-1333a8972077" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_5e6dfd69-6022-4c41-9bdc-38dc258a9dea" xlink:to="loc_dei_EntityDomain_39a244c6-b05c-4f1a-88c9-1333a8972077" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_58afbdd9-b94f-43f7-8cf3-75bf9f4e79f1" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_39a244c6-b05c-4f1a-88c9-1333a8972077" xlink:to="loc_sum_SummitMaterialsLlcMember_58afbdd9-b94f-43f7-8cf3-75bf9f4e79f1" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACCRUEDEXPENSESTables" xlink:type="simple" xlink:href="sum-20220702.xsd#ACCRUEDEXPENSESTables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACCRUEDEXPENSESTables" xlink:type="extended" id="i25e8c832e2a945d2a1673bb4a65b3057_ACCRUEDEXPENSESTables">
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfAccruedExpensesLineItems_ee84f8d5-6ea4-430e-8f05-f8b0ec81dd1e" xlink:href="sum-20220702.xsd#sum_ScheduleOfAccruedExpensesLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_5b6757fc-0211-4753-8568-c5a4722e64e9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_ee84f8d5-6ea4-430e-8f05-f8b0ec81dd1e" xlink:to="loc_us-gaap_ScheduleOfAccruedLiabilitiesTableTextBlock_5b6757fc-0211-4753-8568-c5a4722e64e9" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AccruedExpensesTable_b47b1814-3d15-4895-960c-ff756152e98c" xlink:href="sum-20220702.xsd#sum_AccruedExpensesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_ee84f8d5-6ea4-430e-8f05-f8b0ec81dd1e" xlink:to="loc_sum_AccruedExpensesTable_b47b1814-3d15-4895-960c-ff756152e98c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_33e8b70e-be1f-4804-9168-516d33fecfc0" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_AccruedExpensesTable_b47b1814-3d15-4895-960c-ff756152e98c" xlink:to="loc_dei_LegalEntityAxis_33e8b70e-be1f-4804-9168-516d33fecfc0" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_33e8b70e-be1f-4804-9168-516d33fecfc0_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_33e8b70e-be1f-4804-9168-516d33fecfc0" xlink:to="loc_dei_EntityDomain_33e8b70e-be1f-4804-9168-516d33fecfc0_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_df083d5a-3c97-4044-99a8-f7ba81715bb3" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_33e8b70e-be1f-4804-9168-516d33fecfc0" xlink:to="loc_dei_EntityDomain_df083d5a-3c97-4044-99a8-f7ba81715bb3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_5abf32b0-d026-429e-94cf-e0415b95c380" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_df083d5a-3c97-4044-99a8-f7ba81715bb3" xlink:to="loc_sum_SummitMaterialsLlcMember_5abf32b0-d026-429e-94cf-e0415b95c380" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/ACCRUEDEXPENSESComponentsofAccruedExpensesDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#ACCRUEDEXPENSESComponentsofAccruedExpensesDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/ACCRUEDEXPENSESComponentsofAccruedExpensesDetails" xlink:type="extended" id="i44054938ba2f4044a04ac3ffde1a9f23_ACCRUEDEXPENSESComponentsofAccruedExpensesDetails">
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:href="sum-20220702.xsd#sum_ScheduleOfAccruedExpensesLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_e8b93eff-37d4-4070-81cc-ebaea4b6fe94" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestPayableCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:to="loc_us-gaap_InterestPayableCurrent_e8b93eff-37d4-4070-81cc-ebaea4b6fe94" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedEmployeeBenefitsCurrent_52dd05bc-399d-468d-842a-1d2df5de34ad" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedEmployeeBenefitsCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:to="loc_us-gaap_AccruedEmployeeBenefitsCurrent_52dd05bc-399d-468d-842a-1d2df5de34ad" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityCurrent_c30e92b8-7803-4f71-8dfe-dfb952ee1af7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:to="loc_us-gaap_FinanceLeaseLiabilityCurrent_c30e92b8-7803-4f71-8dfe-dfb952ee1af7" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedInsuranceCurrent_a56bc3c9-f7a2-4709-90c2-1b353cdda972" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedInsuranceCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:to="loc_us-gaap_AccruedInsuranceCurrent_a56bc3c9-f7a2-4709-90c2-1b353cdda972" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent_f084532f-121c-4763-baeb-de1f97a6ff27" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:to="loc_us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent_f084532f-121c-4763-baeb-de1f97a6ff27" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AccruedAssetPurchasePaymentsCurrent_7ee5e55b-65d3-4800-93dc-d99eeb188ad4" xlink:href="sum-20220702.xsd#sum_AccruedAssetPurchasePaymentsCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:to="loc_sum_AccruedAssetPurchasePaymentsCurrent_7ee5e55b-65d3-4800-93dc-d99eeb188ad4" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedProfessionalFeesCurrent_71fad04e-1fe1-4d09-8342-f222baecd60f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedProfessionalFeesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:to="loc_us-gaap_AccruedProfessionalFeesCurrent_71fad04e-1fe1-4d09-8342-f222baecd60f" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_9c3ddb4b-1ecd-4303-b8c8-44f8fcb05a5c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_9c3ddb4b-1ecd-4303-b8c8-44f8fcb05a5c" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_6e5d2435-f589-4e96-a6b4-7d379b8bf292" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_6e5d2435-f589-4e96-a6b4-7d379b8bf292" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AccruedExpensesTable_6ac167e9-ee0b-48e4-b3f0-10e5bea2a1b0" xlink:href="sum-20220702.xsd#sum_AccruedExpensesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_ScheduleOfAccruedExpensesLineItems_e6eada6e-6fae-4e93-aca5-15cb442f9a42" xlink:to="loc_sum_AccruedExpensesTable_6ac167e9-ee0b-48e4-b3f0-10e5bea2a1b0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_b30a2296-a358-4823-a932-84d95d763904" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_AccruedExpensesTable_6ac167e9-ee0b-48e4-b3f0-10e5bea2a1b0" xlink:to="loc_dei_LegalEntityAxis_b30a2296-a358-4823-a932-84d95d763904" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_b30a2296-a358-4823-a932-84d95d763904_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_b30a2296-a358-4823-a932-84d95d763904" xlink:to="loc_dei_EntityDomain_b30a2296-a358-4823-a932-84d95d763904_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5490e17d-6664-43a8-aa5a-6009be353af6" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_b30a2296-a358-4823-a932-84d95d763904" xlink:to="loc_dei_EntityDomain_5490e17d-6664-43a8-aa5a-6009be353af6" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_8105c07c-d1c1-4da2-8e70-3ff8339ddd91" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5490e17d-6664-43a8-aa5a-6009be353af6" xlink:to="loc_sum_SummitMaterialsLlcMember_8105c07c-d1c1-4da2-8e70-3ff8339ddd91" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/DEBT" xlink:type="simple" xlink:href="sum-20220702.xsd#DEBT"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/DEBT" xlink:type="extended" id="ica7cbe00aae747d08f43f7d998233a5f_DEBT">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_5c387c8a-1566-4624-a152-ba0083fac5be" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtDisclosureTextBlock_0919342e-d9c3-4439-8e5c-d0cd9c8491c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtDisclosureTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5c387c8a-1566-4624-a152-ba0083fac5be" xlink:to="loc_us-gaap_DebtDisclosureTextBlock_0919342e-d9c3-4439-8e5c-d0cd9c8491c6" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_40b1d615-804b-4209-bc00-cc49c00c34d0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5c387c8a-1566-4624-a152-ba0083fac5be" xlink:to="loc_us-gaap_DebtInstrumentTable_40b1d615-804b-4209-bc00-cc49c00c34d0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_785b5bb4-bfd0-4789-833e-6f778e702ed2" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_40b1d615-804b-4209-bc00-cc49c00c34d0" xlink:to="loc_dei_LegalEntityAxis_785b5bb4-bfd0-4789-833e-6f778e702ed2" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_785b5bb4-bfd0-4789-833e-6f778e702ed2_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_785b5bb4-bfd0-4789-833e-6f778e702ed2" xlink:to="loc_dei_EntityDomain_785b5bb4-bfd0-4789-833e-6f778e702ed2_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_14d98e48-ee43-4c00-8271-9937e15abadb" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_785b5bb4-bfd0-4789-833e-6f778e702ed2" xlink:to="loc_dei_EntityDomain_14d98e48-ee43-4c00-8271-9937e15abadb" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_ece3999d-0dd2-4a11-9060-3fefb2ea7b2c" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_14d98e48-ee43-4c00-8271-9937e15abadb" xlink:to="loc_sum_SummitMaterialsLlcMember_ece3999d-0dd2-4a11-9060-3fefb2ea7b2c" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/DEBTTables" xlink:type="simple" xlink:href="sum-20220702.xsd#DEBTTables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/DEBTTables" xlink:type="extended" id="idabfdbbdd9e34ea8bcd1bafdfd3e56e8_DEBTTables">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_45cffca0-2835-4dbb-81a5-67efff1a201c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDebtTableTextBlock_87dfc131-9aa9-4660-b8a4-15d571377ed6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfDebtTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_45cffca0-2835-4dbb-81a5-67efff1a201c" xlink:to="loc_us-gaap_ScheduleOfDebtTableTextBlock_87dfc131-9aa9-4660-b8a4-15d571377ed6" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfMaturitiesOfLongTermDebtTableTextBlock_9400097b-2325-46f9-9351-295d160d3733" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfMaturitiesOfLongTermDebtTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_45cffca0-2835-4dbb-81a5-67efff1a201c" xlink:to="loc_us-gaap_ScheduleOfMaturitiesOfLongTermDebtTableTextBlock_9400097b-2325-46f9-9351-295d160d3733" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfDeferredFinancingFeesTableTextBlock_f3470542-2c28-4bb3-9776-86daf0f2691e" xlink:href="sum-20220702.xsd#sum_ScheduleOfDeferredFinancingFeesTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_45cffca0-2835-4dbb-81a5-67efff1a201c" xlink:to="loc_sum_ScheduleOfDeferredFinancingFeesTableTextBlock_f3470542-2c28-4bb3-9776-86daf0f2691e" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_39cf6fd6-76d8-4a2e-b3e3-8f841865930e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_45cffca0-2835-4dbb-81a5-67efff1a201c" xlink:to="loc_us-gaap_DebtInstrumentTable_39cf6fd6-76d8-4a2e-b3e3-8f841865930e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_0ee4c5d3-f9a0-4008-be89-e7552101dffd" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_39cf6fd6-76d8-4a2e-b3e3-8f841865930e" xlink:to="loc_dei_LegalEntityAxis_0ee4c5d3-f9a0-4008-be89-e7552101dffd" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0ee4c5d3-f9a0-4008-be89-e7552101dffd_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_0ee4c5d3-f9a0-4008-be89-e7552101dffd" xlink:to="loc_dei_EntityDomain_0ee4c5d3-f9a0-4008-be89-e7552101dffd_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a079ec2c-4261-4f70-9c14-994fc6e112f3" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_0ee4c5d3-f9a0-4008-be89-e7552101dffd" xlink:to="loc_dei_EntityDomain_a079ec2c-4261-4f70-9c14-994fc6e112f3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_fbdbae23-1566-498c-8556-8685be87bbc9" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a079ec2c-4261-4f70-9c14-994fc6e112f3" xlink:to="loc_sum_SummitMaterialsLlcMember_fbdbae23-1566-498c-8556-8685be87bbc9" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/DEBTScheduleofDebtDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#DEBTScheduleofDebtDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/DEBTScheduleofDebtDetails" xlink:type="extended" id="i631ecb249cfe46bdb7d4766c91c06fce_DEBTScheduleofDebtDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_4e72e065-c482-4942-8143-80550721834e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_b9c3121d-abc8-4003-80f9-f380c726e894" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4e72e065-c482-4942-8143-80550721834e" xlink:to="loc_us-gaap_LongTermDebt_b9c3121d-abc8-4003-80f9-f380c726e894" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_485fa314-3181-4ab1-b913-4851a3facdb6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4e72e065-c482-4942-8143-80550721834e" xlink:to="loc_us-gaap_LongTermDebtCurrent_485fa314-3181-4ab1-b913-4851a3facdb6" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_becb6113-02f2-4cb3-98ec-821a083d4655" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4e72e065-c482-4942-8143-80550721834e" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_becb6113-02f2-4cb3-98ec-821a083d4655" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_33212f0c-0e4f-49f7-b591-1e1a85969180" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4e72e065-c482-4942-8143-80550721834e" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_33212f0c-0e4f-49f7-b591-1e1a85969180" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_92776ce4-2005-4ade-a54a-eb3a92d83000" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4e72e065-c482-4942-8143-80550721834e" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_92776ce4-2005-4ade-a54a-eb3a92d83000" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_e4e92667-96ff-4837-8822-370bed0ddee5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4e72e065-c482-4942-8143-80550721834e" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_e4e92667-96ff-4837-8822-370bed0ddee5" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_a2468242-592a-4c9f-9d2e-c863f5b6616d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4e72e065-c482-4942-8143-80550721834e" xlink:to="loc_us-gaap_DebtInstrumentTable_a2468242-592a-4c9f-9d2e-c863f5b6616d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_cb843feb-0c2b-45e1-ae2b-2a919fb0983b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a2468242-592a-4c9f-9d2e-c863f5b6616d" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_cb843feb-0c2b-45e1-ae2b-2a919fb0983b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_cb843feb-0c2b-45e1-ae2b-2a919fb0983b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_cb843feb-0c2b-45e1-ae2b-2a919fb0983b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_cb843feb-0c2b-45e1-ae2b-2a919fb0983b_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_fa36b81a-64e8-4285-b53c-fe87ad3bddbd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_cb843feb-0c2b-45e1-ae2b-2a919fb0983b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_fa36b81a-64e8-4285-b53c-fe87ad3bddbd" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_bbda5cb8-da7e-4415-a89c-58c41fdb01e2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SeniorNotesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_fa36b81a-64e8-4285-b53c-fe87ad3bddbd" xlink:to="loc_us-gaap_SeniorNotesMember_bbda5cb8-da7e-4415-a89c-58c41fdb01e2" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_0d6c773c-9c89-413f-acca-b2e6459c8023" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a2468242-592a-4c9f-9d2e-c863f5b6616d" xlink:to="loc_dei_LegalEntityAxis_0d6c773c-9c89-413f-acca-b2e6459c8023" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0d6c773c-9c89-413f-acca-b2e6459c8023_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_0d6c773c-9c89-413f-acca-b2e6459c8023" xlink:to="loc_dei_EntityDomain_0d6c773c-9c89-413f-acca-b2e6459c8023_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_8217ada3-6d4b-446d-a08a-95c37d7d1237" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_0d6c773c-9c89-413f-acca-b2e6459c8023" xlink:to="loc_dei_EntityDomain_8217ada3-6d4b-446d-a08a-95c37d7d1237" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_25ec58fe-8b33-41aa-a27a-5c8fa5946b9d" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_8217ada3-6d4b-446d-a08a-95c37d7d1237" xlink:to="loc_sum_SummitMaterialsLlcMember_25ec58fe-8b33-41aa-a27a-5c8fa5946b9d" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_cdf43562-4355-4dc4-b87a-85c1e79fc4df" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a2468242-592a-4c9f-9d2e-c863f5b6616d" xlink:to="loc_us-gaap_DebtInstrumentAxis_cdf43562-4355-4dc4-b87a-85c1e79fc4df" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_cdf43562-4355-4dc4-b87a-85c1e79fc4df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_cdf43562-4355-4dc4-b87a-85c1e79fc4df" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_cdf43562-4355-4dc4-b87a-85c1e79fc4df_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_33a04f3d-1089-4024-9322-87d43f7dd150" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_cdf43562-4355-4dc4-b87a-85c1e79fc4df" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_33a04f3d-1089-4024-9322-87d43f7dd150" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SeniorSecuredCreditFacilityTermLoanDueTwoThousandTwentyFourMember_afcc2a29-7209-45a4-a05f-d3336eb6f632" xlink:href="sum-20220702.xsd#sum_SeniorSecuredCreditFacilityTermLoanDueTwoThousandTwentyFourMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_33a04f3d-1089-4024-9322-87d43f7dd150" xlink:to="loc_sum_SeniorSecuredCreditFacilityTermLoanDueTwoThousandTwentyFourMember_afcc2a29-7209-45a4-a05f-d3336eb6f632" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SixPointFivePercentageSeniorNotesDueTwentyTwentySevenMember_94901f10-f412-45db-b0fe-46a8e413d8db" xlink:href="sum-20220702.xsd#sum_SixPointFivePercentageSeniorNotesDueTwentyTwentySevenMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_33a04f3d-1089-4024-9322-87d43f7dd150" xlink:to="loc_sum_SixPointFivePercentageSeniorNotesDueTwentyTwentySevenMember_94901f10-f412-45db-b0fe-46a8e413d8db" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_FivePointTwoFivePercentageSeniorNotesDueTwentyTwentyNineMember_1d2c7505-ccde-4aee-a519-cca1dc035149" xlink:href="sum-20220702.xsd#sum_FivePointTwoFivePercentageSeniorNotesDueTwentyTwentyNineMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_33a04f3d-1089-4024-9322-87d43f7dd150" xlink:to="loc_sum_FivePointTwoFivePercentageSeniorNotesDueTwentyTwentyNineMember_1d2c7505-ccde-4aee-a519-cca1dc035149" xlink:type="arc" order="2"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/DEBTScheduleofContractualPaymentsofLongTermDebtDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#DEBTScheduleofContractualPaymentsofLongTermDebtDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/DEBTScheduleofContractualPaymentsofLongTermDebtDetails" xlink:type="extended" id="i7b7f97be04774bae995f634c43c3441e_DEBTScheduleofContractualPaymentsofLongTermDebtDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_a9bffa11-e079-40b7-95b7-e99cc7ab24c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_a9bffa11-e079-40b7-95b7-e99cc7ab24c3" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_b0f215e8-9e28-4670-b93a-7fe187e03857" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_b0f215e8-9e28-4670-b93a-7fe187e03857" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_9c79cdb2-a784-49b3-bb36-2f80c1d3d459" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_9c79cdb2-a784-49b3-bb36-2f80c1d3d459" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_69a489c0-68d2-486d-9d5f-f1f88abc5aac" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_69a489c0-68d2-486d-9d5f-f1f88abc5aac" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_349c2df2-abc4-47ff-952d-12bbc7afcd68" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_349c2df2-abc4-47ff-952d-12bbc7afcd68" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_6cf1e9d8-128e-43d8-ac62-27ea82df26dd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_6cf1e9d8-128e-43d8-ac62-27ea82df26dd" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_a37ebc7d-c1eb-4f88-8c11-5871815bcf4f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive_a37ebc7d-c1eb-4f88-8c11-5871815bcf4f" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_60574875-79e2-457f-903c-b472ee3db7f2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_60574875-79e2-457f-903c-b472ee3db7f2" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_5b690eae-1676-41eb-a0ad-92243f9f1ce6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_5b690eae-1676-41eb-a0ad-92243f9f1ce6" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCostsCurrentAndNoncurrent_780f195e-a648-4b8f-88e6-383c68cb2851" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredCostsCurrentAndNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_DeferredCostsCurrentAndNoncurrent_780f195e-a648-4b8f-88e6-383c68cb2851" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_LongTermDebtNet_6bca5107-7a7b-4487-91c9-bf728245b32e" xlink:href="sum-20220702.xsd#sum_LongTermDebtNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_sum_LongTermDebtNet_6bca5107-7a7b-4487-91c9-bf728245b32e" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_a9d308ac-ed44-4572-8264-591fda72465c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_f46f6ae9-5463-406a-badf-4b77dc203754" xlink:to="loc_us-gaap_DebtInstrumentTable_a9d308ac-ed44-4572-8264-591fda72465c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_d53e4b96-3173-4254-aa4c-421f42d7111f" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a9d308ac-ed44-4572-8264-591fda72465c" xlink:to="loc_dei_LegalEntityAxis_d53e4b96-3173-4254-aa4c-421f42d7111f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_d53e4b96-3173-4254-aa4c-421f42d7111f_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_d53e4b96-3173-4254-aa4c-421f42d7111f" xlink:to="loc_dei_EntityDomain_d53e4b96-3173-4254-aa4c-421f42d7111f_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_b3823e4d-9ed3-4791-871c-5d50b6428590" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_d53e4b96-3173-4254-aa4c-421f42d7111f" xlink:to="loc_dei_EntityDomain_b3823e4d-9ed3-4791-871c-5d50b6428590" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_65dd707b-6edf-430c-8968-768f6c364803" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_b3823e4d-9ed3-4791-871c-5d50b6428590" xlink:to="loc_sum_SummitMaterialsLlcMember_65dd707b-6edf-430c-8968-768f6c364803" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/DEBTSeniorNotesDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#DEBTSeniorNotesDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/DEBTSeniorNotesDetails" xlink:type="extended" id="i25f5d16bf98d47a584048d2570c06d56_DEBTSeniorNotesDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_a4b39136-cd83-4556-b889-b9fd7a37c668" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_42118915-771e-4560-9a02-f80a01e0f0b6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a4b39136-cd83-4556-b889-b9fd7a37c668" xlink:to="loc_us-gaap_LongTermDebt_42118915-771e-4560-9a02-f80a01e0f0b6" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_1babaee2-b3ae-4c23-a0c5-c69656669bc1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a4b39136-cd83-4556-b889-b9fd7a37c668" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_1babaee2-b3ae-4c23-a0c5-c69656669bc1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_PercentageOfParValueOnSeniorNotes_07ba23c5-7b6e-4f6f-b194-0610d4e8267d" xlink:href="sum-20220702.xsd#sum_PercentageOfParValueOnSeniorNotes"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a4b39136-cd83-4556-b889-b9fd7a37c668" xlink:to="loc_sum_PercentageOfParValueOnSeniorNotes_07ba23c5-7b6e-4f6f-b194-0610d4e8267d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_96eb26fe-b73f-48f0-890b-1ee3c7099b55" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a4b39136-cd83-4556-b889-b9fd7a37c668" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_96eb26fe-b73f-48f0-890b-1ee3c7099b55" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDebtNetOfIssuanceCosts_bbd1f6ad-455d-4b98-a292-b6138deb0b08" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromDebtNetOfIssuanceCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a4b39136-cd83-4556-b889-b9fd7a37c668" xlink:to="loc_us-gaap_ProceedsFromDebtNetOfIssuanceCosts_bbd1f6ad-455d-4b98-a292-b6138deb0b08" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_d9e8c6d6-665a-4a92-9d9e-37f3a826e23d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a4b39136-cd83-4556-b889-b9fd7a37c668" xlink:to="loc_us-gaap_DebtInstrumentTable_d9e8c6d6-665a-4a92-9d9e-37f3a826e23d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_8bb49f8b-ab28-4b58-bb29-87696beb513c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_d9e8c6d6-665a-4a92-9d9e-37f3a826e23d" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_8bb49f8b-ab28-4b58-bb29-87696beb513c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_8bb49f8b-ab28-4b58-bb29-87696beb513c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_8bb49f8b-ab28-4b58-bb29-87696beb513c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_8bb49f8b-ab28-4b58-bb29-87696beb513c_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c2716851-65a2-40a9-b9ae-86b6b53b0e7c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_8bb49f8b-ab28-4b58-bb29-87696beb513c