Document:

EX-10.3

 Exhibit 10.3 

EXCHANGE AGREEMENT 

EXCHANGE AGREEMENT (this “Agreement”), dated as of
[            ], 2015, among Summit Materials, Inc., a Delaware corporation, Summit Materials Holdings L.P., a Delaware limited partnership, and the holders of LP Units (as defined herein)
from time to time party hereto. 
 WHEREAS, the parties hereto desire to provide for the exchange of LP Units for shares of Class A
Common Stock (as defined herein), on the terms and subject to the conditions set forth herein. 
 NOW, THEREFORE, in consideration of the
mutual covenants and undertakings contained herein and for good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto hereby agree as follows: 

ARTICLE I 

SECTION 1.1. Definitions 

The following definitions shall be for all purposes, unless otherwise clearly indicated to the contrary, applied to the terms used in this
Agreement. 
 “Agreement” has the meaning set forth in the preamble of this Agreement. 

“Class A Common Stock” means the Class A common stock, par value $0.01 per share, of the Corporation. 

“Class B Common Stock” means the Class B common stock, par value $0.01 per share, of the Corporation. 

“Code” means the Internal Revenue Code of 1986, as amended. 

“Corporation” means Summit Materials, Inc., a Delaware corporation, and any successor thereto. 

“Exchange” has the meaning set forth in Section 2.1(a) hereof. 

“Exchange Rate” means, at any time, the number of shares of Class A Common Stock for which a LP Unit is entitled
to be exchanged at such time. On the date of this Agreement, the Exchange Rate shall be 1 for 1, subject to adjustment pursuant to Section 2.2 hereof. 

“Financial Sponsor Holders” means the affiliates of The Blackstone Group L.P. identified as the Financial Sponsor
Holders on the signature pages hereto and Permitted Transferees thereof. 
 “IPO” has the meaning set forth in
Section 2.1(b) hereof. 
 “LP Unit” means (i) each Class A Unit (as such term is defined in
the Summit Holdings LP Agreement) issued as of the date hereof and (ii) each Class A Unit or other interest in Summit Holdings that may be issued by Summit Holdings in the future that is designated by the Corporation as a “LP
Unit.” 

 “LP Unitholder” means each holder of one or more LP Units that may from
time to time be a party to this Agreement. 
 “Permitted Transferee” has the meaning given to such term in
Section 3.1 hereof. 
 “Securities Act” has the meaning set forth in Section 2.1(f) hereof.

 “Summit Holdings” means Summit Materials Holdings L.P., a Delaware limited partnership, and any successor
thereto. 
 “Summit Holdco” means Summit Owner Holdco, LLC, a Delaware limited liability company, and any successor
thereto. 
 “Summit Holdings LP Agreement” means the Fourth Amended and Restated Limited Partnership Agreement of
Summit Holdings, dated on or about the date hereof, as such agreement may be amended from time to time. 
 “Unvested
Units” has the meaning given to such term in the Summit Holdings LP Agreement. 
 ARTICLE II 

SECTION 2.1. Exchange of LP Units for Class A Common Stock. 

(a) Each Financial Sponsor Holder shall be entitled at any time and from time to time, upon the terms and subject to the conditions hereof, to
surrender LP Units (other than Unvested Units) to the Corporation, for the account of Summit Holdings, in exchange for the delivery to the exchanging Financial Sponsor Holder of a number of shares of Class A Common Stock that is equal to the
product of the number of LP Units surrendered multiplied by the Exchange Rate (such exchange, an “Exchange”); provided that any such Exchange is for a minimum of the lesser of 1,000 LP Units or all of the LP
Units (other than Unvested Units) held by such Financial Sponsor Holder. 
 (b) Each LP Unitholder that is not a Financial Sponsor Holder
shall be entitled from and after the first anniversary of the date of the closing of the initial public offering and sale of Class A Common Stock (as contemplated by the Corporation’s Registration Statement on Form S-1 (File
No. 333-201058)) (the “IPO”), or, if later, the date of the initial filing by the Corporation of a registration statement with the U.S. Securities and Exchange Commission to cover delivery of shares of Class A
Common Stock to LP Unitholders upon an Exchange (as defined herein) of LP Units (other than Unvested Units), at any time and from time to time, upon the terms and subject to the conditions hereof to elect to effect an Exchange; provided that
any such Exchange is for a minimum of the lesser of 1,000 LP Units or all of the LP Units (other than Unvested Units) held by such LP Unitholder. 

 (c) An LP Unitholder shall exercise its right to exchange LP Units as set forth in
Section 2.1(a) or Section 2.1(b) hereof, as applicable, by delivering to the Corporation and to Summit Holdings a written election of exchange in respect of the LP Units to be exchanged substantially in the form of Exhibit
A hereto and any certificates, if any, representing LP Units, duly executed by such holder or such holder’s duly authorized attorney, in each case delivered during normal business hours at the principal executive offices of the Corporation
and of Summit Holdings. As promptly as practicable following the delivery of such a written election of exchange, Summit Holdings shall deliver or cause to be delivered at the offices of the then-acting registrar and transfer agent of the
Class A Common Stock or, if there is no then-acting registrar and transfer agent of the Class A Common Stock, at the principal executive offices of the Corporation, the number of shares of Class A Common Stock deliverable upon such
Exchange, registered in the name of the relevant exchanging LP Unitholder. To the extent the Class A Common Stock is settled through the facilities of The Depository Trust Company, and the exchanging LP Unitholder is permitted to hold shares of
Class A Common Stock through The Depository Trust Company, Summit Holdings will, subject to Section 2.1(d) hereof, upon the written instruction of an exchanging LP Unitholder, use its reasonable best efforts to deliver or cause to
be delivered the shares of Class A Common Stock deliverable to such exchanging LP Unitholder, through the facilities of The Depository Trust Company, to the account of the participant of The Depository Trust Company designated by such
exchanging LP Unitholder. The Corporation shall take such actions as may be required to ensure the performance by Summit Holdings of its obligations under this Section 2.1(c) and Section 2.1(a) and Section 2.1(b)
hereof, including the issuance and sale of shares of Class A Common Stock to or for the account of Summit Holdings in exchange for the delivery to the Corporation of a number of LP Units that is equal to the number of LP Units surrendered
by an exchanging LP Unitholder. Any LP Unitholder (other than Summit Holdco) that surrenders all of its LP Units (other than Unvested Units) held by such LP Unitholder to the Corporation, for the account of Summit Holdings, pursuant to this
Section 2.1 shall concurrently surrender all shares of Class B Common Stock held by such LP Unitholder (including any fractions thereof) to the Corporation. 