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c2716851-65a2-40a9-b9ae-86b6b53b0e7c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_ea5940dd-efee-4afc-8192-5b848ba8f615" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SeniorNotesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_c2716851-65a2-40a9-b9ae-86b6b53b0e7c" xlink:to="loc_us-gaap_SeniorNotesMember_ea5940dd-efee-4afc-8192-5b848ba8f615" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_6bbaea51-2a0b-4aba-9a3f-eb47ffc30888" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_d9e8c6d6-665a-4a92-9d9e-37f3a826e23d" xlink:to="loc_dei_LegalEntityAxis_6bbaea51-2a0b-4aba-9a3f-eb47ffc30888" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_6bbaea51-2a0b-4aba-9a3f-eb47ffc30888_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_6bbaea51-2a0b-4aba-9a3f-eb47ffc30888" xlink:to="loc_dei_EntityDomain_6bbaea51-2a0b-4aba-9a3f-eb47ffc30888_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_d75d026e-4f0a-4e4e-b0b2-2e52e511b228" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_6bbaea51-2a0b-4aba-9a3f-eb47ffc30888" xlink:to="loc_dei_EntityDomain_d75d026e-4f0a-4e4e-b0b2-2e52e511b228" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcAndSummitMaterialsFinanceCorpMember_acadc13e-a9a1-49d4-8760-251a85f52eb0" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcAndSummitMaterialsFinanceCorpMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_d75d026e-4f0a-4e4e-b0b2-2e52e511b228" xlink:to="loc_sum_SummitMaterialsLlcAndSummitMaterialsFinanceCorpMember_acadc13e-a9a1-49d4-8760-251a85f52eb0" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_f41f2c27-d96d-45b4-85db-9f17b4b2c2e5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_d9e8c6d6-665a-4a92-9d9e-37f3a826e23d" xlink:to="loc_us-gaap_DebtInstrumentAxis_f41f2c27-d96d-45b4-85db-9f17b4b2c2e5" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_f41f2c27-d96d-45b4-85db-9f17b4b2c2e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_f41f2c27-d96d-45b4-85db-9f17b4b2c2e5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_f41f2c27-d96d-45b4-85db-9f17b4b2c2e5_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_0d71f2a9-1cd0-4f17-a4fb-32c078d0f060" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_f41f2c27-d96d-45b4-85db-9f17b4b2c2e5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_0d71f2a9-1cd0-4f17-a4fb-32c078d0f060" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_FivePointTwoFivePercentageSeniorNotesDueTwentyTwentyNineMember_56bea520-d07d-47a6-b7f7-0c69273e5f31" xlink:href="sum-20220702.xsd#sum_FivePointTwoFivePercentageSeniorNotesDueTwentyTwentyNineMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_0d71f2a9-1cd0-4f17-a4fb-32c078d0f060" xlink:to="loc_sum_FivePointTwoFivePercentageSeniorNotesDueTwentyTwentyNineMember_56bea520-d07d-47a6-b7f7-0c69273e5f31" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SixPointFivePercentageSeniorNotesDueTwentyTwentySevenMember_608168c8-0487-4ef9-8091-3485115eeaf1" xlink:href="sum-20220702.xsd#sum_SixPointFivePercentageSeniorNotesDueTwentyTwentySevenMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_0d71f2a9-1cd0-4f17-a4fb-32c078d0f060" xlink:to="loc_sum_SixPointFivePercentageSeniorNotesDueTwentyTwentySevenMember_608168c8-0487-4ef9-8091-3485115eeaf1" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/DEBTSeniorSecuredCreditFacilitiesDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#DEBTSeniorSecuredCreditFacilitiesDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/DEBTSeniorSecuredCreditFacilitiesDetails" xlink:type="extended" id="i1990dc9fbfb04db29ec1302ea4ae4be3_DEBTSeniorSecuredCreditFacilitiesDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_edb5efe4-d8a4-426a-8b0a-cbe6f62700f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFaceAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_edb5efe4-d8a4-426a-8b0a-cbe6f62700f3" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_69ffad44-5772-4c9d-adf9-1d710d76776b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_69ffad44-5772-4c9d-adf9-1d710d76776b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_DebtInstrumentQuarterlyPrincipalRepaymentPercentage_012c1575-9874-496a-9fc8-a3a35f53d9c4" xlink:href="sum-20220702.xsd#sum_DebtInstrumentQuarterlyPrincipalRepaymentPercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_sum_DebtInstrumentQuarterlyPrincipalRepaymentPercentage_012c1575-9874-496a-9fc8-a3a35f53d9c4" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfDebt_1f457c93-8606-44d0-8e13-9eff8cfe0d22" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_us-gaap_RepaymentsOfDebt_1f457c93-8606-44d0-8e13-9eff8cfe0d22" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_9b37c73b-223a-42c9-b9a6-aabcdf7604fa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_9b37c73b-223a-42c9-b9a6-aabcdf7604fa" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_e1a565e5-e226-4abe-b86d-ee2ba2365c8d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_e1a565e5-e226-4abe-b86d-ee2ba2365c8d" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_DebtInstrumentReferenceRateAdditionalPercentage_bb1bf3cd-05a5-4986-a990-2199baf2fe99" xlink:href="sum-20220702.xsd#sum_DebtInstrumentReferenceRateAdditionalPercentage"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_sum_DebtInstrumentReferenceRateAdditionalPercentage_bb1bf3cd-05a5-4986-a990-2199baf2fe99" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_1db38361-4816-48a2-a5bc-be0b22153e66" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCredit"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_us-gaap_LineOfCredit_1db38361-4816-48a2-a5bc-be0b22153e66" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_59cfdf2c-5649-431c-aec6-17622ff028fd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_59cfdf2c-5649-431c-aec6-17622ff028fd" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_FirstLienLeverageRatio_e8fa8fc2-cde8-4569-be7f-a3878a9bca32" xlink:href="sum-20220702.xsd#sum_FirstLienLeverageRatio"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_sum_FirstLienLeverageRatio_e8fa8fc2-cde8-4569-be7f-a3878a9bca32" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_3640f27d-654e-4c37-9691-8f1b0c18d931" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_60a78234-d561-4494-8e69-3b8fa799fca6" xlink:to="loc_us-gaap_DebtInstrumentTable_3640f27d-654e-4c37-9691-8f1b0c18d931" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_56b4a523-0133-4eca-a741-9f2158d9987a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_3640f27d-654e-4c37-9691-8f1b0c18d931" xlink:to="loc_us-gaap_DebtInstrumentAxis_56b4a523-0133-4eca-a741-9f2158d9987a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_56b4a523-0133-4eca-a741-9f2158d9987a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_56b4a523-0133-4eca-a741-9f2158d9987a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_56b4a523-0133-4eca-a741-9f2158d9987a_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ff55799d-95a6-4583-aa22-7f72d75f872b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_56b4a523-0133-4eca-a741-9f2158d9987a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ff55799d-95a6-4583-aa22-7f72d75f872b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SeniorSecuredCreditFacilityTermLoanDueTwoThousandTwentyFourMember_0c26e82d-164a-4c17-924f-508edd76ddfe" xlink:href="sum-20220702.xsd#sum_SeniorSecuredCreditFacilityTermLoanDueTwoThousandTwentyFourMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ff55799d-95a6-4583-aa22-7f72d75f872b" xlink:to="loc_sum_SeniorSecuredCreditFacilityTermLoanDueTwoThousandTwentyFourMember_0c26e82d-164a-4c17-924f-508edd76ddfe" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SeniorSecuredCreditFacilityRevolvingCreditFacilityMember_692bc278-909b-46ce-9a72-df937ebedab5" xlink:href="sum-20220702.xsd#sum_SeniorSecuredCreditFacilityRevolvingCreditFacilityMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ff55799d-95a6-4583-aa22-7f72d75f872b" xlink:to="loc_sum_SeniorSecuredCreditFacilityRevolvingCreditFacilityMember_692bc278-909b-46ce-9a72-df937ebedab5" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SeniorSecuredCreditFacilityLetterOfCreditMember_13ff5b02-ae27-4c2f-a647-74bb50ced5bd" xlink:href="sum-20220702.xsd#sum_SeniorSecuredCreditFacilityLetterOfCreditMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ff55799d-95a6-4583-aa22-7f72d75f872b" xlink:to="loc_sum_SeniorSecuredCreditFacilityLetterOfCreditMember_13ff5b02-ae27-4c2f-a647-74bb50ced5bd" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SeniorSecuredCreditFacilitiesMember_25730700-81e5-4824-8e72-36ab915e4197" xlink:href="sum-20220702.xsd#sum_SeniorSecuredCreditFacilitiesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ff55799d-95a6-4583-aa22-7f72d75f872b" xlink:to="loc_sum_SeniorSecuredCreditFacilitiesMember_25730700-81e5-4824-8e72-36ab915e4197" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_cd295d83-50e3-46ad-97e5-f89d911f9342" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_3640f27d-654e-4c37-9691-8f1b0c18d931" xlink:to="loc_dei_LegalEntityAxis_cd295d83-50e3-46ad-97e5-f89d911f9342" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_cd295d83-50e3-46ad-97e5-f89d911f9342_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_cd295d83-50e3-46ad-97e5-f89d911f9342" xlink:to="loc_dei_EntityDomain_cd295d83-50e3-46ad-97e5-f89d911f9342_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e450ed7f-cef1-4d22-a807-e3ec6b2546e6" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_cd295d83-50e3-46ad-97e5-f89d911f9342" xlink:to="loc_dei_EntityDomain_e450ed7f-cef1-4d22-a807-e3ec6b2546e6" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_4e898e68-b7d6-4f4e-a8c4-944ad63cd926" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_e450ed7f-cef1-4d22-a807-e3ec6b2546e6" xlink:to="loc_sum_SummitMaterialsLlcMember_4e898e68-b7d6-4f4e-a8c4-944ad63cd926" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_cab300dd-b645-4848-a085-b9147ad35a47" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_3640f27d-654e-4c37-9691-8f1b0c18d931" xlink:to="loc_us-gaap_VariableRateAxis_cab300dd-b645-4848-a085-b9147ad35a47" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_cab300dd-b645-4848-a085-b9147ad35a47_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_cab300dd-b645-4848-a085-b9147ad35a47" xlink:to="loc_us-gaap_VariableRateDomain_cab300dd-b645-4848-a085-b9147ad35a47_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_ce1cf382-8f3c-4d30-a8e2-6921073d3c02" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_cab300dd-b645-4848-a085-b9147ad35a47" xlink:to="loc_us-gaap_VariableRateDomain_ce1cf382-8f3c-4d30-a8e2-6921073d3c02" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_FederalFundsEffectiveRateMember_f6ff4c0b-c4cf-4690-93c0-f60f999acc92" xlink:href="sum-20220702.xsd#sum_FederalFundsEffectiveRateMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_ce1cf382-8f3c-4d30-a8e2-6921073d3c02" xlink:to="loc_sum_FederalFundsEffectiveRateMember_f6ff4c0b-c4cf-4690-93c0-f60f999acc92" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_LondonInterbankOfferedRateLiborPlusOnePercentMember_3646ca9b-5b35-4c86-b4fe-e1db567341c2" xlink:href="sum-20220702.xsd#sum_LondonInterbankOfferedRateLiborPlusOnePercentMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_ce1cf382-8f3c-4d30-a8e2-6921073d3c02" xlink:to="loc_sum_LondonInterbankOfferedRateLiborPlusOnePercentMember_3646ca9b-5b35-4c86-b4fe-e1db567341c2" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_fc884ef8-2bd6-4c24-8049-78c3cdd9f796" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_ce1cf382-8f3c-4d30-a8e2-6921073d3c02" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_fc884ef8-2bd6-4c24-8049-78c3cdd9f796" xlink:type="arc" order="2"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/DEBTSummaryofActivityforDeferredFinancingFeesDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#DEBTSummaryofActivityforDeferredFinancingFeesDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/DEBTSummaryofActivityforDeferredFinancingFeesDetails" xlink:type="extended" id="i78e0bf78f67147f1ac73d852a5b64588_DEBTSummaryofActivityforDeferredFinancingFeesDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_46367232-ec4f-49a4-b693-5a90fe1fa29c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsOwnshareLendingArrangementIssuanceCostsAccumulatedAmortizationRollForward_30efddf5-c14a-41d3-acfb-2efe51847587" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsOwnshareLendingArrangementIssuanceCostsAccumulatedAmortizationRollForward"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_46367232-ec4f-49a4-b693-5a90fe1fa29c" xlink:to="loc_us-gaap_DeferredFinanceCostsOwnshareLendingArrangementIssuanceCostsAccumulatedAmortizationRollForward_30efddf5-c14a-41d3-acfb-2efe51847587" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_bd7e80b8-d6e2-452e-a4ff-8aba02ba12d5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredFinanceCostsOwnshareLendingArrangementIssuanceCostsAccumulatedAmortizationRollForward_30efddf5-c14a-41d3-acfb-2efe51847587" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_bd7e80b8-d6e2-452e-a4ff-8aba02ba12d5" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_cc9aeb51-9807-4b79-9b2f-1f9348fbdbb5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfFinancingCosts"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredFinanceCostsOwnshareLendingArrangementIssuanceCostsAccumulatedAmortizationRollForward_30efddf5-c14a-41d3-acfb-2efe51847587" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_cc9aeb51-9807-4b79-9b2f-1f9348fbdbb5" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_194df7ba-4c07-4686-abf4-5d3fd265dc21" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredFinanceCostsNet"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_210029bb-7d34-47dd-89f2-24b5f602df74" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_46367232-ec4f-49a4-b693-5a90fe1fa29c" xlink:to="loc_us-gaap_DebtInstrumentTable_210029bb-7d34-47dd-89f2-24b5f602df74" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_7397ca5b-a91b-4fa3-9f95-b2d1bb65d571" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_210029bb-7d34-47dd-89f2-24b5f602df74" xlink:to="loc_dei_LegalEntityAxis_7397ca5b-a91b-4fa3-9f95-b2d1bb65d571" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_7397ca5b-a91b-4fa3-9f95-b2d1bb65d571_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_7397ca5b-a91b-4fa3-9f95-b2d1bb65d571" xlink:to="loc_dei_EntityDomain_7397ca5b-a91b-4fa3-9f95-b2d1bb65d571_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_b216d115-9e4c-41d4-8650-770412506f2a" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_7397ca5b-a91b-4fa3-9f95-b2d1bb65d571" xlink:to="loc_dei_EntityDomain_b216d115-9e4c-41d4-8650-770412506f2a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_4f6e5805-91b0-47a5-8033-8df99f2dbc7d" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_b216d115-9e4c-41d4-8650-770412506f2a" xlink:to="loc_sum_SummitMaterialsLlcMember_4f6e5805-91b0-47a5-8033-8df99f2dbc7d" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/DEBTOtherDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#DEBTOtherDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/DEBTOtherDetails" xlink:type="extended" id="ib3d784f7bffb41daa85cb0ca117fc971_DEBTOtherDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_af99a845-6e92-4874-9729-54b5d3ea1952" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_ec1e531a-b824-4885-b1b9-13fe42221565" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_af99a845-6e92-4874-9729-54b5d3ea1952" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_ec1e531a-b824-4885-b1b9-13fe42221565" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_e46ca939-8e91-498c-8414-0a35bc98343e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_af99a845-6e92-4874-9729-54b5d3ea1952" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_e46ca939-8e91-498c-8414-0a35bc98343e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_864f9219-dd00-4871-b8aa-82d4424b6b2d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LineOfCredit"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_af99a845-6e92-4874-9729-54b5d3ea1952" xlink:to="loc_us-gaap_LineOfCredit_864f9219-dd00-4871-b8aa-82d4424b6b2d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_17e0ec35-f793-41f3-bf80-52289bff3f34" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_af99a845-6e92-4874-9729-54b5d3ea1952" xlink:to="loc_us-gaap_DebtInstrumentTable_17e0ec35-f793-41f3-bf80-52289bff3f34" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_745dfc20-1851-43ea-9004-14fe9e2405de" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_17e0ec35-f793-41f3-bf80-52289bff3f34" xlink:to="loc_dei_LegalEntityAxis_745dfc20-1851-43ea-9004-14fe9e2405de" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_745dfc20-1851-43ea-9004-14fe9e2405de_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_745dfc20-1851-43ea-9004-14fe9e2405de" xlink:to="loc_dei_EntityDomain_745dfc20-1851-43ea-9004-14fe9e2405de_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_91a23945-1e84-496c-b397-4cce177db28e" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_745dfc20-1851-43ea-9004-14fe9e2405de" xlink:to="loc_dei_EntityDomain_91a23945-1e84-496c-b397-4cce177db28e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_e11b2881-7ff6-4cc9-9c75-d5438e43650e" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_91a23945-1e84-496c-b397-4cce177db28e" xlink:to="loc_sum_SummitMaterialsLlcMember_e11b2881-7ff6-4cc9-9c75-d5438e43650e" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_d2adbd01-12bf-4931-ac10-3acf431763b7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_17e0ec35-f793-41f3-bf80-52289bff3f34" xlink:to="loc_us-gaap_VariableRateAxis_d2adbd01-12bf-4931-ac10-3acf431763b7" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_d2adbd01-12bf-4931-ac10-3acf431763b7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_d2adbd01-12bf-4931-ac10-3acf431763b7" xlink:to="loc_us-gaap_VariableRateDomain_d2adbd01-12bf-4931-ac10-3acf431763b7_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_92d420f6-2ccf-4f15-a303-f81acf483b5b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_d2adbd01-12bf-4931-ac10-3acf431763b7" xlink:to="loc_us-gaap_VariableRateDomain_92d420f6-2ccf-4f15-a303-f81acf483b5b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrimeRateMember_9b473821-4b04-46d5-bd40-f36bcea023fa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PrimeRateMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_92d420f6-2ccf-4f15-a303-f81acf483b5b" xlink:to="loc_us-gaap_PrimeRateMember_9b473821-4b04-46d5-bd40-f36bcea023fa" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_46b383e1-97ca-42ac-ad77-ca799a82cb18" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_17e0ec35-f793-41f3-bf80-52289bff3f34" xlink:to="loc_us-gaap_DebtInstrumentAxis_46b383e1-97ca-42ac-ad77-ca799a82cb18" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_46b383e1-97ca-42ac-ad77-ca799a82cb18_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_46b383e1-97ca-42ac-ad77-ca799a82cb18" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_46b383e1-97ca-42ac-ad77-ca799a82cb18_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_d2e8bce1-a63b-445b-a15c-269701302c64" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_46b383e1-97ca-42ac-ad77-ca799a82cb18" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_d2e8bce1-a63b-445b-a15c-269701302c64" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CanadianSubsidiaryCreditAgreementOperatingActivitiesMember_fc7e5ec5-a554-4516-ba27-0aa9a8900a55" xlink:href="sum-20220702.xsd#sum_CanadianSubsidiaryCreditAgreementOperatingActivitiesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d2e8bce1-a63b-445b-a15c-269701302c64" xlink:to="loc_sum_CanadianSubsidiaryCreditAgreementOperatingActivitiesMember_fc7e5ec5-a554-4516-ba27-0aa9a8900a55" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CanadianSubsidiaryCreditAgreementCapitalEquipmentMember_2b564982-97bd-488e-8975-0cdd14324e78" xlink:href="sum-20220702.xsd#sum_CanadianSubsidiaryCreditAgreementCapitalEquipmentMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d2e8bce1-a63b-445b-a15c-269701302c64" xlink:to="loc_sum_CanadianSubsidiaryCreditAgreementCapitalEquipmentMember_2b564982-97bd-488e-8975-0cdd14324e78" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CanadianSubsidiaryCreditAgreementGuaranteesMember_003a4f2f-d482-417e-84ef-670fdf46b322" xlink:href="sum-20220702.xsd#sum_CanadianSubsidiaryCreditAgreementGuaranteesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d2e8bce1-a63b-445b-a15c-269701302c64" xlink:to="loc_sum_CanadianSubsidiaryCreditAgreementGuaranteesMember_003a4f2f-d482-417e-84ef-670fdf46b322" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CanadianSubsidiaryCreditAgreementMember_7c109b6f-9dfd-4e29-8f05-29896c0e836e" xlink:href="sum-20220702.xsd#sum_CanadianSubsidiaryCreditAgreementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d2e8bce1-a63b-445b-a15c-269701302c64" xlink:to="loc_sum_CanadianSubsidiaryCreditAgreementMember_7c109b6f-9dfd-4e29-8f05-29896c0e836e" xlink:type="arc" order="3"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/INCOMETAXES" xlink:type="simple" xlink:href="sum-20220702.xsd#INCOMETAXES"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/INCOMETAXES" xlink:type="extended" id="i909292ef6bd04f33a90b10ae32d78f94_INCOMETAXES">
<link:loc xlink:type="locator" xlink:label="loc_sum_IncomeTaxesLineItems_8c76124d-5f85-433a-beb3-3b6a202b995b" xlink:href="sum-20220702.xsd#sum_IncomeTaxesLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxDisclosureTextBlock_99d01b9a-08de-45e2-a727-e9341571a73c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxDisclosureTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IncomeTaxesLineItems_8c76124d-5f85-433a-beb3-3b6a202b995b" xlink:to="loc_us-gaap_IncomeTaxDisclosureTextBlock_99d01b9a-08de-45e2-a727-e9341571a73c" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_IncomeTaxesTable_8cf6f6ee-8e9f-40df-88d2-850f862f88b6" xlink:href="sum-20220702.xsd#sum_IncomeTaxesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_IncomeTaxesLineItems_8c76124d-5f85-433a-beb3-3b6a202b995b" xlink:to="loc_sum_IncomeTaxesTable_8cf6f6ee-8e9f-40df-88d2-850f862f88b6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_9b09e1aa-eae4-4b31-82a0-2049d0a3e94b" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_IncomeTaxesTable_8cf6f6ee-8e9f-40df-88d2-850f862f88b6" xlink:to="loc_dei_LegalEntityAxis_9b09e1aa-eae4-4b31-82a0-2049d0a3e94b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_9b09e1aa-eae4-4b31-82a0-2049d0a3e94b_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_9b09e1aa-eae4-4b31-82a0-2049d0a3e94b" xlink:to="loc_dei_EntityDomain_9b09e1aa-eae4-4b31-82a0-2049d0a3e94b_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a7264be6-5b20-4aea-b96b-8a66b3646c60" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_9b09e1aa-eae4-4b31-82a0-2049d0a3e94b" xlink:to="loc_dei_EntityDomain_a7264be6-5b20-4aea-b96b-8a66b3646c60" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_d456a3ed-476a-42c2-9dc2-cf2fb10c15e4" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a7264be6-5b20-4aea-b96b-8a66b3646c60" xlink:to="loc_sum_SummitMaterialsLlcMember_d456a3ed-476a-42c2-9dc2-cf2fb10c15e4" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/INCOMETAXESNarrativeDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#INCOMETAXESNarrativeDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/INCOMETAXESNarrativeDetails" xlink:type="extended" id="i417b91e4fa1a41c7a78e5f09d0fee8dd_INCOMETAXESNarrativeDetails">