(d) Summit Holdings and each exchanging LP Unitholder shall bear its own expenses in connection with the consummation of any Exchange, whether
or not any such Exchange is ultimately consummated, except that Summit Holdings shall bear any transfer taxes, stamp taxes or duties, or other similar taxes in connection with, or arising by reason of, any Exchange; provided, however,
that if any shares of Class A Common Stock are to be delivered in a name other than that of the LP Unitholder that requested the Exchange, then such LP Unitholder and/or the person in whose name such shares are to be delivered shall pay to
Summit Holdings the amount of any transfer taxes, stamp taxes or duties, or other similar taxes in connection with, or arising by reason of, such Exchange or shall establish to the reasonable satisfaction of Summit Holdings that such tax has been
paid or is not payable. 
 (e) To the extent the Corporation or Summit Holdings shall determine that LP Units do not meet the requirements
of Treasury Regulation Section 1.7704-1(h), the Corporation or Summit Holdings may impose such restrictions on Exchange as the Corporation or Summit Holdings may reasonably determine to be necessary or advisable so that Summit Holdings is not
treated as a “publicly traded partnership” under Section 7704 of the Code; provided, that each LP Unitholder shall be entitled at any time Exchange LP Units for Class A Common Stock, provided that the aggregate number of
LP Units surrendered by such LP Unitholder in any such Exchange 

 
is greater than 2% of the then-outstanding LP Units (provided that such Exchange constitutes part of a “block transfer” within the meaning of Treasury Regulation
Section 1.7704-1(e)(2)). Notwithstanding anything to the contrary herein, no Exchange shall be permitted (and, if attempted, shall be void ab initio) if, in the good faith determination of the Corporation or of Summit Holdings, such an
Exchange would pose a material risk that Summit Holdings would be a “publicly traded partnership” under Section 7704 of the Code. 

(f) For the avoidance of doubt, and notwithstanding anything to the contrary herein, an LP Unitholder shall not be entitled to exchange LP
Units to the extent the Corporation determines that such Exchange (i) would be prohibited by law or regulation (including, without limitation, the unavailability of any requisite registration statement filed under the U.S. Securities Act of
1933, as amended (the “Securities Act”), or any exemption from the registration requirements thereunder) or (ii) would not be permitted under any other agreements with the Corporation or its subsidiaries to which such LP
Unitholder may be party (including, without limitation, the Summit Holdings LP Agreement) or any written policies of the Corporation related to unlawful or inappropriate trading applicable to its directors, officers or other personnel. 

(g) The Corporation may adopt reasonable procedures for the implementation of the exchange provisions set forth in this Article II,
including, without limitation, procedures for the giving of notice of an election of exchange. 
 SECTION 2.2.
Adjustment. 
 (a) The Exchange Rate shall be adjusted accordingly if there is: (a) any subdivision (by any unit split, unit
distribution, reclassification, reorganization, recapitalization or otherwise) or combination (by reverse unit split, reclassification, reorganization, recapitalization or otherwise) of the LP Units that is not accompanied by an identical
subdivision or combination of the Class A Common Stock; or (b) any subdivision (by any stock split, stock dividend or distribution, reclassification, reorganization, recapitalization or otherwise) or combination (by reverse stock split,
reclassification, reorganization, recapitalization or otherwise) of the Class A Common Stock that is not accompanied by an identical subdivision or combination of the LP Units. If there is any reclassification, reorganization, recapitalization
or other similar transaction in which the Class A Common Stock is converted or changed into another security, securities or other property, then upon any subsequent Exchange, an exchanging LP Unitholder shall be entitled to receive the amount
of such security, securities or other property that such exchanging LP Unitholder would have received if such Exchange had occurred immediately prior to the effective date of such reclassification, reorganization, recapitalization or other similar
transaction, taking into account any adjustment as a result of any subdivision (by any split, distribution or dividend, reclassification, reorganization, recapitalization or otherwise) or combination (by reverse split, reclassification,
recapitalization or otherwise) of such security, securities or other property that occurs after the effective time of such reclassification, reorganization, recapitalization or other similar transaction. Except as may be required in the immediately
preceding sentence, no adjustments in respect of distributions shall be made upon the exchange of any LP Unit. 
 SECTION 2.3.
Class A Common Stock to be Issued. 

 (a) The Corporation shall at all times reserve and keep available out of its authorized but
unissued Class A Common Stock, solely for the purpose of issuance upon an Exchange, such number of shares of Class A Common Stock as shall be deliverable upon any such Exchange; provided that nothing contained herein shall be
construed to preclude Summit Holdings from satisfying its obligations in respect of the Exchange of the LP Units by delivery of shares of Class A Common Stock which are held in the treasury of the Corporation or are held by Summit Holdings or
any of their subsidiaries or by delivery of purchased shares of Class A Common Stock (which may or may not be held in the treasury of the Corporation or held by any subsidiary thereof). The Corporation and Summit Holdings covenant that all
Class A Common Stock issued upon an Exchange will, upon issuance, be validly issued, fully paid and non-assessable. 
 (b) The
Corporation and Summit Holdings covenant and agree that, to the extent that a registration statement under the Securities Act is effective and available for shares of Class A Common Stock to be delivered with respect to any Exchange, shares
that have been registered under the Securities Act shall be delivered in respect of such Exchange. In the event that any Exchange in accordance with this Agreement is to be effected at a time when any required registration has not become effective
or otherwise is unavailable, upon the request and with the reasonable cooperation of the LP Unitholder requesting such Exchange, the Corporation and Summit Holdings shall use commercially reasonable efforts to promptly facilitate such Exchange
pursuant to any reasonably available exemption from such registration requirements. The Corporation and Summit Holdings shall use commercially reasonable efforts to list the Class A Common Stock required to be delivered upon exchange prior to
such delivery upon each national securities exchange or inter-dealer quotation system upon which the outstanding Class A Common Stock may be listed or traded at the time of such delivery. 

SECTION 2.4. Restrictions. Any restrictions on transfer under any agreements with the Corporation or any of its
subsidiaries to which an exchanging LP Unitholder may be party shall apply, mutatis mutandis, to any shares of Class A Common Stock. 

ARTICLE III 

SECTION 3.1. Additional LP Unitholders. To the extent an LP Unitholder validly transfers any or all of such
holder’s LP Units to another person in a transaction in accordance with, and not in contravention of, the Summit Holdings LP Agreement or any other agreement or agreements with the Corporation or any of its subsidiaries to which a transferring
LP Unitholder may be party, then such transferee (each, a “Permitted Transferee”) shall have the right to execute and deliver a joinder to this Agreement, substantially in the form of Exhibit B hereto, whereupon
such Permitted Transferee shall become an LP Unitholder hereunder. To the extent Summit Holdings issues LP Units in the future, Summit Holdings shall be entitled, in its sole discretion, to make any holder of such LP Units an LP Unitholder hereunder
through such holder’s execution and delivery of a joinder to this Agreement, substantially in the form of Exhibit B hereto. 

 SECTION 3.2. Addresses and Notices. All notices, requests, claims, demands and
other communications hereunder shall be in writing and shall be given (and shall be deemed to have been duly given upon receipt) by delivery in person, by courier service, by fax, by electronic mail (delivery receipt requested) or by registered or
certified mail (postage prepaid, return receipt requested) to the respective parties at the following addresses (or at such other address for a party as shall be as specified in a notice given in accordance with this Section 3.2): 

(a) If to the Corporation, to: 

Summit Materials, Inc. 

1550 Wynkoop, 3rd Floor 

Denver, Colorado 80202 

Attention: Chief Legal Officer 

Fax: (303) 893-6993 

Email: Legal@Summit-Materials.com 

(b) If to Summit Holdings, to: 

Summit Materials Holdings L.P. 

c/o Summit Materials, Inc. 

1550 Wynkoop, 3rd Floor 

Denver, Colorado 80202 

Attention: Chief Legal Officer 

Fax: (303) 893-6993 

Email: Legal@Summit-Materials.com 

(c) If to any LP Unitholder, to the address and other contact information set forth in the records of Summit Holdings from time to time. 

SECTION 3.3. Further Action. The parties shall execute and deliver all documents, provide all information and take or
refrain from taking action as may be necessary or appropriate to achieve the purposes of this Agreement. 
 SECTION 3.4. Binding
Effect. This Agreement shall be binding upon and inure to the benefit of all of the parties and, to the extent permitted by this Agreement, their successors, executors, administrators, heirs, legal representatives and assigns. 

SECTION 3.5. Severability. If any term or other provision of this Agreement is held to be invalid, illegal or
incapable of being enforced by any rule of law, or public policy, all other conditions and provisions of this Agreement shall nevertheless remain in full force and effect so long as the economic or legal substance of the transactions is not affected
in any manner materially adverse to any party. Upon a determination that any term or other provision is invalid, illegal or incapable of being enforced, the parties hereto shall negotiate in good faith to modify this Agreement so as to effect the
original intent of the parties as closely as possible in a mutually acceptable manner in order that the transactions contemplated hereby be consummated as originally contemplated to the fullest extent possible. 

 SECTION 3.6. Amendment. The provisions of this Agreement may be amended only
by the affirmative vote or written consent of each of (i) the Corporation, (ii) Summit Holdings, (iii) LP Unitholders holding a majority of the then outstanding LP Units (excluding LP Units held by the Corporation) and (iv) for
so long as the Financial Sponsor Holders collectively own, in the aggregate, at least 5% of the outstanding LP Units, each of the Financial Sponsor Holders. 

SECTION 3.7. Waiver. No failure by any party to insist upon the strict performance of any covenant, duty, agreement or
condition of this Agreement or to exercise any right or remedy consequent upon a breach thereof shall constitute waiver of any such breach of any other covenant, duty, agreement or condition. 

SECTION 3.8. Submission to Jurisdiction; Waiver of Jury Trial. 