<link:loc xlink:type="locator" xlink:label="loc_sum_IncomeTaxesLineItems_25794e50-5611-4d6e-b74b-277678354813" xlink:href="sum-20220702.xsd#sum_IncomeTaxesLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_25c55173-6d31-491a-9c5a-b3f01a1f7d2b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IncomeTaxesLineItems_25794e50-5611-4d6e-b74b-277678354813" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_25c55173-6d31-491a-9c5a-b3f01a1f7d2b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowance_c70e33a9-2682-4dfd-8229-942d51ffc989" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsValuationAllowance"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IncomeTaxesLineItems_25794e50-5611-4d6e-b74b-277678354813" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowance_c70e33a9-2682-4dfd-8229-942d51ffc989" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense_f7cb554e-acdc-4b6d-9e81-f084e560b7f8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IncomeTaxesLineItems_25794e50-5611-4d6e-b74b-277678354813" xlink:to="loc_us-gaap_IncomeTaxExaminationPenaltiesAndInterestExpense_f7cb554e-acdc-4b6d-9e81-f084e560b7f8" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_PercentageOfTaxReceivableAgreement_b996b930-3a5f-4962-936e-938d5b46148d" xlink:href="sum-20220702.xsd#sum_PercentageOfTaxReceivableAgreement"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IncomeTaxesLineItems_25794e50-5611-4d6e-b74b-277678354813" xlink:to="loc_sum_PercentageOfTaxReceivableAgreement_b996b930-3a5f-4962-936e-938d5b46148d" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_201db662-5233-479b-a7a7-aa36ab066e25" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IncomeTaxesLineItems_25794e50-5611-4d6e-b74b-277678354813" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_201db662-5233-479b-a7a7-aa36ab066e25" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_TaxReceivableAgreementLiability_4d7906c0-fa85-4994-947b-1806b40607c4" xlink:href="sum-20220702.xsd#sum_TaxReceivableAgreementLiability"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IncomeTaxesLineItems_25794e50-5611-4d6e-b74b-277678354813" xlink:to="loc_sum_TaxReceivableAgreementLiability_4d7906c0-fa85-4994-947b-1806b40607c4" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedPartnersCapitalAccountDistributionAmount_cdba6e29-0318-49d4-8220-697f743ce097" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LimitedPartnersCapitalAccountDistributionAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_IncomeTaxesLineItems_25794e50-5611-4d6e-b74b-277678354813" xlink:to="loc_us-gaap_LimitedPartnersCapitalAccountDistributionAmount_cdba6e29-0318-49d4-8220-697f743ce097" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_IncomeTaxesTable_494d6026-7c6d-4d03-8e3b-712fd33fd0b4" xlink:href="sum-20220702.xsd#sum_IncomeTaxesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_IncomeTaxesLineItems_25794e50-5611-4d6e-b74b-277678354813" xlink:to="loc_sum_IncomeTaxesTable_494d6026-7c6d-4d03-8e3b-712fd33fd0b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_21701396-2c60-4df3-a7cb-5c8217168ed6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_IncomeTaxesTable_494d6026-7c6d-4d03-8e3b-712fd33fd0b4" xlink:to="loc_us-gaap_StatementClassOfStockAxis_21701396-2c60-4df3-a7cb-5c8217168ed6" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_21701396-2c60-4df3-a7cb-5c8217168ed6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_21701396-2c60-4df3-a7cb-5c8217168ed6" xlink:to="loc_us-gaap_ClassOfStockDomain_21701396-2c60-4df3-a7cb-5c8217168ed6_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_768af6a7-c961-41ee-bdcb-b54219a509bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_21701396-2c60-4df3-a7cb-5c8217168ed6" xlink:to="loc_us-gaap_ClassOfStockDomain_768af6a7-c961-41ee-bdcb-b54219a509bf" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_e9cba2a4-173b-4ddc-8a9d-699f35683b0f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_768af6a7-c961-41ee-bdcb-b54219a509bf" xlink:to="loc_us-gaap_CommonClassAMember_e9cba2a4-173b-4ddc-8a9d-699f35683b0f" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a10dc33d-da68-4e53-b0da-da87e0244657" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_IncomeTaxesTable_494d6026-7c6d-4d03-8e3b-712fd33fd0b4" xlink:to="loc_dei_LegalEntityAxis_a10dc33d-da68-4e53-b0da-da87e0244657" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a10dc33d-da68-4e53-b0da-da87e0244657_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a10dc33d-da68-4e53-b0da-da87e0244657" xlink:to="loc_dei_EntityDomain_a10dc33d-da68-4e53-b0da-da87e0244657_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_8c917f6b-994e-4388-8bac-5e28f7422773" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a10dc33d-da68-4e53-b0da-da87e0244657" xlink:to="loc_dei_EntityDomain_8c917f6b-994e-4388-8bac-5e28f7422773" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitHoldingsLpMember_ba4a70c8-28fc-40b7-a2cb-d74ce7ca7247" xlink:href="sum-20220702.xsd#sum_SummitHoldingsLpMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_8c917f6b-994e-4388-8bac-5e28f7422773" xlink:to="loc_sum_SummitHoldingsLpMember_ba4a70c8-28fc-40b7-a2cb-d74ce7ca7247" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_1d2cd5db-c7a7-42fa-9a16-1810ca8d4d1e" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_8c917f6b-994e-4388-8bac-5e28f7422773" xlink:to="loc_sum_SummitMaterialsLlcMember_1d2cd5db-c7a7-42fa-9a16-1810ca8d4d1e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_9939f0f1-8567-478b-aff6-b1ff3815dc19" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfArrangementAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_IncomeTaxesTable_494d6026-7c6d-4d03-8e3b-712fd33fd0b4" xlink:to="loc_us-gaap_TypeOfArrangementAxis_9939f0f1-8567-478b-aff6-b1ff3815dc19" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_9939f0f1-8567-478b-aff6-b1ff3815dc19_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_9939f0f1-8567-478b-aff6-b1ff3815dc19" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_9939f0f1-8567-478b-aff6-b1ff3815dc19_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_36583b34-3f79-4d95-af9b-e97c8f67839c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_9939f0f1-8567-478b-aff6-b1ff3815dc19" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_36583b34-3f79-4d95-af9b-e97c8f67839c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_TaxReceivableAgreementMember_901c9d5d-9e64-4542-86bb-622faed8718a" xlink:href="sum-20220702.xsd#sum_TaxReceivableAgreementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_36583b34-3f79-4d95-af9b-e97c8f67839c" xlink:to="loc_sum_TaxReceivableAgreementMember_901c9d5d-9e64-4542-86bb-622faed8718a" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/EARNINGSPERSHAREScheduleofBasictoDilutedIncomePerShareDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#EARNINGSPERSHAREScheduleofBasictoDilutedIncomePerShareDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/EARNINGSPERSHAREScheduleofBasictoDilutedIncomePerShareDetails" xlink:type="extended" id="id80b8ed888234b279bd29f43da015fb9_EARNINGSPERSHAREScheduleofBasictoDilutedIncomePerShareDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareBasicLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_da18c17e-dddd-4bd5-8fa1-56e943ba73ce" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_da18c17e-dddd-4bd5-8fa1-56e943ba73ce" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_fbeb7025-7e70-44ab-a66a-766ac930f946" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_fbeb7025-7e70-44ab-a66a-766ac930f946" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesRestrictedStock_143420b4-1292-4fb0-acf3-972589e54f37" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesRestrictedStock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesRestrictedStock_143420b4-1292-4fb0-acf3-972589e54f37" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_79e767cc-d947-4902-9123-9a83f1ef7f5a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_400d15c4-aedf-4673-b581-99d771ba0354" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareBasic"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_EarningsPerShareBasic_400d15c4-aedf-4673-b581-99d771ba0354" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToParentDiluted_ac4e41fe-26c7-4da9-bca5-c94e1a9979a7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLossAttributableToParentDiluted"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_NetIncomeLossAttributableToParentDiluted_ac4e41fe-26c7-4da9-bca5-c94e1a9979a7" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_2aeaeaeb-cf15-455c-9cad-d6de5837e614" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_2aeaeaeb-cf15-455c-9cad-d6de5837e614" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToCallOptionsAndWarrants_4650a192-b7d5-414d-9965-550fdfb4a1f7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncrementalCommonSharesAttributableToCallOptionsAndWarrants"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToCallOptionsAndWarrants_4650a192-b7d5-414d-9965-550fdfb4a1f7" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_d9a87956-c70c-4999-91ef-30c91898eddc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_d9a87956-c70c-4999-91ef-30c91898eddc" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_7cba7fb8-85a8-4e03-9b99-308590f9c851" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareDiluted"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_EarningsPerShareDiluted_7cba7fb8-85a8-4e03-9b99-308590f9c851" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_2b50e24e-bab5-44ae-9e3e-bc8feb8a6500" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_2b50e24e-bab5-44ae-9e3e-bc8feb8a6500" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_8004df5b-8ff9-4d19-b746-a880f6175e0d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_98eb1e8f-dc8e-4f14-afd3-a5fff477f921" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_8004df5b-8ff9-4d19-b746-a880f6175e0d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_6427eaac-8ade-45ea-8d1a-15e0d1acbf59" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_8004df5b-8ff9-4d19-b746-a880f6175e0d" xlink:to="loc_us-gaap_StatementClassOfStockAxis_6427eaac-8ade-45ea-8d1a-15e0d1acbf59" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_6427eaac-8ade-45ea-8d1a-15e0d1acbf59_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6427eaac-8ade-45ea-8d1a-15e0d1acbf59" xlink:to="loc_us-gaap_ClassOfStockDomain_6427eaac-8ade-45ea-8d1a-15e0d1acbf59_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_8e39e239-e883-4f6a-a5ff-72525cf9320b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6427eaac-8ade-45ea-8d1a-15e0d1acbf59" xlink:to="loc_us-gaap_ClassOfStockDomain_8e39e239-e883-4f6a-a5ff-72525cf9320b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CommonClassAAndRestrictedStockMember_d4694a34-d8d5-4409-98f6-3590db4327d4" xlink:href="sum-20220702.xsd#sum_CommonClassAAndRestrictedStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_8e39e239-e883-4f6a-a5ff-72525cf9320b" xlink:to="loc_sum_CommonClassAAndRestrictedStockMember_d4694a34-d8d5-4409-98f6-3590db4327d4" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_ee08a129-9184-45fb-9ea1-6ee6f51bbd3f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_CommonClassAAndRestrictedStockMember_d4694a34-d8d5-4409-98f6-3590db4327d4" xlink:to="loc_us-gaap_CommonClassAMember_ee08a129-9184-45fb-9ea1-6ee6f51bbd3f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_1886d3cc-b4c2-4867-af2e-ec20a034f086" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_CommonClassAAndRestrictedStockMember_d4694a34-d8d5-4409-98f6-3590db4327d4" xlink:to="loc_us-gaap_RestrictedStockMember_1886d3cc-b4c2-4867-af2e-ec20a034f086" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_02fd283b-f9a5-4976-b0ad-0929fb33fbec" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_8004df5b-8ff9-4d19-b746-a880f6175e0d" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_02fd283b-f9a5-4976-b0ad-0929fb33fbec" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_02fd283b-f9a5-4976-b0ad-0929fb33fbec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_02fd283b-f9a5-4976-b0ad-0929fb33fbec" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_02fd283b-f9a5-4976-b0ad-0929fb33fbec_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_a5641a65-d5c2-47f6-ba73-dc0aaa7789b5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_02fd283b-f9a5-4976-b0ad-0929fb33fbec" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_a5641a65-d5c2-47f6-ba73-dc0aaa7789b5" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_5cd50d8b-16e1-494a-92e4-02f7a94e83e2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_a5641a65-d5c2-47f6-ba73-dc0aaa7789b5" xlink:to="loc_us-gaap_EmployeeStockOptionMember_5cd50d8b-16e1-494a-92e4-02f7a94e83e2" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_LimitedPartnershipUnitsMember_8164ccfa-a79b-4105-b3cc-8d0fc254180f" xlink:href="sum-20220702.xsd#sum_LimitedPartnershipUnitsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_a5641a65-d5c2-47f6-ba73-dc0aaa7789b5" xlink:to="loc_sum_LimitedPartnershipUnitsMember_8164ccfa-a79b-4105-b3cc-8d0fc254180f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_12a868a1-e26f-4b98-b57f-cda3a4455e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AwardTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareDilutedByCommonClassTable_8004df5b-8ff9-4d19-b746-a880f6175e0d" xlink:to="loc_us-gaap_AwardTypeAxis_12a868a1-e26f-4b98-b57f-cda3a4455e5d" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_12a868a1-e26f-4b98-b57f-cda3a4455e5d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_12a868a1-e26f-4b98-b57f-cda3a4455e5d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_12a868a1-e26f-4b98-b57f-cda3a4455e5d_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e2db9d9e-7c1c-497f-af62-3d9384295af4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_12a868a1-e26f-4b98-b57f-cda3a4455e5d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e2db9d9e-7c1c-497f-af62-3d9384295af4" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_LimitedPartnershipUnitsMember_e1c8c89e-7617-46de-8415-b7dafc34b1d4" xlink:href="sum-20220702.xsd#sum_LimitedPartnershipUnitsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e2db9d9e-7c1c-497f-af62-3d9384295af4" xlink:to="loc_sum_LimitedPartnershipUnitsMember_e1c8c89e-7617-46de-8415-b7dafc34b1d4" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_cbfeb79a-ead4-4458-9cc9-9da2130d85c6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e2db9d9e-7c1c-497f-af62-3d9384295af4" xlink:to="loc_us-gaap_EmployeeStockOptionMember_cbfeb79a-ead4-4458-9cc9-9da2130d85c6" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_a2f0a0b2-0a48-4b88-a820-c7132b93665d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e2db9d9e-7c1c-497f-af62-3d9384295af4" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_a2f0a0b2-0a48-4b88-a820-c7132b93665d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_202b059d-cd85-4f1b-ab33-500f4e62e800" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PerformanceSharesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e2db9d9e-7c1c-497f-af62-3d9384295af4" xlink:to="loc_us-gaap_PerformanceSharesMember_202b059d-cd85-4f1b-ab33-500f4e62e800" xlink:type="arc" order="3"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/STOCKHOLDERSEQUITYMEMBERSINTEREST" xlink:type="simple" xlink:href="sum-20220702.xsd#STOCKHOLDERSEQUITYMEMBERSINTEREST"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/STOCKHOLDERSEQUITYMEMBERSINTEREST" xlink:type="extended" id="ia717e67f855a4a58adfda81f7a48aa78_STOCKHOLDERSEQUITYMEMBERSINTEREST">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_e25bf2dd-442d-45eb-b96f-0707e4eeece3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCapitalizationEquityLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityNoteDisclosureTextBlock_04e90268-9917-4496-8d7b-25ef250d7657" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityNoteDisclosureTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_e25bf2dd-442d-45eb-b96f-0707e4eeece3" xlink:to="loc_us-gaap_StockholdersEquityNoteDisclosureTextBlock_04e90268-9917-4496-8d7b-25ef250d7657" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_MembersEquityNotesDisclosureTextBlock_fd32d2a6-6fbe-4d7b-93f8-1b5ae8d2ac93" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MembersEquityNotesDisclosureTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_e25bf2dd-442d-45eb-b96f-0707e4eeece3" xlink:to="loc_us-gaap_MembersEquityNotesDisclosureTextBlock_fd32d2a6-6fbe-4d7b-93f8-1b5ae8d2ac93" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCapitalizationEquityTable_a83ffa5d-e70d-4d6a-87f8-8f2ae6f444dd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCapitalizationEquityTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_e25bf2dd-442d-45eb-b96f-0707e4eeece3" xlink:to="loc_us-gaap_ScheduleOfCapitalizationEquityTable_a83ffa5d-e70d-4d6a-87f8-8f2ae6f444dd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_12093489-8dfb-4a4b-ae56-56c8e43db1fb" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityTable_a83ffa5d-e70d-4d6a-87f8-8f2ae6f444dd" xlink:to="loc_dei_LegalEntityAxis_12093489-8dfb-4a4b-ae56-56c8e43db1fb" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_12093489-8dfb-4a4b-ae56-56c8e43db1fb_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_12093489-8dfb-4a4b-ae56-56c8e43db1fb" xlink:to="loc_dei_EntityDomain_12093489-8dfb-4a4b-ae56-56c8e43db1fb_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_ac00afb2-d65c-4adc-ac21-63ae9817b179" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_12093489-8dfb-4a4b-ae56-56c8e43db1fb" xlink:to="loc_dei_EntityDomain_ac00afb2-d65c-4adc-ac21-63ae9817b179" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_81179fcf-1eef-458a-8093-c9f2b34b0b5b" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_ac00afb2-d65c-4adc-ac21-63ae9817b179" xlink:to="loc_sum_SummitMaterialsLlcMember_81179fcf-1eef-458a-8093-c9f2b34b0b5b" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/STOCKHOLDERSEQUITYMEMBERSINTERESTTables" xlink:type="simple" xlink:href="sum-20220702.xsd#STOCKHOLDERSEQUITYMEMBERSINTERESTTables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/STOCKHOLDERSEQUITYMEMBERSINTERESTTables" xlink:type="extended" id="ifcb060af2fb042649ef88028ded7c7f6_STOCKHOLDERSEQUITYMEMBERSINTERESTTables">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_a3b38934-d3da-408a-a5db-33cec33ba8d0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCapitalizationEquityLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTextBlock_73c8d25d-8ddd-466e-a26a-6d272307cb07" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_a3b38934-d3da-408a-a5db-33cec33ba8d0" xlink:to="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTextBlock_73c8d25d-8ddd-466e-a26a-6d272307cb07" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_d78ddae0-43c5-47c3-8e96-86efd8779202" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_a3b38934-d3da-408a-a5db-33cec33ba8d0" xlink:to="loc_us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock_d78ddae0-43c5-47c3-8e96-86efd8779202" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCapitalizationEquityTable_3a03171d-d737-486c-8ebf-787583e38b95" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCapitalizationEquityTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_a3b38934-d3da-408a-a5db-33cec33ba8d0" xlink:to="loc_us-gaap_ScheduleOfCapitalizationEquityTable_3a03171d-d737-486c-8ebf-787583e38b95" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_4ce9c9c3-558f-4fac-9d52-8867858756c2" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityTable_3a03171d-d737-486c-8ebf-787583e38b95" xlink:to="loc_dei_LegalEntityAxis_4ce9c9c3-558f-4fac-9d52-8867858756c2" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_4ce9c9c3-558f-4fac-9d52-8867858756c2_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_4ce9c9c3-558f-4fac-9d52-8867858756c2" xlink:to="loc_dei_EntityDomain_4ce9c9c3-558f-4fac-9d52-8867858756c2_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_48752f98-87c0-4bfa-abe5-aaf6d109bf91" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_4ce9c9c3-558f-4fac-9d52-8867858756c2" xlink:to="loc_dei_EntityDomain_48752f98-87c0-4bfa-abe5-aaf6d109bf91" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_10282fd5-c8e1-4c86-8f72-6e22e2ff4d0b" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_48752f98-87c0-4bfa-abe5-aaf6d109bf91" xlink:to="loc_sum_SummitMaterialsLlcMember_10282fd5-c8e1-4c86-8f72-6e22e2ff4d0b" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/STOCKHOLDERSEQUITYMEMBERSINTERESTNarrativeDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#STOCKHOLDERSEQUITYMEMBERSINTERESTNarrativeDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/STOCKHOLDERSEQUITYMEMBERSINTERESTNarrativeDetails" xlink:type="extended" id="i404e6f326ab840e6add95d4ac05e39a1_STOCKHOLDERSEQUITYMEMBERSINTERESTNarrativeDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_ba3ac851-18a4-4422-8483-a52c2d52c68a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCapitalizationEquityLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_6a05d5f7-027c-44f7-8c01-d3fb74434201" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchaseProgramAuthorizedAmount1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_ba3ac851-18a4-4422-8483-a52c2d52c68a" xlink:to="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_6a05d5f7-027c-44f7-8c01-d3fb74434201" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_fd44b8f0-734a-433c-84ed-03e2f1ea309f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_ba3ac851-18a4-4422-8483-a52c2d52c68a" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_fd44b8f0-734a-433c-84ed-03e2f1ea309f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_569bec74-aef6-4953-ae6e-2a88a403d2cc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_ba3ac851-18a4-4422-8483-a52c2d52c68a" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_569bec74-aef6-4953-ae6e-2a88a403d2cc" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_d372bf05-b90e-404a-afd3-219bfd05b13c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_ba3ac851-18a4-4422-8483-a52c2d52c68a" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_d372bf05-b90e-404a-afd3-219bfd05b13c" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCapitalizationEquityTable_29e18260-49d2-4828-8480-90f550dfdb5a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCapitalizationEquityTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_ba3ac851-18a4-4422-8483-a52c2d52c68a" xlink:to="loc_us-gaap_ScheduleOfCapitalizationEquityTable_29e18260-49d2-4828-8480-90f550dfdb5a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_3125f284-c18a-4c02-9856-7490c17cb74b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityTable_29e18260-49d2-4828-8480-90f550dfdb5a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_3125f284-c18a-4c02-9856-7490c17cb74b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_3125f284-c18a-4c02-9856-7490c17cb74b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_3125f284-c18a-4c02-9856-7490c17cb74b" xlink:to="loc_us-gaap_ClassOfStockDomain_3125f284-c18a-4c02-9856-7490c17cb74b_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_c376a9f0-6bbe-4adb-8372-6597100e3387" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_3125f284-c18a-4c02-9856-7490c17cb74b" xlink:to="loc_us-gaap_ClassOfStockDomain_c376a9f0-6bbe-4adb-8372-6597100e3387" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_2c32e4d1-da0a-4126-b632-f20b6c31affa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_c376a9f0-6bbe-4adb-8372-6597100e3387" xlink:to="loc_us-gaap_CommonClassAMember_2c32e4d1-da0a-4126-b632-f20b6c31affa" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_b2163480-8d31-4a0a-b03c-c2c298734a1f" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_OwnershipAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityTable_29e18260-49d2-4828-8480-90f550dfdb5a" xlink:to="loc_srt_OwnershipAxis_b2163480-8d31-4a0a-b03c-c2c298734a1f" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_b2163480-8d31-4a0a-b03c-c2c298734a1f_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_OwnershipDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_b2163480-8d31-4a0a-b03c-c2c298734a1f" xlink:to="loc_srt_OwnershipDomain_b2163480-8d31-4a0a-b03c-c2c298734a1f_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_80171272-1480-4642-9999-37b9447b8af8" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_OwnershipDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_b2163480-8d31-4a0a-b03c-c2c298734a1f" xlink:to="loc_srt_OwnershipDomain_80171272-1480-4642-9999-37b9447b8af8" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitHoldingsLpMember_8b79f18e-e700-4602-b6a8-2b3c87c327c7" xlink:href="sum-20220702.xsd#sum_SummitHoldingsLpMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_80171272-1480-4642-9999-37b9447b8af8" xlink:to="loc_sum_SummitHoldingsLpMember_8b79f18e-e700-4602-b6a8-2b3c87c327c7" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/STOCKHOLDERSEQUITYMEMBERSINTERESTEquityOfferingsDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#STOCKHOLDERSEQUITYMEMBERSINTERESTEquityOfferingsDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/STOCKHOLDERSEQUITYMEMBERSINTERESTEquityOfferingsDetails" xlink:type="extended" id="ie9f8a663ea254ff1a96d05660cd4c2fd_STOCKHOLDERSEQUITYMEMBERSINTERESTEquityOfferingsDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_77bdebd4-3007-4dee-b5c6-4516047a41af" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCapitalizationEquityLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4164fbe7-540e-4e8a-87ab-94ab26785566" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_77bdebd4-3007-4dee-b5c6-4516047a41af" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4164fbe7-540e-4e8a-87ab-94ab26785566" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_cfc1e0be-72fe-4987-92e3-b3abc2efbd2a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4164fbe7-540e-4e8a-87ab-94ab26785566" xlink:to="loc_us-gaap_CommonStockSharesIssued_cfc1e0be-72fe-4987-92e3-b3abc2efbd2a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_fd205f9f-ccc3-402d-8278-a0b4203dab5a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4164fbe7-540e-4e8a-87ab-94ab26785566" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits_fd205f9f-ccc3-402d-8278-a0b4203dab5a" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_60bd9951-4e59-4289-8c1f-3e7c7325eabf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4164fbe7-540e-4e8a-87ab-94ab26785566" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_60bd9951-4e59-4289-8c1f-3e7c7325eabf" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_2d530ece-b9f8-4abf-bf30-fdb58e2379ec" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4164fbe7-540e-4e8a-87ab-94ab26785566" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_2d530ece-b9f8-4abf-bf30-fdb58e2379ec" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_OtherEquityActivityShares_0643e298-cbf1-4455-8d81-d1ef0766a21a" xlink:href="sum-20220702.xsd#sum_OtherEquityActivityShares"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4164fbe7-540e-4e8a-87ab-94ab26785566" xlink:to="loc_sum_OtherEquityActivityShares_0643e298-cbf1-4455-8d81-d1ef0766a21a" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_69564c95-afd7-4320-ad05-ef95fe493f66" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockSharesIssued"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding_8f851b92-ddfe-4e57-842a-0a29ee1ccf32" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4164fbe7-540e-4e8a-87ab-94ab26785566" xlink:to="loc_us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding_8f851b92-ddfe-4e57-842a-0a29ee1ccf32" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_LimitedPartnersCapitalAccountUnitsExchanged_31ed1bc1-1f16-4233-9428-7d2168bb741f" xlink:href="sum-20220702.xsd#sum_LimitedPartnersCapitalAccountUnitsExchanged"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4164fbe7-540e-4e8a-87ab-94ab26785566" xlink:to="loc_sum_LimitedPartnersCapitalAccountUnitsExchanged_31ed1bc1-1f16-4233-9428-7d2168bb741f" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding_0e87d053-c4d4-46ef-adf7-98719a7a1874" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LimitedPartnersCapitalAccountUnitsOutstanding"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_5cecc36c-bff1-4d1f-ac6e-eaa213fac20b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4164fbe7-540e-4e8a-87ab-94ab26785566" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_5cecc36c-bff1-4d1f-ac6e-eaa213fac20b" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCapitalizationEquityTable_bac75089-e9ae-492d-a3b8-de9fcec663ef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCapitalizationEquityTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityLineItems_77bdebd4-3007-4dee-b5c6-4516047a41af" xlink:to="loc_us-gaap_ScheduleOfCapitalizationEquityTable_bac75089-e9ae-492d-a3b8-de9fcec663ef" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_6887bab8-4bbb-4e3e-b378-efaf941d0782" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_OwnershipAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityTable_bac75089-e9ae-492d-a3b8-de9fcec663ef" xlink:to="loc_srt_OwnershipAxis_6887bab8-4bbb-4e3e-b378-efaf941d0782" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_6887bab8-4bbb-4e3e-b378-efaf941d0782_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_OwnershipDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_6887bab8-4bbb-4e3e-b378-efaf941d0782" xlink:to="loc_srt_OwnershipDomain_6887bab8-4bbb-4e3e-b378-efaf941d0782_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_81aa571c-ee76-4dfe-ad0d-90b174881a17" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_OwnershipDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_6887bab8-4bbb-4e3e-b378-efaf941d0782" xlink:to="loc_srt_OwnershipDomain_81aa571c-ee76-4dfe-ad0d-90b174881a17" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitHoldingsLpMember_c47f9d74-a6ee-43f7-853d-edfaf235844a" xlink:href="sum-20220702.xsd#sum_SummitHoldingsLpMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_81aa571c-ee76-4dfe-ad0d-90b174881a17" xlink:to="loc_sum_SummitHoldingsLpMember_c47f9d74-a6ee-43f7-853d-edfaf235844a" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsIncMember_36595fe7-201a-4ec0-bd7e-77b4ba556cad" xlink:href="sum-20220702.xsd#sum_SummitMaterialsIncMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_81aa571c-ee76-4dfe-ad0d-90b174881a17" xlink:to="loc_sum_SummitMaterialsIncMember_36595fe7-201a-4ec0-bd7e-77b4ba556cad" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalUnitsByClassAxis_d43a6139-362e-46bc-b8dd-a51eeefcf158" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalUnitsByClassAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityTable_bac75089-e9ae-492d-a3b8-de9fcec663ef" xlink:to="loc_us-gaap_CapitalUnitsByClassAxis_d43a6139-362e-46bc-b8dd-a51eeefcf158" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalUnitClassDomain_d43a6139-362e-46bc-b8dd-a51eeefcf158_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalUnitClassDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CapitalUnitsByClassAxis_d43a6139-362e-46bc-b8dd-a51eeefcf158" xlink:to="loc_us-gaap_CapitalUnitClassDomain_d43a6139-362e-46bc-b8dd-a51eeefcf158_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalUnitClassDomain_5ca9f1d3-75d2-4d82-9c0e-10c003d1d437" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalUnitClassDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CapitalUnitsByClassAxis_d43a6139-362e-46bc-b8dd-a51eeefcf158" xlink:to="loc_us-gaap_CapitalUnitClassDomain_5ca9f1d3-75d2-4d82-9c0e-10c003d1d437" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_LpUnitsMember_57707da3-e073-43fc-8e74-0f756662a6ea" xlink:href="sum-20220702.xsd#sum_LpUnitsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalUnitClassDomain_5ca9f1d3-75d2-4d82-9c0e-10c003d1d437" xlink:to="loc_sum_LpUnitsMember_57707da3-e073-43fc-8e74-0f756662a6ea" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_950fc7af-ed8a-4164-b6a5-0a579a7c9f1d" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityTable_bac75089-e9ae-492d-a3b8-de9fcec663ef" xlink:to="loc_dei_LegalEntityAxis_950fc7af-ed8a-4164-b6a5-0a579a7c9f1d" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_950fc7af-ed8a-4164-b6a5-0a579a7c9f1d_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_950fc7af-ed8a-4164-b6a5-0a579a7c9f1d" xlink:to="loc_dei_EntityDomain_950fc7af-ed8a-4164-b6a5-0a579a7c9f1d_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5621a8db-643e-488b-827c-033574f72390" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_950fc7af-ed8a-4164-b6a5-0a579a7c9f1d" xlink:to="loc_dei_EntityDomain_5621a8db-643e-488b-827c-033574f72390" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitHoldingsLpMember_11035156-940f-4d65-8cea-ca9a9192aec4" xlink:href="sum-20220702.xsd#sum_SummitHoldingsLpMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5621a8db-643e-488b-827c-033574f72390" xlink:to="loc_sum_SummitHoldingsLpMember_11035156-940f-4d65-8cea-ca9a9192aec4" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsIncorporatedAndSummitHoldingsLPMember_630d6472-01f8-4ac7-862c-845387473f81" xlink:href="sum-20220702.xsd#sum_SummitMaterialsIncorporatedAndSummitHoldingsLPMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5621a8db-643e-488b-827c-033574f72390" xlink:to="loc_sum_SummitMaterialsIncorporatedAndSummitHoldingsLPMember_630d6472-01f8-4ac7-862c-845387473f81" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_78adc46d-9086-4aa6-858b-76103e45f45f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementClassOfStockAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCapitalizationEquityTable_bac75089-e9ae-492d-a3b8-de9fcec663ef" xlink:to="loc_us-gaap_StatementClassOfStockAxis_78adc46d-9086-4aa6-858b-76103e45f45f" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_78adc46d-9086-4aa6-858b-76103e45f45f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_78adc46d-9086-4aa6-858b-76103e45f45f" xlink:to="loc_us-gaap_ClassOfStockDomain_78adc46d-9086-4aa6-858b-76103e45f45f_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_2672208f-79c4-418b-8dab-49520a871c19" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ClassOfStockDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_78adc46d-9086-4aa6-858b-76103e45f45f" xlink:to="loc_us-gaap_ClassOfStockDomain_2672208f-79c4-418b-8dab-49520a871c19" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_2337a2d8-bc0c-4a24-8c84-a1fe227ea4a1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonClassAMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_2672208f-79c4-418b-8dab-49520a871c19" xlink:to="loc_us-gaap_CommonClassAMember_2337a2d8-bc0c-4a24-8c84-a1fe227ea4a1" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/STOCKHOLDERSEQUITYMEMBERSINTERESTAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#STOCKHOLDERSEQUITYMEMBERSINTERESTAccumulatedOtherComprehensiveIncomeLossDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/STOCKHOLDERSEQUITYMEMBERSINTERESTAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="extended" id="id817d6254d8e4c2d9f122ebf2e27b55d_STOCKHOLDERSEQUITYMEMBERSINTERESTAccumulatedOtherComprehensiveIncomeLossDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_83f67a2f-2bf6-46a1-8000-718d0a05740c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ec26bac3-6f29-4166-8904-05791e35cb0c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_83f67a2f-2bf6-46a1-8000-718d0a05740c" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ec26bac3-6f29-4166-8904-05791e35cb0c" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_7f187341-6fbe-46a9-8299-0bfa2d643502" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ec26bac3-6f29-4166-8904-05791e35cb0c" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_7f187341-6fbe-46a9-8299-0bfa2d643502" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_87fbc128-bcaf-4955-8de2-8583da2e1b03" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ec26bac3-6f29-4166-8904-05791e35cb0c" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_87fbc128-bcaf-4955-8de2-8583da2e1b03" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_aee84fb1-5b56-47f9-9201-e2e500f84d38" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_466698f6-2a05-4429-909d-738f62e057d6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_83f67a2f-2bf6-46a1-8000-718d0a05740c" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_466698f6-2a05-4429-909d-738f62e057d6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_470eaafe-8366-4e66-ab83-f14401f051c3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_466698f6-2a05-4429-909d-738f62e057d6" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_470eaafe-8366-4e66-ab83-f14401f051c3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_470eaafe-8366-4e66-ab83-f14401f051c3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_470eaafe-8366-4e66-ab83-f14401f051c3" xlink:to="loc_us-gaap_EquityComponentDomain_470eaafe-8366-4e66-ab83-f14401f051c3_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_0d37e637-833f-40af-a58e-db0beedc00aa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_470eaafe-8366-4e66-ab83-f14401f051c3" xlink:to="loc_us-gaap_EquityComponentDomain_0d37e637-833f-40af-a58e-db0beedc00aa" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_934b67ed-dc67-4c7f-9b93-8704996cafb5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0d37e637-833f-40af-a58e-db0beedc00aa" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_934b67ed-dc67-4c7f-9b93-8704996cafb5" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_a9cfe0bb-ffe0-4092-b78b-d63e5c6bbcc0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0d37e637-833f-40af-a58e-db0beedc00aa" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_a9cfe0bb-ffe0-4092-b78b-d63e5c6bbcc0" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_91af4593-3a90-4af2-9254-9440e181c814" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0d37e637-833f-40af-a58e-db0beedc00aa" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_91af4593-3a90-4af2-9254-9440e181c814" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_22ca0f49-2185-400a-ae84-8bece8bced99" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_466698f6-2a05-4429-909d-738f62e057d6" xlink:to="loc_dei_LegalEntityAxis_22ca0f49-2185-400a-ae84-8bece8bced99" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_22ca0f49-2185-400a-ae84-8bece8bced99_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_22ca0f49-2185-400a-ae84-8bece8bced99" xlink:to="loc_dei_EntityDomain_22ca0f49-2185-400a-ae84-8bece8bced99_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_934aa2ee-df1d-4e9b-9550-4de48e4021fa" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_22ca0f49-2185-400a-ae84-8bece8bced99" xlink:to="loc_dei_EntityDomain_934aa2ee-df1d-4e9b-9550-4de48e4021fa" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_ff818f01-7dff-4a42-b6a0-da89e272012f" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_934aa2ee-df1d-4e9b-9550-4de48e4021fa" xlink:to="loc_sum_SummitMaterialsLlcMember_ff818f01-7dff-4a42-b6a0-da89e272012f" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SUPPLEMENTALCASHFLOWINFORMATION" xlink:type="simple" xlink:href="sum-20220702.xsd#SUPPLEMENTALCASHFLOWINFORMATION"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SUPPLEMENTALCASHFLOWINFORMATION" xlink:type="extended" id="i4dc66e7e5d644172990743d280ada7c7_SUPPLEMENTALCASHFLOWINFORMATION">
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfCashFlowSupplementalLineItems_a79345cb-e166-46c8-9e13-d7c72fb5e2c4" xlink:href="sum-20220702.xsd#sum_ScheduleOfCashFlowSupplementalLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowSupplementalDisclosuresTextBlock_e5e9407d-94ae-4681-8627-65d57d82397e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashFlowSupplementalDisclosuresTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfCashFlowSupplementalLineItems_a79345cb-e166-46c8-9e13-d7c72fb5e2c4" xlink:to="loc_us-gaap_CashFlowSupplementalDisclosuresTextBlock_e5e9407d-94ae-4681-8627-65d57d82397e" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfCashFlowSupplementalTable_6123fcbb-fa14-4e0c-8cd1-fecc087cde34" xlink:href="sum-20220702.xsd#sum_ScheduleOfCashFlowSupplementalTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_ScheduleOfCashFlowSupplementalLineItems_a79345cb-e166-46c8-9e13-d7c72fb5e2c4" xlink:to="loc_sum_ScheduleOfCashFlowSupplementalTable_6123fcbb-fa14-4e0c-8cd1-fecc087cde34" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_5253a966-2d47-44f6-9130-a32c259c320b" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_ScheduleOfCashFlowSupplementalTable_6123fcbb-fa14-4e0c-8cd1-fecc087cde34" xlink:to="loc_dei_LegalEntityAxis_5253a966-2d47-44f6-9130-a32c259c320b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5253a966-2d47-44f6-9130-a32c259c320b_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_5253a966-2d47-44f6-9130-a32c259c320b" xlink:to="loc_dei_EntityDomain_5253a966-2d47-44f6-9130-a32c259c320b_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f3e3d734-2367-4075-80de-85b49cbd9a55" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_5253a966-2d47-44f6-9130-a32c259c320b" xlink:to="loc_dei_EntityDomain_f3e3d734-2367-4075-80de-85b49cbd9a55" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_aa18a723-15b0-4511-978d-0405de744d36" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_f3e3d734-2367-4075-80de-85b49cbd9a55" xlink:to="loc_sum_SummitMaterialsLlcMember_aa18a723-15b0-4511-978d-0405de744d36" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SUPPLEMENTALCASHFLOWINFORMATIONTables" xlink:type="simple" xlink:href="sum-20220702.xsd#SUPPLEMENTALCASHFLOWINFORMATIONTables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SUPPLEMENTALCASHFLOWINFORMATIONTables" xlink:type="extended" id="i91477fa85430463ba23b9256235819b9_SUPPLEMENTALCASHFLOWINFORMATIONTables">
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfCashFlowSupplementalLineItems_79da088b-0ee7-4867-a2c3-96fd66e139af" xlink:href="sum-20220702.xsd#sum_ScheduleOfCashFlowSupplementalLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCashFlowSupplementalDisclosuresTableTextBlock_4a43bab8-02a9-45b2-ac4e-9aa3dfa8e248" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfCashFlowSupplementalDisclosuresTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfCashFlowSupplementalLineItems_79da088b-0ee7-4867-a2c3-96fd66e139af" xlink:to="loc_us-gaap_ScheduleOfCashFlowSupplementalDisclosuresTableTextBlock_4a43bab8-02a9-45b2-ac4e-9aa3dfa8e248" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfCashFlowSupplementalTable_bc0a17c5-3b27-4d2a-8363-6a66fc2162d2" xlink:href="sum-20220702.xsd#sum_ScheduleOfCashFlowSupplementalTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_ScheduleOfCashFlowSupplementalLineItems_79da088b-0ee7-4867-a2c3-96fd66e139af" xlink:to="loc_sum_ScheduleOfCashFlowSupplementalTable_bc0a17c5-3b27-4d2a-8363-6a66fc2162d2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_9eeb942f-1c63-43d1-84a8-3e7c53593541" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_ScheduleOfCashFlowSupplementalTable_bc0a17c5-3b27-4d2a-8363-6a66fc2162d2" xlink:to="loc_dei_LegalEntityAxis_9eeb942f-1c63-43d1-84a8-3e7c53593541" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_9eeb942f-1c63-43d1-84a8-3e7c53593541_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_9eeb942f-1c63-43d1-84a8-3e7c53593541" xlink:to="loc_dei_EntityDomain_9eeb942f-1c63-43d1-84a8-3e7c53593541_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_18c8b6e5-4a36-4083-aa77-86cb30e4c5b5" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_9eeb942f-1c63-43d1-84a8-3e7c53593541" xlink:to="loc_dei_EntityDomain_18c8b6e5-4a36-4083-aa77-86cb30e4c5b5" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_6e76c7a3-f064-487e-9e7f-711a936e60cf" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_18c8b6e5-4a36-4083-aa77-86cb30e4c5b5" xlink:to="loc_sum_SummitMaterialsLlcMember_6e76c7a3-f064-487e-9e7f-711a936e60cf" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SUPPLEMENTALCASHFLOWINFORMATIONScheduleofSupplementalCashFlowInformationDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#SUPPLEMENTALCASHFLOWINFORMATIONScheduleofSupplementalCashFlowInformationDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SUPPLEMENTALCASHFLOWINFORMATIONScheduleofSupplementalCashFlowInformationDetails" xlink:type="extended" id="ib187e0ae0f6a4bb9807e05cd2e6f9eaa_SUPPLEMENTALCASHFLOWINFORMATIONScheduleofSupplementalCashFlowInformationDetails">
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfCashFlowSupplementalLineItems_563307e3-a028-4b6d-9bc7-7c7c50fe34e3" xlink:href="sum-20220702.xsd#sum_ScheduleOfCashFlowSupplementalLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_30ff62c9-d30b-419c-aebb-2ba3d4a25ffd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfCashFlowSupplementalLineItems_563307e3-a028-4b6d-9bc7-7c7c50fe34e3" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_30ff62c9-d30b-419c-aebb-2ba3d4a25ffd" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_0c90188d-fa2b-44d8-8b20-a9d9ca4430b8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestPaidNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_30ff62c9-d30b-419c-aebb-2ba3d4a25ffd" xlink:to="loc_us-gaap_InterestPaidNet_0c90188d-fa2b-44d8-8b20-a9d9ca4430b8" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_dfebeae4-aea7-42f9-8be3-796d6ead420b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxesPaidNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_30ff62c9-d30b-419c-aebb-2ba3d4a25ffd" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_dfebeae4-aea7-42f9-8be3-796d6ead420b" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeasePayments_bbd41c93-c788-45a1-ad8f-ba7faf008ffe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeasePayments"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_30ff62c9-d30b-419c-aebb-2ba3d4a25ffd" xlink:to="loc_us-gaap_OperatingLeasePayments_bbd41c93-c788-45a1-ad8f-ba7faf008ffe" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseInterestPaymentOnLiability_9323f69c-7d41-40d6-af8b-e687bb1fb76c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseInterestPaymentOnLiability"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_30ff62c9-d30b-419c-aebb-2ba3d4a25ffd" xlink:to="loc_us-gaap_FinanceLeaseInterestPaymentOnLiability_9323f69c-7d41-40d6-af8b-e687bb1fb76c" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeasePrincipalPayments_21d94e5a-73de-4fb1-9d38-2c10c7bc7e89" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeasePrincipalPayments"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_30ff62c9-d30b-419c-aebb-2ba3d4a25ffd" xlink:to="loc_us-gaap_FinanceLeasePrincipalPayments_21d94e5a-73de-4fb1-9d38-2c10c7bc7e89" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_NonCashFinancingActivitiesAbstract_b1aac2b0-80c3-46b6-9624-89a6f4bb88b3" xlink:href="sum-20220702.xsd#sum_NonCashFinancingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_ScheduleOfCashFlowSupplementalLineItems_563307e3-a028-4b6d-9bc7-7c7c50fe34e3" xlink:to="loc_sum_NonCashFinancingActivitiesAbstract_b1aac2b0-80c3-46b6-9624-89a6f4bb88b3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_32b3fe01-f036-4d9a-b71a-a59f9648c7ef" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_NonCashFinancingActivitiesAbstract_b1aac2b0-80c3-46b6-9624-89a6f4bb88b3" xlink:to="loc_us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_32b3fe01-f036-4d9a-b71a-a59f9648c7ef" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability_4177d45f-9bc1-4c28-984a-cb4945c12258" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_NonCashFinancingActivitiesAbstract_b1aac2b0-80c3-46b6-9624-89a6f4bb88b3" xlink:to="loc_us-gaap_RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability_4177d45f-9bc1-4c28-984a-cb4945c12258" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockAmountConverted1_a14a1a3a-3b03-4bb6-a9d4-88f5bd9a208d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConversionOfStockAmountConverted1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_NonCashFinancingActivitiesAbstract_b1aac2b0-80c3-46b6-9624-89a6f4bb88b3" xlink:to="loc_us-gaap_ConversionOfStockAmountConverted1_a14a1a3a-3b03-4bb6-a9d4-88f5bd9a208d" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ScheduleOfCashFlowSupplementalTable_2ffacccf-acae-4f18-ba3c-aa4b099c091c" xlink:href="sum-20220702.xsd#sum_ScheduleOfCashFlowSupplementalTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_sum_ScheduleOfCashFlowSupplementalLineItems_563307e3-a028-4b6d-9bc7-7c7c50fe34e3" xlink:to="loc_sum_ScheduleOfCashFlowSupplementalTable_2ffacccf-acae-4f18-ba3c-aa4b099c091c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a0cdac5c-6fbf-4938-9939-c72fb6925c93" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_sum_ScheduleOfCashFlowSupplementalTable_2ffacccf-acae-4f18-ba3c-aa4b099c091c" xlink:to="loc_dei_LegalEntityAxis_a0cdac5c-6fbf-4938-9939-c72fb6925c93" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a0cdac5c-6fbf-4938-9939-c72fb6925c93_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a0cdac5c-6fbf-4938-9939-c72fb6925c93" xlink:to="loc_dei_EntityDomain_a0cdac5c-6fbf-4938-9939-c72fb6925c93_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_99b10f0b-44b3-4333-a6af-7335f3ec4e07" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a0cdac5c-6fbf-4938-9939-c72fb6925c93" xlink:to="loc_dei_EntityDomain_99b10f0b-44b3-4333-a6af-7335f3ec4e07" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_7aabbb34-8a27-443e-801f-74d2bc0adde4" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_99b10f0b-44b3-4333-a6af-7335f3ec4e07" xlink:to="loc_sum_SummitMaterialsLlcMember_7aabbb34-8a27-443e-801f-74d2bc0adde4" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/LEASES" xlink:type="simple" xlink:href="sum-20220702.xsd#LEASES"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/LEASES" xlink:type="extended" id="i18a7da6b83b843b49eaabf36dae6085c_LEASES">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_711a4b95-a483-493a-8b62-dae32a4d4afc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeasesTextBlock_9a9b2dd8-34d4-4aa0-b19c-461faaf92a67" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeasesTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_711a4b95-a483-493a-8b62-dae32a4d4afc" xlink:to="loc_us-gaap_LesseeOperatingLeasesTextBlock_9a9b2dd8-34d4-4aa0-b19c-461faaf92a67" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeFinanceLeasesTextBlock_d2356680-2ad2-4dcb-8792-82fd9c6b05d8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeFinanceLeasesTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_711a4b95-a483-493a-8b62-dae32a4d4afc" xlink:to="loc_us-gaap_LesseeFinanceLeasesTextBlock_d2356680-2ad2-4dcb-8792-82fd9c6b05d8" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_34c5863d-b7eb-431f-9dba-3f63d81c49cd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_711a4b95-a483-493a-8b62-dae32a4d4afc" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_34c5863d-b7eb-431f-9dba-3f63d81c49cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_0a679f2d-0052-48aa-83e6-4156c9953a4e" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_34c5863d-b7eb-431f-9dba-3f63d81c49cd" xlink:to="loc_dei_LegalEntityAxis_0a679f2d-0052-48aa-83e6-4156c9953a4e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0a679f2d-0052-48aa-83e6-4156c9953a4e_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_0a679f2d-0052-48aa-83e6-4156c9953a4e" xlink:to="loc_dei_EntityDomain_0a679f2d-0052-48aa-83e6-4156c9953a4e_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