(a) Any and all disputes which cannot be settled amicably, including any ancillary claims of any party, arising out of, relating to or in
connection with the validity, negotiation, execution, interpretation, performance or non-performance of this Agreement (including the validity, scope and enforceability of this arbitration provision) shall be
finally settled by arbitration conducted by a single arbitrator in New York in accordance with the then-existing Rules of Arbitration of the International Chamber of Commerce. If the parties to the dispute
fail to agree on the selection of an arbitrator within thirty (30) days of the receipt of the request for arbitration, the International Chamber of Commerce shall make the appointment. The arbitrator shall be a lawyer and shall conduct the
proceedings in the English language. Performance under this Agreement shall continue if reasonably possible during any arbitration proceedings. 

(b) Notwithstanding the provisions of paragraph (a), the parties hereto may bring an action or special proceeding in any court of
competent jurisdiction for the purpose of compelling a party to arbitrate, seeking temporary or preliminary relief in aid of an arbitration hereunder, and/or enforcing an arbitration award and, for the purposes of this paragraph
Section 3.8(b), each party hereto (i) expressly consents to the application of paragraph (c) of this Section 3.8 to any such action or proceeding and (ii) agrees that proof shall not be required that
monetary damages for breach of the provisions of this Agreement would be difficult to calculate and that remedies at law would be inadequate. 

(c)(i) EACH PARTY HERETO IRREVOCABLY SUBMITS TO THE JURISDICTION OF COURTS LOCATED IN NEW YORK, NEW YORK FOR THE PURPOSE OF ANY JUDICIAL
PROCEEDING BROUGHT IN ACCORDANCE WITH THE PROVISIONS OF THIS SECTION 3.8, OR ANY JUDICIAL PROCEEDING ANCILLARY TO AN ARBITRATION OR CONTEMPLATED ARBITRATION ARISING OUT OF OR RELATING TO OR CONCERNING THIS AGREEMENT. Such ancillary
judicial proceedings include any suit, action or proceeding to compel arbitration, to obtain temporary or preliminary judicial relief in aid of arbitration, or to confirm an arbitration award. The parties acknowledge that the fora designated by this
Section 3.8(c) have a reasonable relation to this Agreement and to the parties’ relationship with one another. 

 (ii) The parties hereby waive, to the fullest extent permitted by applicable law, any objection
which they now or hereafter may have to personal jurisdiction or to the laying of venue of any such ancillary suit, action or proceeding brought in any court referred to in this Section 3.8(c), and such parties agree not to plead or
claim the same. 
 SECTION 3.9. Counterparts. This Agreement may be executed and delivered (including by facsimile
transmission or by e-mail delivery of a “.pdf” format data file) in one or more counterparts, and by the different parties hereto in separate counterparts, each of which when executed and delivered shall be deemed to be an original but all
of which taken together shall constitute one and the same agreement. Copies of executed counterparts transmitted by telecopy, by e-mail delivery of a “.pdf” format data file or other electronic transmission service shall be considered
original executed counterparts for purposes of this Section 3.9. 
 SECTION 3.10. Tax Treatment. Solely
for U.S. federal income tax purposes, this Agreement shall be treated as part of the partnership agreement of Summit Holdings as described in Section 761(c) of the Code and Sections 1.704-1(b)(2)(ii)(h) and 1.761-1(c) of the Treasury
Regulations promulgated thereunder. As required by the Code and the Treasury Regulations, the parties shall report any Exchange consummated hereunder as a taxable sale of the LP Units by an LP Unitholder to the Corporation, and no party shall take a
contrary position on any income tax return, amendment thereof or communication with a taxing authority unless an alternate position is permitted under the Code and Treasury Regulations and the Corporation consents in writing. 

SECTION 3.11. Specific Performance. The parties hereto agree that irreparable damage would occur in the event that any
of the provisions of this Agreement were not performed in accordance with their specific terms or were otherwise breached. It is accordingly agreed that the parties shall be entitled to specific performance of the terms and provisions hereof, in
addition to any other remedy to which they are entitled at law or in equity. 
 SECTION 3.12. Independent Nature of LP
Unitholders’ Rights and Obligations. The obligations of each LP Unitholder hereunder are several and not joint with the obligations of any other LP Unitholder, and no LP Unitholder shall be responsible in any way for the
performance of the obligations of any other LP Unitholder hereunder. The decision of each LP Unitholder to enter into to this Agreement has been made by such LP Unitholder independently of any other LP Unitholder. Nothing contained herein, and no
action taken by any LP Unitholder pursuant hereto, shall be deemed to constitute the LP Unitholders as a partnership, an association, a joint venture or any other kind of entity, or create a presumption that the LP Unitholders are in any way acting
in concert or as a group with respect to such obligations or the transactions contemplated hereby. The Corporation acknowledges that the LP Unitholders are not acting in concert or as a group, and the Corporation will not assert any such claim with
respect to such obligations or the transactions contemplated hereby. 
 SECTION 3.13. Applicable Law. This Agreement
shall be governed by, and construed in accordance with, the law of the State of Delaware. 

 [Remainder of Page Intentionally Left Blank] 

 IN WITNESS WHEREOF, the parties have caused this Agreement to be duly executed and delivered, all
as of the date first set forth above. 
  

			
	Corporation:
	
	SUMMIT MATERIALS, INC.
		
	By:	 	 
	Name:	 	
	Title:	 	

  

			
	Summit Holdings:
	
	SUMMIT MATERIALS HOLDINGS L.P.
		
	By:	 	 
	Name:	 	
	Title:	 	

  

			
	Financial Sponsor Holders:
	
	[            ]
		
	By:	 	 
	Name:	 	
	Title:	 	

  

			
	Other LP Unitholders:
	
	[            ]
		
	By:	 	 
	Name:	 	
	Title:	 	

 [Signature Page – Summit Exchange Agreement] 

 EXHIBIT A 

[FORM OF] 
 ELECTION OF
EXCHANGE 
 Summit Materials, Inc. 
 1550 Wynkoop, 3rd
Floor 
 Denver, Colorado 80202 
 Attention: Chief Legal Officer

 Summit Materials Holdings L.P. 
 c/o Summit Materials, Inc.

 1550 Wynkoop, 3rd Floor 
 Denver, Colorado 80202 

Attention: Chief Legal Officer 
 Reference is
hereby made to the Exchange Agreement, dated as of [            ], 2015 (the “Exchange Agreement”), among Summit Materials, Inc., a Delaware corporation, Summit
Materials Holdings L.P., a Delaware limited partnership, and the holders of LP Units from time to time party thereto. Capitalized terms used but not defined herein shall have the meanings given to them in the Exchange Agreement. 

The undersigned LP Unitholder hereby transfers to the Corporation, for the account of Summit Holdings, the number of LP Units set forth below
in exchange for shares of Class A Common Stock to be issued in its name as set forth below, as set forth in the Exchange Agreement. 

Legal Name of LP Unitholder:            
                                         
                          

Address:                   
                                         
                                         
                          

Number of LP Units to be exchanged:         
                                         
     
 The undersigned hereby represents and warrants that (i) the undersigned has full legal capacity to
execute and deliver this Election of Exchange and to perform the undersigned’s obligations hereunder; (ii) this Election of Exchange has been duly executed and delivered by the undersigned and is the legal, valid and binding obligation of
the undersigned enforceable against it in accordance with the terms thereof or hereof, as the case may be, subject to applicable bankruptcy, insolvency and similar laws affecting creditors’ rights generally and the availability of equitable
remedies; (iii) the LP Units subject to this Election of Exchange are being transferred to the Corporation free and clear of any pledge, lien, security interest, encumbrance, equities or claim; and (iv) no consent, approval, authorization,
order, registration or qualification of any third party or with any court or governmental agency or body having jurisdiction over the undersigned or the LP Units subject to this Election of Exchange is required to be obtained by the undersigned for
the transfer of such LP Units to the Corporation. 

 The undersigned hereby irrevocably constitutes and appoints any officer of the Corporation or of
Summit Holdings as the attorney of the undersigned, with full power of substitution and resubstitution in the premises, to do any and all things and to take any and all actions that may be necessary to transfer to the Corporation, for the account of
Summit Holdings, the LP Units subject to this Election of Exchange and to deliver to the undersigned the shares of Class A Common Stock to be delivered in exchange therefor. 

IN WITNESS WHEREOF the undersigned, by authority duly given, has caused this Election of Exchange to be executed and delivered by the
undersigned or by its duly authorized attorney. 
  

			
	  

		
	Name:	 	

 
			
		
	      Dated:	 	  

 EXHIBIT B 

[FORM OF] 
 JOINDER
AGREEMENT 
 This Joinder Agreement (“Joinder Agreement”) is a joinder to the Exchange Agreement, dated as of
[            ], 2015 (the “Exchange Agreement”), among Summit Materials, Inc., a Delaware corporation (the “Corporation”), Summit Materials
Holdings L.P., a Delaware limited partnership, and each of the LP Unitholders from time to time party thereto. Capitalized terms used but not defined in this Joinder Agreement shall have their meanings given to them in the Exchange Agreement. This
Joinder Agreement shall be governed by, and construed in accordance with, the law of the State of Delaware. In the event of any conflict between this Joinder Agreement and the Exchange Agreement, the terms of this Joinder Agreement shall control.

 The undersigned hereby joins and enters into the Exchange Agreement having acquired LP Units in Summit Holdings. By signing and returning
this Joinder Agreement to the Corporation, the undersigned accepts and agrees to be bound by and subject to all of the terms and conditions of and agreements of an LP Unitholder contained in the Exchange Agreement, with all attendant rights, duties
and obligations of an LP Unitholder thereunder. The parties to the Exchange Agreement shall treat the execution and delivery hereof by the undersigned as the execution and delivery of the Exchange Agreement by the undersigned and, upon receipt of
this Joinder Agreement by the Corporation and by Summit Holdings, the signature of the undersigned set forth below shall constitute a counterpart signature to the signature page of the Exchange Agreement. 

 

			
	Name:                                     
                                 	  	
		
	Address for Notices:	  	With copies to:
	  
	  	  

		
	  
	  	  

		
	  
	  	  

		
	Attention:EX-10.4

 Exhibit 10.4 

STOCKHOLDERS’ AGREEMENT 

DATED AS OF [            ], 2015 

AMONG 
 SUMMIT MATERIALS,
INC. 
 AND 
 THE
OTHER PARTIES HERETO 

 Table of Contents 

 