_063493bc-6124-4a40-b867-ab0f380ba2d1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_0a679f2d-0052-48aa-83e6-4156c9953a4e" xlink:to="loc_dei_EntityDomain_063493bc-6124-4a40-b867-ab0f380ba2d1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_4fdd4cea-6be4-4ba6-aebc-6ea5f10b7474" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_063493bc-6124-4a40-b867-ab0f380ba2d1" xlink:to="loc_sum_SummitMaterialsLlcMember_4fdd4cea-6be4-4ba6-aebc-6ea5f10b7474" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/LEASESTables" xlink:type="simple" xlink:href="sum-20220702.xsd#LEASESTables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/LEASESTables" xlink:type="extended" id="id905a0570bd1490e95f013aeafd943df_LEASESTables">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_943590f3-bfc2-4e17-a5bb-24f88706768a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseCostTableTextBlock_7d5f9199-d0f5-4b67-b904-dd9b7b4b9f20" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseCostTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_943590f3-bfc2-4e17-a5bb-24f88706768a" xlink:to="loc_us-gaap_LeaseCostTableTextBlock_7d5f9199-d0f5-4b67-b904-dd9b7b4b9f20" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AssetsAndLiabilitiesLesseeTableTextBlock_5f3d7555-65a9-4e37-bb11-9edff6320d27" xlink:href="sum-20220702.xsd#sum_AssetsAndLiabilitiesLesseeTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_943590f3-bfc2-4e17-a5bb-24f88706768a" xlink:to="loc_sum_AssetsAndLiabilitiesLesseeTableTextBlock_5f3d7555-65a9-4e37-bb11-9edff6320d27" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityMaturityTableTextBlock_52414f20-3eb1-4ad8-b404-3407aed5e410" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityMaturityTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_943590f3-bfc2-4e17-a5bb-24f88706768a" xlink:to="loc_us-gaap_FinanceLeaseLiabilityMaturityTableTextBlock_52414f20-3eb1-4ad8-b404-3407aed5e410" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_544299c3-59b3-475b-8578-58a9a9c092cd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_943590f3-bfc2-4e17-a5bb-24f88706768a" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_544299c3-59b3-475b-8578-58a9a9c092cd" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_00be0745-c8d2-4a9e-a06a-9e0adfe399bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_943590f3-bfc2-4e17-a5bb-24f88706768a" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_00be0745-c8d2-4a9e-a06a-9e0adfe399bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_5fa09497-c70a-4702-bee6-c1c71c2fc294" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_00be0745-c8d2-4a9e-a06a-9e0adfe399bf" xlink:to="loc_dei_LegalEntityAxis_5fa09497-c70a-4702-bee6-c1c71c2fc294" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5fa09497-c70a-4702-bee6-c1c71c2fc294_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_5fa09497-c70a-4702-bee6-c1c71c2fc294" xlink:to="loc_dei_EntityDomain_5fa09497-c70a-4702-bee6-c1c71c2fc294_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_7d9dbca7-de2c-4dea-9ccc-c41f92b4ff8c" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_5fa09497-c70a-4702-bee6-c1c71c2fc294" xlink:to="loc_dei_EntityDomain_7d9dbca7-de2c-4dea-9ccc-c41f92b4ff8c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_2f54ab9b-a59a-4d9d-b9c3-1230c40ee057" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7d9dbca7-de2c-4dea-9ccc-c41f92b4ff8c" xlink:to="loc_sum_SummitMaterialsLlcMember_2f54ab9b-a59a-4d9d-b9c3-1230c40ee057" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/LEASESOperatingandFinanceLeasesDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#LEASESOperatingandFinanceLeasesDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/LEASESOperatingandFinanceLeasesDetails" xlink:type="extended" id="i718e9923f163430d8ad599c7a30a79e8_LEASESOperatingandFinanceLeasesDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_bdcfc070-e393-40b4-a2bd-5f493618d44c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseCostAbstract_e5bf716b-507d-4da5-8eb4-2fc5432eb65b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseCostAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_bdcfc070-e393-40b4-a2bd-5f493618d44c" xlink:to="loc_us-gaap_LeaseCostAbstract_e5bf716b-507d-4da5-8eb4-2fc5432eb65b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseCost_cb91a7f7-e73a-41dd-b8f0-03cf0846afbe" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseCost"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseCostAbstract_e5bf716b-507d-4da5-8eb4-2fc5432eb65b" xlink:to="loc_us-gaap_OperatingLeaseCost_cb91a7f7-e73a-41dd-b8f0-03cf0846afbe" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableLeaseCost_3cd1b510-71a7-425e-98c5-d5a57c855c01" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableLeaseCost"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseCostAbstract_e5bf716b-507d-4da5-8eb4-2fc5432eb65b" xlink:to="loc_us-gaap_VariableLeaseCost_3cd1b510-71a7-425e-98c5-d5a57c855c01" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermLeaseCost_86503758-6315-4f61-b750-326d8cf38707" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShortTermLeaseCost"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseCostAbstract_e5bf716b-507d-4da5-8eb4-2fc5432eb65b" xlink:to="loc_us-gaap_ShortTermLeaseCost_86503758-6315-4f61-b750-326d8cf38707" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_FinanceLeaseCost1Abstract_5e3ce234-2069-4965-8036-8be38ec8444c" xlink:href="sum-20220702.xsd#sum_FinanceLeaseCost1Abstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseCostAbstract_e5bf716b-507d-4da5-8eb4-2fc5432eb65b" xlink:to="loc_sum_FinanceLeaseCost1Abstract_5e3ce234-2069-4965-8036-8be38ec8444c" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseRightOfUseAssetAmortization_943bb705-2193-419a-a121-6d1243fc0284" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseRightOfUseAssetAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_FinanceLeaseCost1Abstract_5e3ce234-2069-4965-8036-8be38ec8444c" xlink:to="loc_us-gaap_FinanceLeaseRightOfUseAssetAmortization_943bb705-2193-419a-a121-6d1243fc0284" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseInterestExpense_690f2496-0dc4-47ea-a6f0-a5dec52d9840" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseInterestExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_FinanceLeaseCost1Abstract_5e3ce234-2069-4965-8036-8be38ec8444c" xlink:to="loc_us-gaap_FinanceLeaseInterestExpense_690f2496-0dc4-47ea-a6f0-a5dec52d9840" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseCost_a8752b35-c6f8-4640-bc22-89aa784b69ca" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseCost"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseCostAbstract_e5bf716b-507d-4da5-8eb4-2fc5432eb65b" xlink:to="loc_us-gaap_LeaseCost_a8752b35-c6f8-4640-bc22-89aa784b69ca" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAndLiabilitiesLesseeAbstract_870f80c6-5ca2-4713-8d32-f85b8698c782" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAndLiabilitiesLesseeAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_bdcfc070-e393-40b4-a2bd-5f493618d44c" xlink:to="loc_us-gaap_AssetsAndLiabilitiesLesseeAbstract_870f80c6-5ca2-4713-8d32-f85b8698c782" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_OperatingLeasesAbstract_3943aefc-4b85-4738-832c-93e780a80818" xlink:href="sum-20220702.xsd#sum_OperatingLeasesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAndLiabilitiesLesseeAbstract_870f80c6-5ca2-4713-8d32-f85b8698c782" xlink:to="loc_sum_OperatingLeasesAbstract_3943aefc-4b85-4738-832c-93e780a80818" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_1ac5db65-f272-4f18-9d61-4b0b0a95800a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_OperatingLeasesAbstract_3943aefc-4b85-4738-832c-93e780a80818" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_1ac5db65-f272-4f18-9d61-4b0b0a95800a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_bebda8c5-57d7-4446-9ed9-34880cfc2fe2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_OperatingLeasesAbstract_3943aefc-4b85-4738-832c-93e780a80818" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_bebda8c5-57d7-4446-9ed9-34880cfc2fe2" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_996983c1-05e2-4772-9bac-75224d485073" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_OperatingLeasesAbstract_3943aefc-4b85-4738-832c-93e780a80818" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_996983c1-05e2-4772-9bac-75224d485073" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiability_62aeffe0-bd7e-4ee2-b564-e26f72931d4a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiability"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_OperatingLeasesAbstract_3943aefc-4b85-4738-832c-93e780a80818" xlink:to="loc_us-gaap_OperatingLeaseLiability_62aeffe0-bd7e-4ee2-b564-e26f72931d4a" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_FinanceLeasesAbstract_a2649386-98fb-45e4-a75c-4ba3a6eea618" xlink:href="sum-20220702.xsd#sum_FinanceLeasesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAndLiabilitiesLesseeAbstract_870f80c6-5ca2-4713-8d32-f85b8698c782" xlink:to="loc_sum_FinanceLeasesAbstract_a2649386-98fb-45e4-a75c-4ba3a6eea618" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization_17690acc-0d9d-47cb-934e-dae47dd3ddb2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_FinanceLeasesAbstract_a2649386-98fb-45e4-a75c-4ba3a6eea618" xlink:to="loc_us-gaap_FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization_17690acc-0d9d-47cb-934e-dae47dd3ddb2" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseRightOfUseAssetAccumulatedAmortization_b7fbc282-fa4f-48a8-b8df-30972d5dfbec" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseRightOfUseAssetAccumulatedAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_FinanceLeasesAbstract_a2649386-98fb-45e4-a75c-4ba3a6eea618" xlink:to="loc_us-gaap_FinanceLeaseRightOfUseAssetAccumulatedAmortization_b7fbc282-fa4f-48a8-b8df-30972d5dfbec" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList_e10b0c42-7065-4fe6-919a-5923c8bb9f60" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_FinanceLeasesAbstract_a2649386-98fb-45e4-a75c-4ba3a6eea618" xlink:to="loc_us-gaap_FinanceLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList_e10b0c42-7065-4fe6-919a-5923c8bb9f60" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseRightOfUseAsset_ce729677-5ea5-487b-9f57-83dd50d926b2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseRightOfUseAsset"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_FinanceLeasesAbstract_a2649386-98fb-45e4-a75c-4ba3a6eea618" xlink:to="loc_us-gaap_FinanceLeaseRightOfUseAsset_ce729677-5ea5-487b-9f57-83dd50d926b2" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityCurrent_73360da7-f179-4bd6-bd59-5c11fc66c69b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_FinanceLeasesAbstract_a2649386-98fb-45e4-a75c-4ba3a6eea618" xlink:to="loc_us-gaap_FinanceLeaseLiabilityCurrent_73360da7-f179-4bd6-bd59-5c11fc66c69b" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityNoncurrent_cb542fb7-ad7e-4070-8292-e109180765ab" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_FinanceLeasesAbstract_a2649386-98fb-45e4-a75c-4ba3a6eea618" xlink:to="loc_us-gaap_FinanceLeaseLiabilityNoncurrent_cb542fb7-ad7e-4070-8292-e109180765ab" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiability_b7f145df-188c-4a74-ac0c-af9c26c6270c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiability"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_FinanceLeasesAbstract_a2649386-98fb-45e4-a75c-4ba3a6eea618" xlink:to="loc_us-gaap_FinanceLeaseLiability_b7f145df-188c-4a74-ac0c-af9c26c6270c" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_WeightedAverageLeaseTermAndDiscountRateAbstract_53f54c18-aaa2-43ae-8998-10a76fdf91f2" xlink:href="sum-20220702.xsd#sum_WeightedAverageLeaseTermAndDiscountRateAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_bdcfc070-e393-40b4-a2bd-5f493618d44c" xlink:to="loc_sum_WeightedAverageLeaseTermAndDiscountRateAbstract_53f54c18-aaa2-43ae-8998-10a76fdf91f2" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_d46e805f-7031-4f0c-9e9c-d3e607619d27" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_WeightedAverageLeaseTermAndDiscountRateAbstract_53f54c18-aaa2-43ae-8998-10a76fdf91f2" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_d46e805f-7031-4f0c-9e9c-d3e607619d27" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseWeightedAverageRemainingLeaseTerm1_57a20249-acf1-4cde-be4b-530745b3381f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseWeightedAverageRemainingLeaseTerm1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_WeightedAverageLeaseTermAndDiscountRateAbstract_53f54c18-aaa2-43ae-8998-10a76fdf91f2" xlink:to="loc_us-gaap_FinanceLeaseWeightedAverageRemainingLeaseTerm1_57a20249-acf1-4cde-be4b-530745b3381f" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_LeaseDiscountRateAbstract_97506471-7671-4c6b-9f26-2e70b08ca8c7" xlink:href="sum-20220702.xsd#sum_LeaseDiscountRateAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_bdcfc070-e393-40b4-a2bd-5f493618d44c" xlink:to="loc_sum_LeaseDiscountRateAbstract_97506471-7671-4c6b-9f26-2e70b08ca8c7" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_5b693762-8c1d-42f6-8770-66586d748e91" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_LeaseDiscountRateAbstract_97506471-7671-4c6b-9f26-2e70b08ca8c7" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_5b693762-8c1d-42f6-8770-66586d748e91" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseWeightedAverageDiscountRatePercent_020fa021-14de-430e-b4d0-82f8a2986d4c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseWeightedAverageDiscountRatePercent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sum_LeaseDiscountRateAbstract_97506471-7671-4c6b-9f26-2e70b08ca8c7" xlink:to="loc_us-gaap_FinanceLeaseWeightedAverageDiscountRatePercent_020fa021-14de-430e-b4d0-82f8a2986d4c" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_bdcfc070-e393-40b4-a2bd-5f493618d44c" xlink:to="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear_8e02d5bd-71bb-41db-9ab6-4459a7aa25bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsRemainderOfFiscalYear_8e02d5bd-71bb-41db-9ab6-4459a7aa25bf" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_155ed93a-4dce-4187-830f-41258eee0d33" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_155ed93a-4dce-4187-830f-41258eee0d33" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_83cc6fde-296d-49e9-a425-fe4af2c54f34" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_83cc6fde-296d-49e9-a425-fe4af2c54f34" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_fe0b8c7d-f68d-4b7d-a905-ab808684a2f4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_fe0b8c7d-f68d-4b7d-a905-ab808684a2f4" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_68e91503-c46a-4d4c-9a8f-9e26da97fa42" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_68e91503-c46a-4d4c-9a8f-9e26da97fa42" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_1081d8cb-31e8-4bb0-a327-8c8bac4a63fa" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_1081d8cb-31e8-4bb0-a327-8c8bac4a63fa" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive_e0538585-01f3-436a-95bc-ae442a326247" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive_e0538585-01f3-436a-95bc-ae442a326247" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_97f81c79-2488-4c69-ab5c-fb4e3fca4a98" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_97f81c79-2488-4c69-ab5c-fb4e3fca4a98" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_cfa17a4b-738e-4322-810f-5163fa86e2ce" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeaseLiabilitiesPaymentsDueAbstract_08f2d538-f111-40dc-8a14-bbbbc52b0e4e" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_cfa17a4b-738e-4322-810f-5163fa86e2ce" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiability_b8b66f8a-bde4-4b7e-9205-df5dfed2cc7f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiability"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_bdcfc070-e393-40b4-a2bd-5f493618d44c" xlink:to="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityPaymentsRemainderOfFiscalYear_fe951969-7ded-4b71-99dd-f24cfaa45f82" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityPaymentsRemainderOfFiscalYear"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:to="loc_us-gaap_FinanceLeaseLiabilityPaymentsRemainderOfFiscalYear_fe951969-7ded-4b71-99dd-f24cfaa45f82" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueNextTwelveMonths_fa053dea-b4d5-4816-b45c-1d7627af5f77" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityPaymentsDueNextTwelveMonths"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:to="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueNextTwelveMonths_fa053dea-b4d5-4816-b45c-1d7627af5f77" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueYearTwo_53045868-431f-43b0-b4ae-7e79039cce04" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityPaymentsDueYearTwo"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:to="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueYearTwo_53045868-431f-43b0-b4ae-7e79039cce04" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueYearThree_c718f0bf-9385-4b4d-abdd-509d20aabfa0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityPaymentsDueYearThree"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:to="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueYearThree_c718f0bf-9385-4b4d-abdd-509d20aabfa0" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueYearFour_ee51a0f0-219c-4347-a3a4-189e132db5eb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityPaymentsDueYearFour"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:to="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueYearFour_ee51a0f0-219c-4347-a3a4-189e132db5eb" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueYearFive_72f95e39-b783-47ce-97ea-7c1d249b1775" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityPaymentsDueYearFive"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:to="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueYearFive_72f95e39-b783-47ce-97ea-7c1d249b1775" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueAfterYearFive_512e7556-92f5-4957-b559-55686fa05c89" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityPaymentsDueAfterYearFive"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:to="loc_us-gaap_FinanceLeaseLiabilityPaymentsDueAfterYearFive_512e7556-92f5-4957-b559-55686fa05c89" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityPaymentsDue_6d201bde-1e7c-4140-ab0f-68c014e35747" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityPaymentsDue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:to="loc_us-gaap_FinanceLeaseLiabilityPaymentsDue_6d201bde-1e7c-4140-ab0f-68c014e35747" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiabilityUndiscountedExcessAmount_ea39587c-55a0-431b-b3e3-c12af2e68215" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiabilityUndiscountedExcessAmount"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract_2b8b1269-2337-450d-bd4c-5241a09f1c32" xlink:to="loc_us-gaap_FinanceLeaseLiabilityUndiscountedExcessAmount_ea39587c-55a0-431b-b3e3-c12af2e68215" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseLiability_8f2e6393-a7c4-41bd-90c4-caea1cacef92" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinanceLeaseLiability"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_cd4accf5-6615-412f-84bd-58c213695291" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_bdcfc070-e393-40b4-a2bd-5f493618d44c" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_cd4accf5-6615-412f-84bd-58c213695291" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_0ac99741-8bdf-4e15-a5d1-482eccefbe24" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_cd4accf5-6615-412f-84bd-58c213695291" xlink:to="loc_dei_LegalEntityAxis_0ac99741-8bdf-4e15-a5d1-482eccefbe24" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0ac99741-8bdf-4e15-a5d1-482eccefbe24_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_0ac99741-8bdf-4e15-a5d1-482eccefbe24" xlink:to="loc_dei_EntityDomain_0ac99741-8bdf-4e15-a5d1-482eccefbe24_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_d658f610-bc6a-4e3d-8b3c-b59485b980dc" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_0ac99741-8bdf-4e15-a5d1-482eccefbe24" xlink:to="loc_dei_EntityDomain_d658f610-bc6a-4e3d-8b3c-b59485b980dc" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_4a2fc439-366e-47ae-ba09-774cd691d4c9" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_d658f610-bc6a-4e3d-8b3c-b59485b980dc" xlink:to="loc_sum_SummitMaterialsLlcMember_4a2fc439-366e-47ae-ba09-774cd691d4c9" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/COMMITMENTSANDCONTINGENCIES" xlink:type="simple" xlink:href="sum-20220702.xsd#COMMITMENTSANDCONTINGENCIES"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/COMMITMENTSANDCONTINGENCIES" xlink:type="extended" id="i6b35f98ded384c22bd3901b3d1bcfd3f_COMMITMENTSANDCONTINGENCIES">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_5607e3ba-3727-45b4-bec1-8fcd265c4594" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_1bf14c45-f84d-476a-ab80-430d9547586b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommitmentsAndContingenciesDisclosureTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_5607e3ba-3727-45b4-bec1-8fcd265c4594" xlink:to="loc_us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_1bf14c45-f84d-476a-ab80-430d9547586b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_8abc8d47-c009-452c-8bd2-d6cf4cd84896" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_5607e3ba-3727-45b4-bec1-8fcd265c4594" xlink:to="loc_us-gaap_LossContingenciesTable_8abc8d47-c009-452c-8bd2-d6cf4cd84896" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_e4f6d867-c21a-488b-9c05-e7d8ec2cb568" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_8abc8d47-c009-452c-8bd2-d6cf4cd84896" xlink:to="loc_dei_LegalEntityAxis_e4f6d867-c21a-488b-9c05-e7d8ec2cb568" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e4f6d867-c21a-488b-9c05-e7d8ec2cb568_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_e4f6d867-c21a-488b-9c05-e7d8ec2cb568" xlink:to="loc_dei_EntityDomain_e4f6d867-c21a-488b-9c05-e7d8ec2cb568_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_8ff728ee-dc67-4615-8ef2-c983905ba7ac" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_e4f6d867-c21a-488b-9c05-e7d8ec2cb568" xlink:to="loc_dei_EntityDomain_8ff728ee-dc67-4615-8ef2-c983905ba7ac" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_006e5378-7d81-49cf-bfd4-eeb2758dc8a5" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_8ff728ee-dc67-4615-8ef2-c983905ba7ac" xlink:to="loc_sum_SummitMaterialsLlcMember_006e5378-7d81-49cf-bfd4-eeb2758dc8a5" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#COMMITMENTSANDCONTINGENCIESNarrativeDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/COMMITMENTSANDCONTINGENCIESNarrativeDetails" xlink:type="extended" id="i8f83ba2e419a4d9b9147d5d3eaabf9f4_COMMITMENTSANDCONTINGENCIESNarrativeDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_1512864a-07d9-4edb-8bed-1358cec53d82" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetRetirementObligationsNoncurrent_855f8649-eb8e-47ba-a3e4-f01fd1b43e11" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetRetirementObligationsNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_1512864a-07d9-4edb-8bed-1358cec53d82" xlink:to="loc_us-gaap_AssetRetirementObligationsNoncurrent_855f8649-eb8e-47ba-a3e4-f01fd1b43e11" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetRetirementObligationCurrent_5a63a32c-53f6-4397-a2c2-5e1ba58590c5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetRetirementObligationCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_1512864a-07d9-4edb-8bed-1358cec53d82" xlink:to="loc_us-gaap_AssetRetirementObligationCurrent_5a63a32c-53f6-4397-a2c2-5e1ba58590c5" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AssetRetirementObligationExpectedCost_190a1434-415a-4fdf-9526-e609f24accd6" xlink:href="sum-20220702.xsd#sum_AssetRetirementObligationExpectedCost"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_1512864a-07d9-4edb-8bed-1358cec53d82" xlink:to="loc_sum_AssetRetirementObligationExpectedCost_190a1434-415a-4fdf-9526-e609f24accd6" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_PurchaseCommitmentTerms_ee7a5471-e845-4d3d-ad14-ed439a2980da" xlink:href="sum-20220702.xsd#sum_PurchaseCommitmentTerms"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_1512864a-07d9-4edb-8bed-1358cec53d82" xlink:to="loc_sum_PurchaseCommitmentTerms_ee7a5471-e845-4d3d-ad14-ed439a2980da" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_ad51d6aa-0d9e-4d9e-ac55-69502b4a6245" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_1512864a-07d9-4edb-8bed-1358cec53d82" xlink:to="loc_us-gaap_LossContingenciesTable_ad51d6aa-0d9e-4d9e-ac55-69502b4a6245" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_071cbf98-cf7b-451f-9feb-2fa049d6da1a" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_ad51d6aa-0d9e-4d9e-ac55-69502b4a6245" xlink:to="loc_dei_LegalEntityAxis_071cbf98-cf7b-451f-9feb