							
	 	 	 	  	Page	 
	 ARTICLE I. INTRODUCTORY MATTERS
	  	 	1	  
			
	 1.1
	 	Defined Terms	  	 	1	  
	 1.2
	 	Construction	  	 	4	  
		
	 ARTICLE II. CORPORATE GOVERNANCE MATTERS
	  	 	4	  
			
	 2.1
	 	Election of Directors	  	 	4	  
		
	 ARTICLE III. INFORMATION; VCOC
	  	 	6	  
			
	 3.1
	 	Books and Records; Access	  	 	6	  
	 3.2
	 	Certain Reports	  	 	6	  
	 3.3
	 	VCOC	  	 	6	  
		
	 ARTICLE IV. ADDITIONAL COVENANTS
	  	 	9	  
			
	 4.1
	 	Pledges	  	 	9	  
	 4.2
	 	Post-Closing Date Mergers	  	 	9	  
		
	 ARTICLE V. GENERAL PROVISIONS
	  	 	10	  
			
	 5.1
	 	Termination	  	 	10	  
	 5.2
	 	Notices	  	 	10	  
	 5.3
	 	Amendment; Waiver	  	 	11	  
	 5.4
	 	Further Assurances	  	 	11	  
	 5.5
	 	Assignment	  	 	11	  
	 5.6
	 	Third Parties	  	 	11	  
	 5.7
	 	Governing Law	  	 	11	  
	 5.8
	 	Jurisdiction; Waiver of Jury Trial	  	 	12	  
	 5.9
	 	Specific Performance	  	 	12	  
	 5.10
	 	Entire Agreement	  	 	12	  
	 5.11
	 	Severability	  	 	12	  
	 5.12
	 	Table of Contents, Headings and Captions	  	 	12	  
	 5.13
	 	Grant of Consent	  	 	12	  
	 5.14
	 	Counterparts	  	 	13	  
	 5.15
	 	Effectiveness	  	 	13	  
	 5.16
	 	No Recourse	  	 	13	  

  
 i 

 STOCKHOLDERS’ AGREEMENT 

This Stockholders’ Agreement is entered into as of [            ], 2015 by
and among Summit Materials, Inc., a Delaware corporation (the “Company”), and each of the other parties identified on the signature pages hereto (the “Investor Parties”). 

RECITALS: 
 WHEREAS, the Company
is currently contemplating an underwritten initial public offering (“IPO”) of shares of its Class A Common Stock (as defined below); and 

WHEREAS, in connection with the IPO, the Company and the Investor Parties wish to set forth certain understandings between such parties,
including with respect to certain governance matters. 
 NOW, THEREFORE, the parties agree as follows: 

ARTICLE I. 
 INTRODUCTORY MATTERS

 1.1 Defined Terms. In addition to the terms defined elsewhere herein, the following terms have the following meanings when
used herein with initial capital letters: 
 “Affiliate” has the meaning set forth in Rule 12b-2 promulgated under the
Exchange Act, as in effect on the date hereof. 
 “Agreement” means this Stockholders’ Agreement, as the same may be
amended, supplemented, restated or otherwise modified from time to time in accordance with the terms hereof. 
 “Beneficially
Own” has the meaning set forth in Rule 13d-3 promulgated under the Exchange Act. 
 “Blackstone Designee” has the
meaning set forth in Section 2.1(b) hereof. 
 “Blackstone Designator” means the Blackstone Party, or any group
of Blackstone Parties collectively, then holding of record a majority of Outstanding Summit Interests held of record by all Blackstone Parties. 

“Blackstone Entities” means the entities comprising the Blackstone Parties and their Affiliates and their respective
successors and Permitted Assigns. 
 “Blackstone Parties” means the entities listed on the signature pages hereto under the
heading “Blackstone Parties” and any other Blackstone Entities that may from time to time become parties hereto. 

“Blocker Investor Parties” means Blackstone SMT Feeder Fund V L.P., a Delaware limited partnership, Blackstone SMT Feeder
Fund (Cayman) V L.P., a Cayman Islands limited partnership, Blackstone SMT Feeder Fund V-AC, a Delaware limited partnership and Blackstone SMT Feeder Fund (Cayman) V-AC L.P., a Cayman Islands limited partnership. 

 “Board” means the board of directors of the Company. 

“Business Day” means a day other than a Saturday, Sunday, federal or New York State holiday or other day on which commercial
banks in New York City are authorized or required by law to close. 
 “Class A Common Stock” means the shares of
Class A common stock, par value $0.01 per share, of the Company, and any other capital stock of the Company into which such stock is reclassified or reconstituted. 

“Class B Common Stock” means the shares of Class B common stock, par value $0.01 per share, of the Company, and any other
capital stock of the Company into which such stock is reclassified or reconstituted. 
 “Closing Date” means the date of
the closing of the IPO. 
 “Common Stock” means collectively the Class A Common Stock and the Class B Common Stock.

 “Company” has the meaning set forth in the Preamble. 

“Control” (including its correlative meanings, “Controlled by” and “under common Control
with”) means possession, directly or indirectly, of the power to direct or cause the direction of management or policies (whether through ownership of securities or partnership or other ownership interests, by contract or otherwise) of a
Person. 
 “Director” means any director of the Company. 

“Exchange Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder,
as the same may be amended from time to time. 
 “Exchange Agreement” means the exchange agreement, dated on or about the
date hereof, among the Company, Summit Holdings and the holders of LP Units of Summit Holdings party thereto, as amended and in effect from time to time. 

“Governmental Authority” means any nation or government, any state or other political subdivision thereof, and any entity
exercising executive, legislative, judicial, regulatory or administrative functions of or pertaining to government. 
 “Investor
Parties” has the meaning set forth in the Preamble. 
 “IPO” has the meaning set forth in the Recitals. 

“Law” means any statute, law, regulation, ordinance, rule, injunction, order, decree, governmental approval, directive,
requirement, or other governmental restriction or any similar form of decision of, or determination by, or any interpretation or administration of any of the foregoing by, any Governmental Authority. 

  
 2 

 “LP Units” means the Class A Units and any other class of units or
interests that is established in Summit Holdings. 
 “Outstanding Summit Interests” means, collectively, (i) the
outstanding shares of Class A Common Stock and (ii) the LP Units held by Persons other than the Company. For purposes of calculating any proportion of Outstanding Summit Interests, the number of Outstanding Summit Interests held by any
Person shall consist of the sum of (a) the number of shares of Class A Common Stock held by such Person and (b) the number of shares of Class A Common Stock such Person would receive upon the exchange of all LP Units held by such
Person in accordance with the Exchange Agreement. 
 “Person” means an individual, a partnership, a corporation, a limited
liability company, an association, a joint stock company, a trust, a joint venture, an unincorporated organization, or other form of business organization, whether or not regarded as a legal entity under applicable Law, or any Governmental Authority
or any department, agency or political subdivision thereof. 
 “Permitted Assigns” means, with respect to a Blackstone
Entity, a Transferee of shares of Common Stock or a Transferee (as defined in the Summit Holdings LP Agreement) that agrees to become party to, and to be bound to the same extent as its Transferor by the terms of, this Agreement. 

“Plan Asset Regulation” has the meaning set forth in Section 3.3(a) hereof. 

“Pre-IPO Owners” means the Blackstone Entities and the other Persons who held Outstanding Summit Interests at the time of the
IPO and any Affiliate thereof that shall become a holder of any Outstanding Summit Interests. 
 “Subsidiary” means, with
respect to any Person, any corporation, limited liability company, partnership, association or other business entity of which: (i) if a corporation, a majority of the total voting power of shares of stock entitled (without regard to the
occurrence of any contingency) to vote in the election of directors, representatives or trustees thereof is at the time owned or Controlled, directly or indirectly, by that Person or one or more of the other Subsidiaries of that Person or a
combination thereof; or (ii) if a limited liability company, partnership, association or other business entity, a majority of the total voting power of stock (or equivalent ownership interest) of the limited liability company, partnership,
association or other business entity is at the time owned or Controlled, directly or indirectly, by that Person or one or more Subsidiaries of that Person or a combination thereof. For purposes hereof, a Person or Persons shall be deemed to have a
majority ownership interest in a limited liability company, partnership, association or other business entity if such Person or Persons shall be allocated a majority of limited liability company, partnership, association or other business entity
gains or losses or shall be or Control the managing member, managing director or other governing body or general partner of such limited liability company, partnership, association or other business entity. 

  
 3 

 “Summit Holdings” means Summit Materials Holdings L.P., a Delaware limited
partnership. 
 “Summit Holdings LP Agreement” means the Fourth Amended and Restated Limited Partnership Agreement of
Summit Holdings, dated on or about the date hereof, as such agreement may be amended from time to time. 
 “Surviving
Company” has the meaning set forth in Section 4.2 hereof 
 “Tax” means any tax or other governmental
fee or like assessment or charge in the nature of a tax that is imposed by any governmental authority, together with any interest, penalty, addition to tax or additional amount imposed by any governmental authority responsible for the imposition of
any such tax. 
 “Tax Receivable Agreement” means the Tax Receivable Agreement, dated as of
[            ], 2015, by and among the Company and certain other parties thereto. 

“Total Number of Directors” means the total number of directors comprising the Board. 

“Transfer” (including its correlative meanings, “Transferor,” “Transferee” and
“Transferred”) shall mean, with respect to any security, directly or indirectly, to sell, contract to sell, give, assign, hypothecate, pledge, encumber, grant a security interest in, offer, sell any option or contract to purchase,
purchase any option or contract to sell, grant any option, right or warrant to purchase, lend or otherwise transfer or dispose of any economic, voting or other rights in or to such security. When used as a noun, “Transfer” shall
have such correlative meaning as the context may require. 
 “VCOC Investor” has the meaning set forth in
Section 3.3(a) hereof. 
 1.2 Construction. The language used in this Agreement will be deemed to be the language
chosen by the parties to express their mutual intent, and no rule of strict construction will be applied against any party. Unless the context otherwise requires: (a) “or” is disjunctive but not exclusive, (b) words in the
singular include the plural, and in the plural include the singular, and (c) the words “hereof,” “herein,” and “hereunder” and words of similar import when used in this Agreement refer to this
Agreement as a whole and not to any particular provision of this Agreement, and Section references are to this Agreement unless otherwise specified. 

ARTICLE II. 
 CORPORATE GOVERNANCE
MATTERS 
 2.1 Election of Directors. 

(a) Following the Closing Date, the Blackstone Designator shall have the right, but not the obligation, to designate, and the individuals
nominated for election as Directors by or at the direction of the Board or a duly-authorized committee thereof shall include, a number of individuals such that, upon the election of each such individual, and each other

  
 4 

 
individual nominated by or at the direction of the Board or a duly-authorized committee of the Board, as a Director and taking into account any Director continuing to serve as such without the
need for re-election, the number of Blackstone Designees (as defined below) serving as Directors of the Company will be equal to: (i) if the Pre-IPO Owners collectively Beneficially Own 50% or more of the total Outstanding Summit Interests as
of the record date for such meeting, the lowest whole number that is greater than 50% of the Total Number of Directors; (ii) if the Pre-IPO Owners collectively Beneficially Own at least 40% (but less than 50%) of the total Outstanding Summit
Interests as of the record date for such meeting, the lowest whole number that is greater than 40% of the Total Number of Directors; (iii) if the Pre-IPO Owners collectively Beneficially Own at least 30% (but less than 40%) of the total
Outstanding Summit Interests as of the record date for such meeting, the lowest whole number that is greater than 30% of the Total Number of Directors; (iv) if the Pre-IPO Owners collectively Beneficially Own at least 20% (but less than 30%) of
the total Outstanding Summit Interests as of the record date for such meeting, the lowest whole number that is greater than 20% of the Total Number of Directors; and (v) if the Pre-IPO Owners collectively Beneficially Own at least 5% (but less
than 20%) of the total Outstanding Summit Interests as of the record date for such meeting, the lowest whole number that is greater than 10% of the Total Number of Directors. 