-2fa049d6da1a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_071cbf98-cf7b-451f-9feb-2fa049d6da1a_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_071cbf98-cf7b-451f-9feb-2fa049d6da1a" xlink:to="loc_dei_EntityDomain_071cbf98-cf7b-451f-9feb-2fa049d6da1a_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_4478d238-c860-4673-a010-e18e8658e573" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_071cbf98-cf7b-451f-9feb-2fa049d6da1a" xlink:to="loc_dei_EntityDomain_4478d238-c860-4673-a010-e18e8658e573" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_0470e7f4-c572-46a4-804e-8332d9899083" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_4478d238-c860-4673-a010-e18e8658e573" xlink:to="loc_sum_SummitMaterialsLlcMember_0470e7f4-c572-46a4-804e-8332d9899083" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_797ca9c2-d274-4d32-82a4-38c54a4efc0f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_ad51d6aa-0d9e-4d9e-ac55-69502b4a6245" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_797ca9c2-d274-4d32-82a4-38c54a4efc0f" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_797ca9c2-d274-4d32-82a4-38c54a4efc0f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyNatureDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_797ca9c2-d274-4d32-82a4-38c54a4efc0f" xlink:to="loc_us-gaap_LossContingencyNatureDomain_797ca9c2-d274-4d32-82a4-38c54a4efc0f_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_76d2bd97-2650-489f-8541-cfad3c692107" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyNatureDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_797ca9c2-d274-4d32-82a4-38c54a4efc0f" xlink:to="loc_us-gaap_LossContingencyNatureDomain_76d2bd97-2650-489f-8541-cfad3c692107" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SiteRestorationObligationsMember_33e8fdf0-0bcc-435d-88c2-4889a05fb383" xlink:href="sum-20220702.xsd#sum_SiteRestorationObligationsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_76d2bd97-2650-489f-8541-cfad3c692107" xlink:to="loc_sum_SiteRestorationObligationsMember_33e8fdf0-0bcc-435d-88c2-4889a05fb383" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_4e0c9d6d-a720-4914-9a28-10aa30a0242f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_ad51d6aa-0d9e-4d9e-ac55-69502b4a6245" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_4e0c9d6d-a720-4914-9a28-10aa30a0242f" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_4e0c9d6d-a720-4914-9a28-10aa30a0242f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_4e0c9d6d-a720-4914-9a28-10aa30a0242f" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_4e0c9d6d-a720-4914-9a28-10aa30a0242f_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_aeffbfaf-65d2-4f1b-b2a3-186db046238c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_4e0c9d6d-a720-4914-9a28-10aa30a0242f" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_aeffbfaf-65d2-4f1b-b2a3-186db046238c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncurrentLiabilitiesMember_c623cec4-b518-41fd-811a-dde932bb4685" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherNoncurrentLiabilitiesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_aeffbfaf-65d2-4f1b-b2a3-186db046238c" xlink:to="loc_us-gaap_OtherNoncurrentLiabilitiesMember_c623cec4-b518-41fd-811a-dde932bb4685" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesMember_790e4a57-3409-4987-bb38-cc337a7e1ac9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_aeffbfaf-65d2-4f1b-b2a3-186db046238c" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesMember_790e4a57-3409-4987-bb38-cc337a7e1ac9" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/FAIRVALUE" xlink:type="simple" xlink:href="sum-20220702.xsd#FAIRVALUE"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/FAIRVALUE" xlink:type="extended" id="i69c2232c74b44486b626547a533952ce_FAIRVALUE">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2507facb-f0fe-40b5-af5b-39ebde1ae7ee" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosuresTextBlock_6845e595-bf5b-44e4-a5a9-34a5d0991aaf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueDisclosuresTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2507facb-f0fe-40b5-af5b-39ebde1ae7ee" xlink:to="loc_us-gaap_FairValueDisclosuresTextBlock_6845e595-bf5b-44e4-a5a9-34a5d0991aaf" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_48dae3fa-f701-4002-b3a3-a54c08ead3a5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2507facb-f0fe-40b5-af5b-39ebde1ae7ee" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_48dae3fa-f701-4002-b3a3-a54c08ead3a5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a5e1da90-a9ec-45a8-8def-135242a56ad3" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_48dae3fa-f701-4002-b3a3-a54c08ead3a5" xlink:to="loc_dei_LegalEntityAxis_a5e1da90-a9ec-45a8-8def-135242a56ad3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a5e1da90-a9ec-45a8-8def-135242a56ad3_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a5e1da90-a9ec-45a8-8def-135242a56ad3" xlink:to="loc_dei_EntityDomain_a5e1da90-a9ec-45a8-8def-135242a56ad3_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_13498b35-e93d-4e15-b40a-02e25b352af1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a5e1da90-a9ec-45a8-8def-135242a56ad3" xlink:to="loc_dei_EntityDomain_13498b35-e93d-4e15-b40a-02e25b352af1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_e9c208b3-853b-4d39-985a-2facbd659d0e" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_13498b35-e93d-4e15-b40a-02e25b352af1" xlink:to="loc_sum_SummitMaterialsLlcMember_e9c208b3-853b-4d39-985a-2facbd659d0e" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/FAIRVALUETables" xlink:type="simple" xlink:href="sum-20220702.xsd#FAIRVALUETables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/FAIRVALUETables" xlink:type="extended" id="i68f7cac99e3749ebabd01068066f5a32_FAIRVALUETables">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a520bbb3-0108-4096-8123-1cb144608e81" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTableTextBlock_943b4658-bbc7-4001-9663-52f96b5a6664" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a520bbb3-0108-4096-8123-1cb144608e81" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTableTextBlock_943b4658-bbc7-4001-9663-52f96b5a6664" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTextBlock_ee17bc2a-688f-4e11-b14f-2790d0ce5183" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByBalanceSheetGroupingTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a520bbb3-0108-4096-8123-1cb144608e81" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTextBlock_ee17bc2a-688f-4e11-b14f-2790d0ce5183" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_27a7e2a1-9576-4e90-903d-855cd5d9be6d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a520bbb3-0108-4096-8123-1cb144608e81" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_27a7e2a1-9576-4e90-903d-855cd5d9be6d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_5e5be3b2-fd3c-44e4-947a-32e60b9174b0" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_27a7e2a1-9576-4e90-903d-855cd5d9be6d" xlink:to="loc_dei_LegalEntityAxis_5e5be3b2-fd3c-44e4-947a-32e60b9174b0" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5e5be3b2-fd3c-44e4-947a-32e60b9174b0_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_5e5be3b2-fd3c-44e4-947a-32e60b9174b0" xlink:to="loc_dei_EntityDomain_5e5be3b2-fd3c-44e4-947a-32e60b9174b0_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_8c140a11-d5e1-4fc6-a5af-c233f31a5510" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_5e5be3b2-fd3c-44e4-947a-32e60b9174b0" xlink:to="loc_dei_EntityDomain_8c140a11-d5e1-4fc6-a5af-c233f31a5510" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_bb335111-a1fb-46f8-a033-d8f1ade2b66f" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_8c140a11-d5e1-4fc6-a5af-c233f31a5510" xlink:to="loc_sum_SummitMaterialsLlcMember_bb335111-a1fb-46f8-a033-d8f1ade2b66f" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/FAIRVALUEFairValueMeasurementsDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#FAIRVALUEFairValueMeasurementsDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/FAIRVALUEFairValueMeasurementsDetails" xlink:type="extended" id="if93e0aeb9a8a4166974440369617dd9b_FAIRVALUEFairValueMeasurementsDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_dfa92a90-9383-4903-ade4-1cfdf78af1fd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent_45a63fc4-2001-4cb8-9e1c-1df4bd42cbf0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_dfa92a90-9383-4903-ade4-1cfdf78af1fd" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityCurrent_45a63fc4-2001-4cb8-9e1c-1df4bd42cbf0" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_06634804-cd1a-4be6-bd4b-bd59e1111d68" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_dfa92a90-9383-4903-ade4-1cfdf78af1fd" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent_06634804-cd1a-4be6-bd4b-bd59e1111d68" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_2d40d101-9a89-4a70-99f8-311c64be952e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_dfa92a90-9383-4903-ade4-1cfdf78af1fd" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_2d40d101-9a89-4a70-99f8-311c64be952e" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_0f946fda-3b32-4012-a06e-e05cdda14cca" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_dfa92a90-9383-4903-ade4-1cfdf78af1fd" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_0f946fda-3b32-4012-a06e-e05cdda14cca" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_106efc64-471f-4646-ad8b-56733a63c978" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_dfa92a90-9383-4903-ade4-1cfdf78af1fd" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_106efc64-471f-4646-ad8b-56733a63c978" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_e1483c25-ea99-49a0-b58e-370ab84886f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_106efc64-471f-4646-ad8b-56733a63c978" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_e1483c25-ea99-49a0-b58e-370ab84886f3" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_e1483c25-ea99-49a0-b58e-370ab84886f3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_e1483c25-ea99-49a0-b58e-370ab84886f3" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_e1483c25-ea99-49a0-b58e-370ab84886f3_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_2340b69d-8147-4e8c-96e8-74513592d299" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputTypeDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_e1483c25-ea99-49a0-b58e-370ab84886f3" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_2340b69d-8147-4e8c-96e8-74513592d299" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_b6943e0a-e180-4bcc-8c71-0385f81f8ffd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_2340b69d-8147-4e8c-96e8-74513592d299" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_b6943e0a-e180-4bcc-8c71-0385f81f8ffd" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_9e696f98-ba99-41a6-bef9-d2e831800626" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_106efc64-471f-4646-ad8b-56733a63c978" xlink:to="loc_dei_LegalEntityAxis_9e696f98-ba99-41a6-bef9-d2e831800626" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_9e696f98-ba99-41a6-bef9-d2e831800626_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_9e696f98-ba99-41a6-bef9-d2e831800626" xlink:to="loc_dei_EntityDomain_9e696f98-ba99-41a6-bef9-d2e831800626_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_6f5d1a56-51e0-4819-ae92-0154c2369bf9" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_9e696f98-ba99-41a6-bef9-d2e831800626" xlink:to="loc_dei_EntityDomain_6f5d1a56-51e0-4819-ae92-0154c2369bf9" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_1628aa5f-449c-452d-a2b2-70702a3af6d5" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_6f5d1a56-51e0-4819-ae92-0154c2369bf9" xlink:to="loc_sum_SummitMaterialsLlcMember_1628aa5f-449c-452d-a2b2-70702a3af6d5" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_6beeaf5f-4fbf-491c-9f17-fbfc66f7fa05" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_106efc64-471f-4646-ad8b-56733a63c978" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_6beeaf5f-4fbf-491c-9f17-fbfc66f7fa05" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6beeaf5f-4fbf-491c-9f17-fbfc66f7fa05_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_6beeaf5f-4fbf-491c-9f17-fbfc66f7fa05" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6beeaf5f-4fbf-491c-9f17-fbfc66f7fa05_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9afb555e-06a6-432a-a1cd-8e735ca2cf40" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_6beeaf5f-4fbf-491c-9f17-fbfc66f7fa05" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9afb555e-06a6-432a-a1cd-8e735ca2cf40" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_749b58bb-0ef3-454d-a5f2-addf8bfa0daf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9afb555e-06a6-432a-a1cd-8e735ca2cf40" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_749b58bb-0ef3-454d-a5f2-addf8bfa0daf" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/FAIRVALUECarryingValueandFairValueofFinancialInstrumentsDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#FAIRVALUECarryingValueandFairValueofFinancialInstrumentsDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/FAIRVALUECarryingValueandFairValueofFinancialInstrumentsDetails" xlink:type="extended" id="ia99250449a5e4faa98615eccbc1f70b4_FAIRVALUECarryingValueandFairValueofFinancialInstrumentsDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_35061285-d062-4aa9-a633-3694547cc747" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_8fec1b1f-5882-4514-9645-19062ac8cae6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtFairValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_35061285-d062-4aa9-a633-3694547cc747" xlink:to="loc_us-gaap_LongTermDebtFairValue_8fec1b1f-5882-4514-9645-19062ac8cae6" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_DeferredConsiderationAndNoncompeteObligationsCurrentFairValueDisclosure_9b9a1205-e849-4180-9661-e23b7fec8b39" xlink:href="sum-20220702.xsd#sum_DeferredConsiderationAndNoncompeteObligationsCurrentFairValueDisclosure"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_35061285-d062-4aa9-a633-3694547cc747" xlink:to="loc_sum_DeferredConsiderationAndNoncompeteObligationsCurrentFairValueDisclosure_9b9a1205-e849-4180-9661-e23b7fec8b39" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_DeferredConsiderationAndNoncompeteObligationsNoncurrentFairValueDisclosure_2fff5146-217b-4fc5-a127-4e3378a89270" xlink:href="sum-20220702.xsd#sum_DeferredConsiderationAndNoncompeteObligationsNoncurrentFairValueDisclosure"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_35061285-d062-4aa9-a633-3694547cc747" xlink:to="loc_sum_DeferredConsiderationAndNoncompeteObligationsNoncurrentFairValueDisclosure_2fff5146-217b-4fc5-a127-4e3378a89270" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_f5ba7d25-70af-4931-8f27-65e560a66396" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_35061285-d062-4aa9-a633-3694547cc747" xlink:to="loc_us-gaap_LongTermDebtCurrent_f5ba7d25-70af-4931-8f27-65e560a66396" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_a6cd83d1-5f0e-4d00-9a58-b14f6af6c80c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_35061285-d062-4aa9-a633-3694547cc747" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_a6cd83d1-5f0e-4d00-9a58-b14f6af6c80c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_df3ba2cc-7b28-4141-ab33-630e5a74a14b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_a6cd83d1-5f0e-4d00-9a58-b14f6af6c80c" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_df3ba2cc-7b28-4141-ab33-630e5a74a14b" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_df3ba2cc-7b28-4141-ab33-630e5a74a14b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_df3ba2cc-7b28-4141-ab33-630e5a74a14b" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_df3ba2cc-7b28-4141-ab33-630e5a74a14b_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0608acf3-8b6d-435a-a425-117f60c58796" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_df3ba2cc-7b28-4141-ab33-630e5a74a14b" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0608acf3-8b6d-435a-a425-117f60c58796" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_6bab36e0-2dc6-4ba5-a2ae-712535c2865e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel2Member"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0608acf3-8b6d-435a-a425-117f60c58796" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_6bab36e0-2dc6-4ba5-a2ae-712535c2865e" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_1a2e45f9-a068-481e-af3a-929c283ab2ff" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0608acf3-8b6d-435a-a425-117f60c58796" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_1a2e45f9-a068-481e-af3a-929c283ab2ff" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_05f8de9e-0e37-4bc4-a977-19f9c0469792" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_a6cd83d1-5f0e-4d00-9a58-b14f6af6c80c" xlink:to="loc_dei_LegalEntityAxis_05f8de9e-0e37-4bc4-a977-19f9c0469792" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_05f8de9e-0e37-4bc4-a977-19f9c0469792_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_05f8de9e-0e37-4bc4-a977-19f9c0469792" xlink:to="loc_dei_EntityDomain_05f8de9e-0e37-4bc4-a977-19f9c0469792_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_89768d4e-dd77-444e-b5ad-9dabc9ae2809" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_05f8de9e-0e37-4bc4-a977-19f9c0469792" xlink:to="loc_dei_EntityDomain_89768d4e-dd77-444e-b5ad-9dabc9ae2809" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_0a98a63e-221e-4ac3-9bb0-b7a638154f3c" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_89768d4e-dd77-444e-b5ad-9dabc9ae2809" xlink:to="loc_sum_SummitMaterialsLlcMember_0a98a63e-221e-4ac3-9bb0-b7a638154f3c" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_7d0e11bb-f24e-4883-b807-296a8967364d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_a6cd83d1-5f0e-4d00-9a58-b14f6af6c80c" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_7d0e11bb-f24e-4883-b807-296a8967364d" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_7d0e11bb-f24e-4883-b807-296a8967364d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_7d0e11bb-f24e-4883-b807-296a8967364d" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_7d0e11bb-f24e-4883-b807-296a8967364d_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_6aa88551-8729-4bf7-b77d-c0c1fe20a658" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_7d0e11bb-f24e-4883-b807-296a8967364d" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_6aa88551-8729-4bf7-b77d-c0c1fe20a658" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_1babd728-5b9b-4f3f-b8af-b1de4a2b66f9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_6aa88551-8729-4bf7-b77d-c0c1fe20a658" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_1babd728-5b9b-4f3f-b8af-b1de4a2b66f9" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_a1f19569-cf75-46a6-ad3d-bf46ee7f0e11" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_1babd728-5b9b-4f3f-b8af-b1de4a2b66f9" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_a1f19569-cf75-46a6-ad3d-bf46ee7f0e11" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_3d29772c-99f0-4769-b4a9-777134911f7c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_1babd728-5b9b-4f3f-b8af-b1de4a2b66f9" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_3d29772c-99f0-4769-b4a9-777134911f7c" xlink:type="arc" order="2"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SEGMENTINFORMATION" xlink:type="simple" xlink:href="sum-20220702.xsd#SEGMENTINFORMATION"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SEGMENTINFORMATION" xlink:type="extended" id="i761004ad446a478b9bb1e4b0761dbc74_SEGMENTINFORMATION">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_f877c273-fa7c-46bf-8358-1f0dbffb9115" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingInformationLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingDisclosureTextBlock_41307385-633c-4802-b278-4a7857c0f609" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingDisclosureTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_f877c273-fa7c-46bf-8358-1f0dbffb9115" xlink:to="loc_us-gaap_SegmentReportingDisclosureTextBlock_41307385-633c-4802-b278-4a7857c0f609" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_dd435964-7945-4548-9742-c5b4461ee45e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_f877c273-fa7c-46bf-8358-1f0dbffb9115" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_dd435964-7945-4548-9742-c5b4461ee45e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_4175e54c-07e8-40e5-836d-86593f40419f" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_dd435964-7945-4548-9742-c5b4461ee45e" xlink:to="loc_dei_LegalEntityAxis_4175e54c-07e8-40e5-836d-86593f40419f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_4175e54c-07e8-40e5-836d-86593f40419f_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_4175e54c-07e8-40e5-836d-86593f40419f" xlink:to="loc_dei_EntityDomain_4175e54c-07e8-40e5-836d-86593f40419f_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_b4f0d1e4-9b58-4d35-b3ed-9c950a14daaf" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_4175e54c-07e8-40e5-836d-86593f40419f" xlink:to="loc_dei_EntityDomain_b4f0d1e4-9b58-4d35-b3ed-9c950a14daaf" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_92458ac0-fac7-4443-9d3d-bc56f680e537" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_b4f0d1e4-9b58-4d35-b3ed-9c950a14daaf" xlink:to="loc_sum_SummitMaterialsLlcMember_92458ac0-fac7-4443-9d3d-bc56f680e537" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SEGMENTINFORMATIONTables" xlink:type="simple" xlink:href="sum-20220702.xsd#SEGMENTINFORMATIONTables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SEGMENTINFORMATIONTables" xlink:type="extended" id="i8b1a353364ef4b0e882a77e3db29ebb4_SEGMENTINFORMATIONTables">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_9b73a20b-21b4-44c4-90be-cb6f1a920ae6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingInformationLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_a10481e3-31c6-496f-a9e2-a6bd8e49f4af" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_9b73a20b-21b4-44c4-90be-cb6f1a920ae6" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock_a10481e3-31c6-496f-a9e2-a6bd8e49f4af" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_c04b905a-44d7-4460-8826-ec73f0070631" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_9b73a20b-21b4-44c4-90be-cb6f1a920ae6" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_c04b905a-44d7-4460-8826-ec73f0070631" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_60c3efa2-680f-441a-aa9a-abf76b4b9c7f" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_c04b905a-44d7-4460-8826-ec73f0070631" xlink:to="loc_dei_LegalEntityAxis_60c3efa2-680f-441a-aa9a-abf76b4b9c7f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_60c3efa2-680f-441a-aa9a-abf76b4b9c7f_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_60c3efa2-680f-441a-aa9a-abf76b4b9c7f" xlink:to="loc_dei_EntityDomain_60c3efa2-680f-441a-aa9a-abf76b4b9c7f_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_86c9b005-7acd-4210-91cd-6a2822c07119" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_60c3efa2-680f-441a-aa9a-abf76b4b9c7f" xlink:to="loc_dei_EntityDomain_86c9b005-7acd-4210-91cd-6a2822c07119" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_a5792f3c-d08c-4c48-b958-51e73af92c2d" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_86c9b005-7acd-4210-91cd-6a2822c07119" xlink:to="loc_sum_SummitMaterialsLlcMember_a5792f3c-d08c-4c48-b958-51e73af92c2d" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/SEGMENTINFORMATIONFinancialDataDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#SEGMENTINFORMATIONFinancialDataDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/SEGMENTINFORMATIONFinancialDataDetails" xlink:type="extended" id="i5ab4ab9fa1df4d9382af7f6e383571de_SEGMENTINFORMATIONFinancialDataDetails">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentReportingInformationLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_1ab9d5e1-df8a-47ef-8e1f-783dd10fb3b4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfOperatingSegments"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_NumberOfOperatingSegments_1ab9d5e1-df8a-47ef-8e1f-783dd10fb3b4" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_66728e2e-6b49-43ff-b531-abf6b6bbdcfd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NumberOfReportableSegments"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_NumberOfReportableSegments_66728e2e-6b49-43ff-b531-abf6b6bbdcfd" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_340cc72a-eadb-407d-9e33-92f02ce0d07f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_340cc72a-eadb-407d-9e33-92f02ce0d07f" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_3a3bab73-7a21-4eed-a767-87320d03664f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_3a3bab73-7a21-4eed-a767-87320d03664f" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_bde71f3d-e876-4bc6-82fd-aeeb622e0cee" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_InterestExpense_bde71f3d-e876-4bc6-82fd-aeeb622e0cee" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_3d0d0ef0-a4d9-454d-856a-98d7cb6d3414" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_3d0d0ef0-a4d9-454d-856a-98d7cb6d3414" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetRetirementObligationAccretionExpense_5804c1ad-7bb4-46a8-8ec8-1442084bac8e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetRetirementObligationAccretionExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_AssetRetirementObligationAccretionExpense_5804c1ad-7bb4-46a8-8ec8-1442084bac8e" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_TaxReceivableAgreementExpense_efd6ab56-d447-470b-bd19-2e5622912819" xlink:href="sum-20220702.xsd#sum_TaxReceivableAgreementExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_sum_TaxReceivableAgreementExpense_efd6ab56-d447-470b-bd19-2e5622912819" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_e1441efc-f1d9-41f9-b1ed-21ba2c3cc730" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_e1441efc-f1d9-41f9-b1ed-21ba2c3cc730" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_NonCashCompensationExpense_42b6cfea-ef67-449c-be19-8630c88c237f" xlink:href="sum-20220702.xsd#sum_NonCashCompensationExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_sum_NonCashCompensationExpense_42b6cfea-ef67-449c-be19-8630c88c237f" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_MiscellaneousOtherIncomeExpense_dbb2fed8-cda7-4ce7-80c1-0fe058cf8922" xlink:href="sum-20220702.xsd#sum_MiscellaneousOtherIncomeExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_sum_MiscellaneousOtherIncomeExpense_dbb2fed8-cda7-4ce7-80c1-0fe058cf8922" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AdjustedEarningsBeforeInterestIncomeTaxesDepreciationAndAmortization_aaf47cc3-5625-47ce-88ba-3947eb898655" xlink:href="sum-20220702.xsd#sum_AdjustedEarningsBeforeInterestIncomeTaxesDepreciationAndAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_sum_AdjustedEarningsBeforeInterestIncomeTaxesDepreciationAndAmortization_aaf47cc3-5625-47ce-88ba-3947eb898655" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_51c8288d-7a13-41aa-874f-9c013b216a70" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_51c8288d-7a13-41aa-874f-9c013b216a70" xlink:type="arc" order="12"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_DepreciationDepletionAmortizationAndAccretion_c3af75bb-109b-4f1c-a796-4cb472bdca18" xlink:href="sum-20220702.xsd#sum_DepreciationDepletionAmortizationAndAccretion"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_sum_DepreciationDepletionAmortizationAndAccretion_c3af75bb-109b-4f1c-a796-4cb472bdca18" xlink:type="arc" order="13"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_83455c2c-3278-4376-b8e7-53c8646670e8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_Assets_83455c2c-3278-4376-b8e7-53c8646670e8" xlink:type="arc" order="14"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_779b0805-8cb3-4efd-9acf-bb36265f0da3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_2e03d3af-57eb-4672-a929-b863655815ff" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_779b0805-8cb3-4efd-9acf-bb36265f0da3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_027e08b8-e26d-4726-beb0-9744829c2088" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_779b0805-8cb3-4efd-9acf-bb36265f0da3" xlink:to="loc_dei_LegalEntityAxis_027e08b8-e26d-4726-beb0-9744829c2088" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_027e08b8-e26d-4726-beb0-9744829c2088_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_027e08b8-e26d-4726-beb0-9744829c2088" xlink:to="loc_dei_EntityDomain_027e08b8-e26d-4726-beb0-9744829c2088_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_236b186c-54cb-43a7-8be5-d37ca68e1607" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_027e08b8-e26d-4726-beb0-9744829c2088" xlink:to="loc_dei_EntityDomain_236b186c-54cb-43a7-8be5-d37ca68e1607" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_657ad8b5-6b2b-4f05-8b46-32b73b2239c2" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_236b186c-54cb-43a7-8be5-d37ca68e1607" xlink:to="loc_sum_SummitMaterialsLlcMember_657ad8b5-6b2b-4f05-8b46-32b73b2239c2" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_493ce2e5-37ae-4253-a599-393cb8e8ce20" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_779b0805-8cb3-4efd-9acf-bb36265f0da3" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_493ce2e5-37ae-4253-a599-393cb8e8ce20" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_493ce2e5-37ae-4253-a599-393cb8e8ce20_default" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_493ce2e5-37ae-4253-a599-393cb8e8ce20" xlink:to="loc_us-gaap_SegmentDomain_493ce2e5-37ae-4253-a599-393cb8e8ce20_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_cad48d23-f271-4ee7-8def-bb3be0e739b6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SegmentDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_493ce2e5-37ae-4253-a599-393cb8e8ce20" xlink:to="loc_us-gaap_SegmentDomain_cad48d23-f271-4ee7-8def-bb3be0e739b6" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_WestMember_c01774fd-2cf0-4a6a-953a-28cf15d86983" xlink:href="sum-20220702.xsd#sum_WestMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_cad48d23-f271-4ee7-8def-bb3be0e739b6" xlink:to="loc_sum_WestMember_c01774fd-2cf0-4a6a-953a-28cf15d86983" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_EastMember_5913cf23-353f-4b71-8468-4609582e3407" xlink:href="sum-20220702.xsd#sum_EastMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_cad48d23-f271-4ee7-8def-bb3be0e739b6" xlink:to="loc_sum_EastMember_5913cf23-353f-4b71-8468-4609582e3407" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_CementMember_a3345a00-866f-4a1f-8974-291d9b5aa12d" xlink:href="sum-20220702.xsd#sum_CementMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_cad48d23-f271-4ee7-8def-bb3be0e739b6" xlink:to="loc_sum_CementMember_a3345a00-866f-4a1f-8974-291d9b5aa12d" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_8d5ea2f3-b0c7-4bdb-b759-a64947afd430" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_779b0805-8cb3-4efd-9acf-bb36265f0da3" xlink:to="loc_srt_ConsolidationItemsAxis_8d5ea2f3-b0c7-4bdb-b759-a64947afd430" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_8d5ea2f3-b0c7-4bdb-b759-a64947afd430_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_8d5ea2f3-b0c7-4bdb-b759-a64947afd430" xlink:to="loc_srt_ConsolidationItemsDomain_8d5ea2f3-b0c7-4bdb-b759-a64947afd430_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_3da5a927-bb4d-49bd-aded-7f51f8df7caa" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_8d5ea2f3-b0c7-4bdb-b759-a64947afd430" xlink:to="loc_srt_ConsolidationItemsDomain_3da5a927-bb4d-49bd-aded-7f51f8df7caa" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_672b42cd-0c72-4a71-8c1f-8095ee36b030" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingSegmentsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_3da5a927-bb4d-49bd-aded-7f51f8df7caa" xlink:to="loc_us-gaap_OperatingSegmentsMember_672b42cd-0c72-4a71-8c1f-8095ee36b030" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_03e6417d-6ae6-444c-9aaa-653d5e044d00" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateNonSegmentMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_3da5a927-bb4d-49bd-aded-7f51f8df7caa" xlink:to="loc_us-gaap_CorporateNonSegmentMember_03e6417d-6ae6-444c-9aaa-653d5e044d00" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/GUARANTORANDNONGUARANTORFINANCIALINFORMATION" xlink:type="simple" xlink:href="sum-20220702.xsd#GUARANTORANDNONGUARANTORFINANCIALINFORMATION"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/GUARANTORANDNONGUARANTORFINANCIALINFORMATION" xlink:type="extended" id="i1eedc6f544e149dd82d44f2a40ba908b_GUARANTORANDNONGUARANTORFINANCIALINFORMATION">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_daf6865d-252b-41a4-ac78-15c7b3b9e193" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_CondensedFinancialStatementsTextBlock_15d48aa0-5dac-4bad-9a57-0fb22cb89d03" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CondensedFinancialStatementsTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_daf6865d-252b-41a4-ac78-15c7b3b9e193" xlink:to="loc_srt_CondensedFinancialStatementsTextBlock_15d48aa0-5dac-4bad-9a57-0fb22cb89d03" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_8f22074b-4e43-4dc8-936f-87845c78e713" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_daf6865d-252b-41a4-ac78-15c7b3b9e193" xlink:to="loc_us-gaap_StatementTable_8f22074b-4e43-4dc8-936f-87845c78e713" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_75d8d03d-70f7-460f-ba12-8f84437e3613" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8f22074b-4e43-4dc8-936f-87845c78e713" xlink:to="loc_dei_LegalEntityAxis_75d8d03d-70f7-460f-ba12-8f84437e3613" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_75d8d03d-70f7-460f-ba12-8f84437e3613_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_75d8d03d-70f7-460f-ba12-8f84437e3613" xlink:to="loc_dei_EntityDomain_75d8d03d-70f7-460f-ba12-8f84437e3613_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_7f1cd0ed-a0fb-4d63-b7b5-effaa314d978" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_75d8d03d-70f7-460f-ba12-8f84437e3613" xlink:to="loc_dei_EntityDomain_7f1cd0ed-a0fb-4d63-b7b5-effaa314d978" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_d475ef29-d50d-4fa2-ad13-d59185741303" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7f1cd0ed-a0fb-4d63-b7b5-effaa314d978" xlink:to="loc_sum_SummitMaterialsLlcMember_d475ef29-d50d-4fa2-ad13-d59185741303" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/GUARANTORANDNONGUARANTORFINANCIALINFORMATIONTables" xlink:type="simple" xlink:href="sum-20220702.xsd#GUARANTORANDNONGUARANTORFINANCIALINFORMATIONTables"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/GUARANTORANDNONGUARANTORFINANCIALINFORMATIONTables" xlink:type="extended" id="icfbcdfe54d31405ba6c149a7acc1f4dd_GUARANTORANDNONGUARANTORFINANCIALINFORMATIONTables">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_3e19ce96-2305-45c2-90a2-a6da275e6460" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedBalanceSheetTableTextBlock_317fb44d-fb0d-4811-9392-bf94d8eaeb57" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScheduleOfCondensedBalanceSheetTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e19ce96-2305-45c2-90a2-a6da275e6460" xlink:to="loc_srt_ScheduleOfCondensedBalanceSheetTableTextBlock_317fb44d-fb0d-4811-9392-bf94d8eaeb57" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedIncomeStatementTableTextBlock_678ee767-7db5-4579-98b1-f0fbc8a6abfc" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScheduleOfCondensedIncomeStatementTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e19ce96-2305-45c2-90a2-a6da275e6460" xlink:to="loc_srt_ScheduleOfCondensedIncomeStatementTableTextBlock_678ee767-7db5-4579-98b1-f0fbc8a6abfc" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedCashFlowStatementTableTextBlock_003e8d3d-13be-46c9-ad66-c62f49037395" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScheduleOfCondensedCashFlowStatementTableTextBlock"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e19ce96-2305-45c2-90a2-a6da275e6460" xlink:to="loc_srt_ScheduleOfCondensedCashFlowStatementTableTextBlock_003e8d3d-13be-46c9-ad66-c62f49037395" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_1379ca4f-72cc-404d-9d8e-a7f9950e2602" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_3e19ce96-2305-45c2-90a2-a6da275e6460" xlink:to="loc_us-gaap_StatementTable_1379ca4f-72cc-404d-9d8e-a7f9950e2602" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_d0c8b144-10ac-478f-8474-0444d4f198c4" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_1379ca4f-72cc-404d-9d8e-a7f9950e2602" xlink:to="loc_dei_LegalEntityAxis_d0c8b144-10ac-478f-8474-0444d4f198c4" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_d0c8b144-10ac-478f-8474-0444d4f198c4_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_d0c8b144-10ac-478f-8474-0444d4f198c4" xlink:to="loc_dei_EntityDomain_d0c8b144-10ac-478f-8474-0444d4f198c4_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_d2f223cc-368d-45e5-b790-928ef24cb62f" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_d0c8b144-10ac-478f-8474-0444d4f198c4" xlink:to="loc_dei_EntityDomain_d2f223cc-368d-45e5-b790-928ef24cb62f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_db0d2c8d-565c-45d1-8632-123374643eaa" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_d2f223cc-368d-45e5-b790-928ef24cb62f" xlink:to="loc_sum_SummitMaterialsLlcMember_db0d2c8d-565c-45d1-8632-123374643eaa" xlink:type="arc" order="0"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingBalanceSheetsDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingBalanceSheetsDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingBalanceSheetsDetails" xlink:type="extended" id="idca51999b55043879df3406291732d4f_GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingBalanceSheetsDetails">
<link:loc xlink:type="locator" xlink:label="loc_srt_CondensedFinancialStatementsCaptionsLineItems_04876a1b-9ddf-42ce-9ada-3e81871e9d7b" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CondensedFinancialStatementsCaptionsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_a2a9fe5f-fd05-4049-93d7-cc81cb9df64b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_04876a1b-9ddf-42ce-9ada-3e81871e9d7b" xlink:to="loc_us-gaap_AssetsAbstract_a2a9fe5f-fd05-4049-93d7-cc81cb9df64b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_e6e08721-9e90-4d5d-8994-f4db193fdde2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrentAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_a2a9fe5f-fd05-4049-93d7-cc81cb9df64b" xlink:to="loc_us-gaap_AssetsCurrentAbstract_e6e08721-9e90-4d5d-8994-f4db193fdde2" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_149108b8-d6db-4541-81f7-b309fbd64234" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_e6e08721-9e90-4d5d-8994-f4db193fdde2" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_149108b8-d6db-4541-81f7-b309fbd64234" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_e7ec2174-2b99-460e-a020-e2313a251e87" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableNetCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_e6e08721-9e90-4d5d-8994-f4db193fdde2" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_e7ec2174-2b99-460e-a020-e2313a251e87" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_IntercompanyReceivablesAssetsCurrent_8b7f82b2-52ac-4fe5-bda4-8b78117e9f69" xlink:href="sum-20220702.xsd#sum_IntercompanyReceivablesAssetsCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_e6e08721-9e90-4d5d-8994-f4db193fdde2" xlink:to="loc_sum_IntercompanyReceivablesAssetsCurrent_8b7f82b2-52ac-4fe5-bda4-8b78117e9f69" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNetCurrent_41eefb45-1447-45a2-bf98-d749a76bb678" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerAssetNetCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_e6e08721-9e90-4d5d-8994-f4db193fdde2" xlink:to="loc_us-gaap_ContractWithCustomerAssetNetCurrent_41eefb45-1447-45a2-bf98-d749a76bb678" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_8f60aa95-0060-4c29-afb2-5f7da1e2abcf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InventoryNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_e6e08721-9e90-4d5d-8994-f4db193fdde2" xlink:to="loc_us-gaap_InventoryNet_8f60aa95-0060-4c29-afb2-5f7da1e2abcf" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_OtherAssetsAndAssetsHeldForSaleCurrent_2b024fb1-6c24-40de-b193-6a19da63943f" xlink:href="sum-20220702.xsd#sum_OtherAssetsAndAssetsHeldForSaleCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_e6e08721-9e90-4d5d-8994-f4db193fdde2" xlink:to="loc_sum_OtherAssetsAndAssetsHeldForSaleCurrent_2b024fb1-6c24-40de-b193-6a19da63943f" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_fe7ccb01-fe8c-41f9-aacd-b05e5c512477" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_e6e08721-9e90-4d5d-8994-f4db193fdde2" xlink:to="loc_us-gaap_AssetsCurrent_fe7ccb01-fe8c-41f9-aacd-b05e5c512477" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_89f5039c-3677-4251-9c3f-712178d0e365" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_a2a9fe5f-fd05-4049-93d7-cc81cb9df64b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_89f5039c-3677-4251-9c3f-712178d0e365" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_107253b7-4d58-4ccc-b261-1472ed2ae4a3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_a2a9fe5f-fd05-4049-93d7-cc81cb9df64b" xlink:to="loc_us-gaap_Goodwill_107253b7-4d58-4ccc-b261-1472ed2ae4a3" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_3405e260-20ca-4d93-9fb9-c352fc3ecf61" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_a2a9fe5f-fd05-4049-93d7-cc81cb9df64b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_3405e260-20ca-4d93-9fb9-c352fc3ecf61" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_8a58a6bd-fdc1-4c6d-93a2-6516b7e1bd1d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_a2a9fe5f-fd05-4049-93d7-cc81cb9df64b" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_8a58a6bd-fdc1-4c6d-93a2-6516b7e1bd1d" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_OtherAssetsAndAssetsHeldForSaleNoncurrent_378713ee-de69-47f6-a40d-0dfbee3203ac" xlink:href="sum-20220702.xsd#sum_OtherAssetsAndAssetsHeldForSaleNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_a2a9fe5f-fd05-4049-93d7-cc81cb9df64b" xlink:to="loc_sum_OtherAssetsAndAssetsHeldForSaleNoncurrent_378713ee-de69-47f6-a40d-0dfbee3203ac" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_5a6437fc-f6f9-4b7d-a923-b0a84d3803b1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_a2a9fe5f-fd05-4049-93d7-cc81cb9df64b" xlink:to="loc_us-gaap_Assets_5a6437fc-f6f9-4b7d-a923-b0a84d3803b1" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_38d3e67d-f532-4b3e-9be2-72448ffee47d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_04876a1b-9ddf-42ce-9ada-3e81871e9d7b" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_38d3e67d-f532-4b3e-9be2-72448ffee47d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_bd397817-598e-4d08-9b3e-ddda6f623862" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_38d3e67d-f532-4b3e-9be2-72448ffee47d" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_bd397817-598e-4d08-9b3e-ddda6f623862" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_e4940eec-4d6a-4b36-8160-4ed7f3bad779" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_bd397817-598e-4d08-9b3e-ddda6f623862" xlink:to="loc_us-gaap_LongTermDebtCurrent_e4940eec-4d6a-4b36-8160-4ed7f3bad779" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AcquisitionRelatedLiabilitiesCurrent_954ce261-3175-41c4-b198-8025917574fd" xlink:href="sum-20220702.xsd#sum_AcquisitionRelatedLiabilitiesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_bd397817-598e-4d08-9b3e-ddda6f623862" xlink:to="loc_sum_AcquisitionRelatedLiabilitiesCurrent_954ce261-3175-41c4-b198-8025917574fd" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_7b8e2af9-d883-4da0-8a08-dddb75f27c54" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsPayableCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_bd397817-598e-4d08-9b3e-ddda6f623862" xlink:to="loc_us-gaap_AccountsPayableCurrent_7b8e2af9-d883-4da0-8a08-dddb75f27c54" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AccruedLiabilitiesCurrentExcludingLiabilitiesHeldForSale_31d1efd5-7e1d-4419-b4b7-2abc4426c998" xlink:href="sum-20220702.xsd#sum_AccruedLiabilitiesCurrentExcludingLiabilitiesHeldForSale"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_bd397817-598e-4d08-9b3e-ddda6f623862" xlink:to="loc_sum_AccruedLiabilitiesCurrentExcludingLiabilitiesHeldForSale_31d1efd5-7e1d-4419-b4b7-2abc4426c998" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_599ad4a0-4864-4321-8959-8a14e69b0a0c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_bd397817-598e-4d08-9b3e-ddda6f623862" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_599ad4a0-4864-4321-8959-8a14e69b0a0c" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_IntercompanyPayablesLiabilitiesCurrent_d0fcd685-aed1-4965-9281-ea565fbd53a8" xlink:href="sum-20220702.xsd#sum_IntercompanyPayablesLiabilitiesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_bd397817-598e-4d08-9b3e-ddda6f623862" xlink:to="loc_sum_IntercompanyPayablesLiabilitiesCurrent_d0fcd685-aed1-4965-9281-ea565fbd53a8" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_e9bc4dc5-29c1-481f-97e8-f1238f6ffba2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_bd397817-598e-4d08-9b3e-ddda6f623862" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_e9bc4dc5-29c1-481f-97e8-f1238f6ffba2" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_375f5653-12d6-4857-b633-25d85096e27a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_bd397817-598e-4d08-9b3e-ddda6f623862" xlink:to="loc_us-gaap_LiabilitiesCurrent_375f5653-12d6-4857-b633-25d85096e27a" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_LongTermDebtNoncurrentNet_b062dc6a-34b4-45ae-ab29-dbf36c8f7a00" xlink:href="sum-20220702.xsd#sum_LongTermDebtNoncurrentNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_38d3e67d-f532-4b3e-9be2-72448ffee47d" xlink:to="loc_sum_LongTermDebtNoncurrentNet_b062dc6a-34b4-45ae-ab29-dbf36c8f7a00" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_AcquisitionRelatedLiabilitiesNonCurrent_0e385dc4-27a5-40ab-a998-f591600eff56" xlink:href="sum-20220702.xsd#sum_AcquisitionRelatedLiabilitiesNonCurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_38d3e67d-f532-4b3e-9be2-72448ffee47d" xlink:to="loc_sum_AcquisitionRelatedLiabilitiesNonCurrent_0e385dc4-27a5-40ab-a998-f591600eff56" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_10db5a01-e0a1-4d26-b2b5-f2f70ae2b895" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_38d3e67d-f532-4b3e-9be2-72448ffee47d" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_10db5a01-e0a1-4d26-b2b5-f2f70ae2b895" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_OtherLiabilitiesAndDisposalGroupIncludingDiscontinuedOperationLiabilitiesNoncurrent_f0e479ac-13e7-4c23-a6c8-37ddfe60f2f9" xlink:href="sum-20220702.xsd#sum_OtherLiabilitiesAndDisposalGroupIncludingDiscontinuedOperationLiabilitiesNoncurrent"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_38d3e67d-f532-4b3e-9be2-72448ffee47d" xlink:to="loc_sum_OtherLiabilitiesAndDisposalGroupIncludingDiscontinuedOperationLiabilitiesNoncurrent_f0e479ac-13e7-4c23-a6c8-37ddfe60f2f9" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_c431e829-fb9c-45cb-99e9-8b33ab66e276" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Liabilities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_38d3e67d-f532-4b3e-9be2-72448ffee47d" xlink:to="loc_us-gaap_Liabilities_c431e829-fb9c-45cb-99e9-8b33ab66e276" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_cfc9575b-55f2-4edb-8620-063494f12c43" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_38d3e67d-f532-4b3e-9be2-72448ffee47d" xlink:to="loc_us-gaap_LimitedLiabilityCompanyLlcMembersEquityIncludingPortionAttributableToNoncontrollingInterest_cfc9575b-55f2-4edb-8620-063494f12c43" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_f0e2ccd2-b892-4f07-a865-3e0acdb5759a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_38d3e67d-f532-4b3e-9be2-72448ffee47d" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_f0e2ccd2-b892-4f07-a865-3e0acdb5759a" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedFinancialStatementsTable_ff087b3c-e1b2-40ee-9209-dafa8bfc5473" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScheduleOfCondensedFinancialStatementsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_04876a1b-9ddf-42ce-9ada-3e81871e9d7b" xlink:to="loc_srt_ScheduleOfCondensedFinancialStatementsTable_ff087b3c-e1b2-40ee-9209-dafa8bfc5473" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_8b5b4edf-20bb-43cf-a42e-0ca11d87d214" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_ff087b3c-e1b2-40ee-9209-dafa8bfc5473" xlink:to="loc_dei_LegalEntityAxis_8b5b4edf-20bb-43cf-a42e-0ca11d87d214" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_8b5b4edf-20bb-43cf-a42e-0ca11d87d214_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_8b5b4edf-20bb-43cf-a42e-0ca11d87d214" xlink:to="loc_dei_EntityDomain_8b5b4edf-20bb-43cf-a42e-0ca11d87d214_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_c648f33a-22ff-4731-b15e-5f3bff77b43a" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_8b5b4edf-20bb-43cf-a42e-0ca11d87d214" xlink:to="loc_dei_EntityDomain_c648f33a-22ff-4731-b15e-5f3bff77b43a" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_d803375b-0bb6-4f78-9d1f-ec2389f2878b" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_c648f33a-22ff-4731-b15e-5f3bff77b43a" xlink:to="loc_sum_SummitMaterialsLlcMember_d803375b-0bb6-4f78-9d1f-ec2389f2878b" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_3ed24e1a-bb1d-4fb2-bccf-550cb0115d70" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_ff087b3c-e1b2-40ee-9209-dafa8bfc5473" xlink:to="loc_srt_ConsolidatedEntitiesAxis_3ed24e1a-bb1d-4fb2-bccf-550cb0115d70" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_3ed24e1a-bb1d-4fb2-bccf-550cb0115d70_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_3ed24e1a-bb1d-4fb2-bccf-550cb0115d70" xlink:to="loc_srt_ConsolidatedEntitiesDomain_3ed24e1a-bb1d-4fb2-bccf-550cb0115d70_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_cba2d787-d9e3-46a9-8e0c-ea8151b27836" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_3ed24e1a-bb1d-4fb2-bccf-550cb0115d70" xlink:to="loc_srt_ConsolidatedEntitiesDomain_cba2d787-d9e3-46a9-8e0c-ea8151b27836" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiaryIssuerMember_5d0acfbd-5615-4aa9-bde6-10f3234044eb" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SubsidiaryIssuerMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_cba2d787-d9e3-46a9-8e0c-ea8151b27836" xlink:to="loc_srt_SubsidiaryIssuerMember_5d0acfbd-5615-4aa9-bde6-10f3234044eb" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_GuarantorSubsidiariesMember_0d89e7b2-052d-47b0-8297-64941de462ae" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_GuarantorSubsidiariesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_cba2d787-d9e3-46a9-8e0c-ea8151b27836" xlink:to="loc_srt_GuarantorSubsidiariesMember_0d89e7b2-052d-47b0-8297-64941de462ae" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_NonGuarantorSubsidiariesMember_851ebdd7-aa4d-423f-8ad1-5b459553a24c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NonGuarantorSubsidiariesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_cba2d787-d9e3-46a9-8e0c-ea8151b27836" xlink:to="loc_srt_NonGuarantorSubsidiariesMember_851ebdd7-aa4d-423f-8ad1-5b459553a24c" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_0e652590-39df-4012-98cf-8d4875405e56" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_ff087b3c-e1b2-40ee-9209-dafa8bfc5473" xlink:to="loc_srt_ConsolidationItemsAxis_0e652590-39df-4012-98cf-8d4875405e56" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_0e652590-39df-4012-98cf-8d4875405e56_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_0e652590-39df-4012-98cf-8d4875405e56" xlink:to="loc_srt_ConsolidationItemsDomain_0e652590-39df-4012-98cf-8d4875405e56_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_9be932a3-6016-4a9c-a072-1dc477d54c3f" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_0e652590-39df-4012-98cf-8d4875405e56" xlink:to="loc_srt_ConsolidationItemsDomain_9be932a3-6016-4a9c-a072-1dc477d54c3f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ReportableLegalEntitiesMember_483454e2-9810-41da-8750-9c4354e87ff0" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ReportableLegalEntitiesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_9be932a3-6016-4a9c-a072-1dc477d54c3f" xlink:to="loc_srt_ReportableLegalEntitiesMember_483454e2-9810-41da-8750-9c4354e87ff0" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationEliminationsMember_e95d68b9-6285-4034-8d3f-70338c592370" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationEliminationsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_9be932a3-6016-4a9c-a072-1dc477d54c3f" xlink:to="loc_srt_ConsolidationEliminationsMember_e95d68b9-6285-4034-8d3f-70338c592370" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingStatementsofOperationsDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingStatementsofOperationsDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingStatementsofOperationsDetails" xlink:type="extended" id="i906e8d98eaec4d56a88b6a4723dba37e_GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingStatementsofOperationsDetails">
<link:loc xlink:type="locator" xlink:label="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CondensedFinancialStatementsCaptionsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_d064de79-cbba-4053-bf46-61e0638cd2ee" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_d064de79-cbba-4053-bf46-61e0638cd2ee" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_46ad01fb-839c-4c40-95e8-b724cd735267" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_46ad01fb-839c-4c40-95e8-b724cd735267" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_GeneralAdministrativeAndOtherExpenses_9ae3157e-be7f-4558-9d3e-d52512ca0a11" xlink:href="sum-20220702.xsd#sum_GeneralAdministrativeAndOtherExpenses"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_sum_GeneralAdministrativeAndOtherExpenses_9ae3157e-be7f-4558-9d3e-d52512ca0a11" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_DepreciationDepletionAmortizationAndAccretion_218da7ca-1e47-4d64-9722-124499d47cdd" xlink:href="sum-20220702.xsd#sum_DepreciationDepletionAmortizationAndAccretion"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_sum_DepreciationDepletionAmortizationAndAccretion_218da7ca-1e47-4d64-9722-124499d47cdd" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_20fec0f3-6ed1-41a9-824f-cdbaeedd8e4a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingIncomeLoss"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_us-gaap_OperatingIncomeLoss_20fec0f3-6ed1-41a9-824f-cdbaeedd8e4a" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_34f0adda-e7c8-4a98-affd-3c7caf1f680b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_34f0adda-e7c8-4a98-affd-3c7caf1f680b" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_fda2adf2-85dd-4643-8c93-8c05c1f5d9e1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestIncomeExpenseNet"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_fda2adf2-85dd-4643-8c93-8c05c1f5d9e1" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_b94c132c-3d65-44f1-960f-185dcc823441" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_b94c132c-3d65-44f1-960f-185dcc823441" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_4a441cff-93f9-4681-9774-0433b3987c37" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_4a441cff-93f9-4681-9774-0433b3987c37" xlink:type="arc" order="8"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_ee0d4f06-02a5-4e3f-a6bb-448a257bb25b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_ee0d4f06-02a5-4e3f-a6bb-448a257bb25b" xlink:type="arc" order="9"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_f71c9604-314a-4303-b4cd-9a528b3609e4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_f71c9604-314a-4303-b4cd-9a528b3609e4" xlink:type="arc" order="10"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_2e0160ae-4a0a-4baa-9a13-09a2ddd4cd41" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_2e0160ae-4a0a-4baa-9a13-09a2ddd4cd41" xlink:type="arc" order="11"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedFinancialStatementsTable_3a28bbeb-e43d-47b2-814c-9f0f237855e6" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScheduleOfCondensedFinancialStatementsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_a3910136-cac1-4c4a-aba7-2ec993ad87a0" xlink:to="loc_srt_ScheduleOfCondensedFinancialStatementsTable_3a28bbeb-e43d-47b2-814c-9f0f237855e6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_29807075-ed38-4b10-b36c-b59aa5eabfda" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_3a28bbeb-e43d-47b2-814c-9f0f237855e6" xlink:to="loc_srt_ConsolidatedEntitiesAxis_29807075-ed38-4b10-b36c-b59aa5eabfda" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_29807075-ed38-4b10-b36c-b59aa5eabfda_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_29807075-ed38-4b10-b36c-b59aa5eabfda" xlink:to="loc_srt_ConsolidatedEntitiesDomain_29807075-ed38-4b10-b36c-b59aa5eabfda_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_8e8eba66-8361-432f-8fa3-897888776e56" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_29807075-ed38-4b10-b36c-b59aa5eabfda" xlink:to="loc_srt_ConsolidatedEntitiesDomain_8e8eba66-8361-432f-8fa3-897888776e56" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiaryIssuerMember_88f178c3-df01-4fc0-a67f-5052c338107e" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SubsidiaryIssuerMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_8e8eba66-8361-432f-8fa3-897888776e56" xlink:to="loc_srt_SubsidiaryIssuerMember_88f178c3-df01-4fc0-a67f-5052c338107e" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_GuarantorSubsidiariesMember_f8b29cbc-b424-407f-873e-2467ae3c5b72" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_GuarantorSubsidiariesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_8e8eba66-8361-432f-8fa3-897888776e56" xlink:to="loc_srt_GuarantorSubsidiariesMember_f8b29cbc-b424-407f-873e-2467ae3c5b72" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_NonGuarantorSubsidiariesMember_64ecda6c-a7a7-42e9-8e22-5e8f7070a9c0" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NonGuarantorSubsidiariesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_8e8eba66-8361-432f-8fa3-897888776e56" xlink:to="loc_srt_NonGuarantorSubsidiariesMember_64ecda6c-a7a7-42e9-8e22-5e8f7070a9c0" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_26435797-0532-4f1f-be5d-7829710d77ff" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_3a28bbeb-e43d-47b2-814c-9f0f237855e6" xlink:to="loc_dei_LegalEntityAxis_26435797-0532-4f1f-be5d-7829710d77ff" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_26435797-0532-4f1f-be5d-7829710d77ff_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_26435797-0532-4f1f-be5d-7829710d77ff" xlink:to="loc_dei_EntityDomain_26435797-0532-4f1f-be5d-7829710d77ff_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_aea1977b-0008-4608-94b7-18a67d70102e" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_26435797-0532-4f1f-be5d-7829710d77ff" xlink:to="loc_dei_EntityDomain_aea1977b-0008-4608-94b7-18a67d70102e" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_9346e550-f202-4a64-ade0-9b633ac227a1" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_aea1977b-0008-4608-94b7-18a67d70102e" xlink:to="loc_sum_SummitMaterialsLlcMember_9346e550-f202-4a64-ade0-9b633ac227a1" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_e0174263-a17e-4498-b45f-7054f4f56fb0" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_3a28bbeb-e43d-47b2-814c-9f0f237855e6" xlink:to="loc_srt_ConsolidationItemsAxis_e0174263-a17e-4498-b45f-7054f4f56fb0" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_e0174263-a17e-4498-b45f-7054f4f56fb0_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_e0174263-a17e-4498-b45f-7054f4f56fb0" xlink:to="loc_srt_ConsolidationItemsDomain_e0174263-a17e-4498-b45f-7054f4f56fb0_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_b2f83747-ff7e-4431-9e9c-889e4b2ea417" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_e0174263-a17e-4498-b45f-7054f4f56fb0" xlink:to="loc_srt_ConsolidationItemsDomain_b2f83747-ff7e-4431-9e9c-889e4b2ea417" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ReportableLegalEntitiesMember_7eb5ca93-fecf-4421-be51-9e7d40b0b58f" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ReportableLegalEntitiesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_b2f83747-ff7e-4431-9e9c-889e4b2ea417" xlink:to="loc_srt_ReportableLegalEntitiesMember_7eb5ca93-fecf-4421-be51-9e7d40b0b58f" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationEliminationsMember_c676b021-b6a1-4f52-b67a-11f446047c48" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationEliminationsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_b2f83747-ff7e-4431-9e9c-889e4b2ea417" xlink:to="loc_srt_ConsolidationEliminationsMember_c676b021-b6a1-4f52-b67a-11f446047c48" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://www.summitmaterials.com/role/GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingStatementsofCashFlowsDetails" xlink:type="simple" xlink:href="sum-20220702.xsd#GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingStatementsofCashFlowsDetails"/>
<link:definitionLink xlink:role="http://www.summitmaterials.com/role/GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingStatementsofCashFlowsDetails" xlink:type="extended" id="i807cc6c41d074a00ab8dd9d1c9c26452_GUARANTORANDNONGUARANTORFINANCIALINFORMATIONScheduleofCondensedConsolidatingStatementsofCashFlowsDetails">
<link:loc xlink:type="locator" xlink:label="loc_srt_CondensedFinancialStatementsCaptionsLineItems_9cf7f4af-0efd-4e5e-9520-f9e5688b1eb1" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CondensedFinancialStatementsCaptionsLineItems"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_bdc3a6bb-358a-487f-8707-f311a30b0c75" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_9cf7f4af-0efd-4e5e-9520-f9e5688b1eb1" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_bdc3a6bb-358a-487f-8707-f311a30b0c75" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7a911485-e9da-4aec-9472-97089bf4da82" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_9cf7f4af-0efd-4e5e-9520-f9e5688b1eb1" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7a911485-e9da-4aec-9472-97089bf4da82" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_68e3a970-944d-404c-be02-49ac62e0e22f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7a911485-e9da-4aec-9472-97089bf4da82" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_68e3a970-944d-404c-be02-49ac62e0e22f" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_c8c63b88-13ea-45a6-9cbe-6774790efcf4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7a911485-e9da-4aec-9472-97089bf4da82" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_c8c63b88-13ea-45a6-9cbe-6774790efcf4" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_43ea9ade-e638-4eac-aaa7-ce205d8b12cb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7a911485-e9da-4aec-9472-97089bf4da82" xlink:to="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_43ea9ade-e638-4eac-aaa7-ce205d8b12cb" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_2d434e7b-8026-4bde-9e13-e1fb3389a3d5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7a911485-e9da-4aec-9472-97089bf4da82" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_2d434e7b-8026-4bde-9e13-e1fb3389a3d5" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_9e2903bd-0785-49fe-9ffe-878991d66171" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7a911485-e9da-4aec-9472-97089bf4da82" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_9e2903bd-0785-49fe-9ffe-878991d66171" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_9a98c22c-4b35-43ed-8c24-d9fcd7ae6da5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_7a911485-e9da-4aec-9472-97089bf4da82" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_9a98c22c-4b35-43ed-8c24-d9fcd7ae6da5" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_37ca0ce8-5ea2-41fc-a30e-02fd899e0f2a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_9cf7f4af-0efd-4e5e-9520-f9e5688b1eb1" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_37ca0ce8-5ea2-41fc-a30e-02fd899e0f2a" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_ProceedsFromRepaymentsOfPartnershipContribution_550b5d17-806e-4b14-994c-4f7b5531ef03" xlink:href="sum-20220702.xsd#sum_ProceedsFromRepaymentsOfPartnershipContribution"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_37ca0ce8-5ea2-41fc-a30e-02fd899e0f2a" xlink:to="loc_sum_ProceedsFromRepaymentsOfPartnershipContribution_550b5d17-806e-4b14-994c-4f7b5531ef03" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfRelatedPartyDebt_eaf63b3e-28d5-4e55-8712-dff3c8e5ef56" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromRepaymentsOfRelatedPartyDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_37ca0ce8-5ea2-41fc-a30e-02fd899e0f2a" xlink:to="loc_us-gaap_ProceedsFromRepaymentsOfRelatedPartyDebt_eaf63b3e-28d5-4e55-8712-dff3c8e5ef56" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfDebt_3feb30f7-04e4-43bb-a0cc-4eaf93b9d407" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfDebt"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_37ca0ce8-5ea2-41fc-a30e-02fd899e0f2a" xlink:to="loc_us-gaap_RepaymentsOfDebt_3feb30f7-04e4-43bb-a0cc-4eaf93b9d407" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfMergerRelatedCostsFinancingActivities_934cd60b-5678-4f18-b17d-94ab619d3036" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfMergerRelatedCostsFinancingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_37ca0ce8-5ea2-41fc-a30e-02fd899e0f2a" xlink:to="loc_us-gaap_PaymentsOfMergerRelatedCostsFinancingActivities_934cd60b-5678-4f18-b17d-94ab619d3036" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDistributionsToAffiliates_2f9e6d8d-dde1-4941-acb8-91c12fc563c1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfDistributionsToAffiliates"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_37ca0ce8-5ea2-41fc-a30e-02fd899e0f2a" xlink:to="loc_us-gaap_PaymentsOfDistributionsToAffiliates_2f9e6d8d-dde1-4941-acb8-91c12fc563c1" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_214a26fe-e842-487e-a926-ba332ffc6b79" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_37ca0ce8-5ea2-41fc-a30e-02fd899e0f2a" xlink:to="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_214a26fe-e842-487e-a926-ba332ffc6b79" xlink:type="arc" order="6"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_e99338ea-5413-4011-853e-240781fa9d8e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_37ca0ce8-5ea2-41fc-a30e-02fd899e0f2a" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_e99338ea-5413-4011-853e-240781fa9d8e" xlink:type="arc" order="7"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_203b6452-00f2-42b5-8859-f6f8923b6fba" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_9cf7f4af-0efd-4e5e-9520-f9e5688b1eb1" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_203b6452-00f2-42b5-8859-f6f8923b6fba" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_2256f092-cfe8-4c09-955b-0d37d3978540" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_9cf7f4af-0efd-4e5e-9520-f9e5688b1eb1" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_2256f092-cfe8-4c09-955b-0d37d3978540" xlink:type="arc" order="4"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_e61d2ec1-b8e7-4819-9f86-e4764c79bf25" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_9cf7f4af-0efd-4e5e-9520-f9e5688b1eb1" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_e61d2ec1-b8e7-4819-9f86-e4764c79bf25" xlink:type="arc" order="5"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_9fcc85e9-7096-4a75-8fbb-3662a3a0a9b7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfCondensedFinancialStatementsTable_9db84446-083a-4c9c-9d0f-dbfaa1bbc4fc" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScheduleOfCondensedFinancialStatementsTable"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedFinancialStatementsCaptionsLineItems_9cf7f4af-0efd-4e5e-9520-f9e5688b1eb1" xlink:to="loc_srt_ScheduleOfCondensedFinancialStatementsTable_9db84446-083a-4c9c-9d0f-dbfaa1bbc4fc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_52c7cb30-0720-4358-8d7a-c9423ad576e1" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_LegalEntityAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_9db84446-083a-4c9c-9d0f-dbfaa1bbc4fc" xlink:to="loc_dei_LegalEntityAxis_52c7cb30-0720-4358-8d7a-c9423ad576e1" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_52c7cb30-0720-4358-8d7a-c9423ad576e1_default" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_52c7cb30-0720-4358-8d7a-c9423ad576e1" xlink:to="loc_dei_EntityDomain_52c7cb30-0720-4358-8d7a-c9423ad576e1_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5e0fedd5-9748-4c47-be32-59013e247c95" xlink:href="https://xbrl.sec.gov/dei/2022/dei-2022.xsd#dei_EntityDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_52c7cb30-0720-4358-8d7a-c9423ad576e1" xlink:to="loc_dei_EntityDomain_5e0fedd5-9748-4c47-be32-59013e247c95" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_sum_SummitMaterialsLlcMember_e62076be-3db9-4222-ae9b-7556abde08c7" xlink:href="sum-20220702.xsd#sum_SummitMaterialsLlcMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5e0fedd5-9748-4c47-be32-59013e247c95" xlink:to="loc_sum_SummitMaterialsLlcMember_e62076be-3db9-4222-ae9b-7556abde08c7" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_3f1979c8-29c3-41a6-8d2d-2481749e13c2" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_9db84446-083a-4c9c-9d0f-dbfaa1bbc4fc" xlink:to="loc_srt_ConsolidatedEntitiesAxis_3f1979c8-29c3-41a6-8d2d-2481749e13c2" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_3f1979c8-29c3-41a6-8d2d-2481749e13c2_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_3f1979c8-29c3-41a6-8d2d-2481749e13c2" xlink:to="loc_srt_ConsolidatedEntitiesDomain_3f1979c8-29c3-41a6-8d2d-2481749e13c2_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_886cf701-647b-41ae-9492-c88a6de11e5c" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidatedEntitiesDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_3f1979c8-29c3-41a6-8d2d-2481749e13c2" xlink:to="loc_srt_ConsolidatedEntitiesDomain_886cf701-647b-41ae-9492-c88a6de11e5c" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiaryIssuerMember_1ca9823f-ffaa-41e3-bd9f-c73004d41603" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_SubsidiaryIssuerMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_886cf701-647b-41ae-9492-c88a6de11e5c" xlink:to="loc_srt_SubsidiaryIssuerMember_1ca9823f-ffaa-41e3-bd9f-c73004d41603" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_GuarantorSubsidiariesMember_6e5afc25-92c0-46ee-809d-c82353e4548d" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_GuarantorSubsidiariesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_886cf701-647b-41ae-9492-c88a6de11e5c" xlink:to="loc_srt_GuarantorSubsidiariesMember_6e5afc25-92c0-46ee-809d-c82353e4548d" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_NonGuarantorSubsidiariesMember_f30e807a-c885-4fc7-9016-3dd5f279ba2a" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NonGuarantorSubsidiariesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_886cf701-647b-41ae-9492-c88a6de11e5c" xlink:to="loc_srt_NonGuarantorSubsidiariesMember_f30e807a-c885-4fc7-9016-3dd5f279ba2a" xlink:type="arc" order="2"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_a5faa0ef-7538-4f5b-84e6-a99e30f241a4" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsAxis"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ScheduleOfCondensedFinancialStatementsTable_9db84446-083a-4c9c-9d0f-dbfaa1bbc4fc" xlink:to="loc_srt_ConsolidationItemsAxis_a5faa0ef-7538-4f5b-84e6-a99e30f241a4" xlink:type="arc" order="3"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_a5faa0ef-7538-4f5b-84e6-a99e30f241a4_default" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_a5faa0ef-7538-4f5b-84e6-a99e30f241a4" xlink:to="loc_srt_ConsolidationItemsDomain_a5faa0ef-7538-4f5b-84e6-a99e30f241a4_default" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_e954505c-aa74-499a-a7ec-95596723bcd2" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationItemsDomain"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_a5faa0ef-7538-4f5b-84e6-a99e30f241a4" xlink:to="loc_srt_ConsolidationItemsDomain_e954505c-aa74-499a-a7ec-95596723bcd2" xlink:type="arc" order="1"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ReportableLegalEntitiesMember_1b0e1394-2328-4774-88d1-7f9302e3ca28" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ReportableLegalEntitiesMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_e954505c-aa74-499a-a7ec-95596723bcd2" xlink:to="loc_srt_ReportableLegalEntitiesMember_1b0e1394-2328-4774-88d1-7f9302e3ca28" xlink:type="arc" order="0"/>
<link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationEliminationsMember_ae580fa6-7de0-4dde-89f7-67c64537d6be" xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ConsolidationEliminationsMember"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_e954505c-aa74-499a-a7ec-95596723bcd2" xlink:to="loc_srt_ConsolidationEliminationsMember_ae580fa6-7de0-4dde-89f7-67c64537d6be" xlink:type="arc" order="1"/>
</link:definitionLink>
<link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-roles-2022.xsd#eedm"/>
<link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsAbstract"/>
<link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
<link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization" xlink:type="arc" order="0"/>
</link:definitionLink>
</link:linkbase>

1 Subsequent Filing that References this Filing

  As Of               Filer                 Filing    For·On·As Docs:Size             Issuer                      Filing Agent

 1/06/23  Summit Materials, Inc.            S-3ASR      1/06/23    4:372K                                   Workiva Inc Wde… FA01/FA

3 Previous Filings that this Filing References

  As Of               Filer                 Filing    For·On·As Docs:Size             Issuer                      Filing Agent

 5/19/21  Summit Materials, Inc.            8-K:3,5,7,9 5/19/21   17:1.2M                                   Workiva Inc Wde… FA01/FA
10/30/19  Summit Materials, Inc.            10-Q        9/28/19   89:21M                                    Workiva Inc Wde… FA01/FA
 3/27/13  Kilgore Companies, LLC            S-4¶                 116:11M                                    Donnelley … Solutions/FA
↑Top
Filing Submission 0001628280-22-020918   –   Alternative Formats (Word / Rich Text, HTML, Plain Text, et al.)
Copyright © 2024 Fran Finnegan & Company LLC – All Rights Reserved.
About — Privacy — Redactions — Help — Mon., May 6, 12:26:11.2am ET