(b) If at any time the Blackstone Designator has designated fewer than the total number of individuals that the Blackstone Designator is then
entitled to designate pursuant to Section 2.1(a) hereof, the Blackstone Designator shall have the right to designate such additional individuals which it is entitled to so designate, in which case, any individuals nominated by or at the
direction of the Board or any duly-authorized committee thereof for election as Directors to fill any vacancy on the Board shall include such designees, and the Company shall use its best efforts to (x) effect the election of such additional
designees, whether by increasing the size of the Board or otherwise, and (y) cause the election of such additional designees to fill any such newly-created vacancies or to fill any other existing vacancies. Each such individual whom the
Blackstone Designator shall actually designate pursuant to this Section 2.1 and who is thereafter elected and qualifies to serve as a Director shall be referred to herein as a “Blackstone Designee.” 

(c) In the event that a vacancy is created at any time by the death, disability, retirement or resignation of any Blackstone Designee, any
individual nominated by or at the direction of the Board or any duly-authorized committee thereof to fill such vacancy shall be, and the Company shall use its best efforts to cause such vacancy to be filled, as soon as possible, by a new designee of
the Blackstone Designator, and the Company shall take, to the fullest extent permitted by law, at any time and from time to time, all actions necessary to accomplish the same. 

(d) The Company shall, to the fullest extent permitted by law, include in the slate of nominees recommended by the Board at any meeting of
stockholders called for the purpose of electing directors, the persons designated pursuant to this Section 2.1 and use its best efforts to cause the election of each such designee to the Board, including nominating each such individual
to be elected as a Director as provided herein, recommending such individual’s election and soliciting proxies or consents in favor thereof. 

  
 5 

 (e) In addition to any vote or consent of the Board or the stockholders of the Company required
by applicable Law or the charter or bylaws of the Company, and notwithstanding anything to the contrary in this Agreement, for so long as this Agreement is in effect, any action by the Board to increase or decrease the Total Number of Directors
(other than any increase in the Total Number of Directors in connection with the election of one or more directors elected exclusively by the holders of one or more classes or series of the Company’s stock other than Common Stock) shall require
the prior written consent of the Blackstone Designator, delivered in accordance with Section 5.13 hereof. 
 ARTICLE III. 

INFORMATION; VCOC 
 3.1 Books
and Records; Access. The Company shall, and shall cause its Subsidiaries to, permit the Blackstone Entities and their respective designated representatives, at reasonable times and upon reasonable prior notice to the Company, to review the
books and records of the Company or any of such Subsidiaries and to discuss the affairs, finances and condition of the Company or any of such Subsidiaries with the officers of the Company or any such Subsidiary; provided, however, that
the Company shall not be required to disclose any privileged information of the Company so long as the Company has used commercially reasonable efforts to enter into an arrangement pursuant to which it may provide such information to the Blackstone
Entities without the loss of any such privilege. 
 3.2 Certain Reports. The Company shall deliver or cause to be delivered to
the Blackstone Entities, at their request: 
 (a) to the extent otherwise prepared by the Company, operating and capital expenditure budgets
and periodic information packages relating to the operations and cash flows of the Company and its Subsidiaries; and 
 (b) to the extent
otherwise prepared by the Company, such other reports and information as may be reasonably requested by the Blackstone Entities; provided, however, that the Company shall not be required to disclose any privileged information of the
Company so long as the Company has used commercially reasonable efforts to enter into an arrangement pursuant to which it may provide such information to the Blackstone Entities without the loss of any such privilege. 

3.3 VCOC.
 (a) With
respect to each Blackstone Entity that is intended to qualify its direct or indirect investment in the Company as a “venture capital investment” as defined in the Department of Labor regulations codified at 29 CFR Section 2510.3-101
(the “Plan Asset Regulation”) (each, a “VCOC Investor”), for so long as the VCOC Investor, directly or through one or more subsidiaries, continues to hold any shares of Common Stock (or other securities of the
Company into which such shares of Common Stock may be converted or for which such shares of Common Stock may be exchanged), without limitation or prejudice of any the rights provided to the Blackstone Entities hereunder, the Company shall, with
respect to each such VCOC Investor: 

  
 6 

 (i) provide each VCOC Investor or its designated representative with: 

 

	 	(A)	upon reasonable notice and at mutually convenient times, the right to visit and inspect any of the offices and properties of the Company and its Subsidiaries and inspect and copy the books and records of the Company and
its Subsidiaries; 

  

	 	(B)	as soon as available and in any event within 45 days after the end of each of the first three quarters of each fiscal year of the Company, consolidated balance sheets of the Company and its Subsidiaries as of the end of
such period, and consolidated statements of income and cash flows of the Company and its Subsidiaries for the period then ended prepared in conformity with generally accepted accounting principles in the United States applied on a consistent basis,
except as otherwise noted therein, and subject to the absence of footnotes and to year-end adjustments; 

  

	 	(C)	as soon as available and in any event within 120 days after the end of each fiscal year of the Company, a consolidated balance sheet of the Company and its Subsidiaries as of the end of such year, and consolidated
statements of income and cash flows of the Company and its Subsidiaries for the year then ended prepared in conformity with generally accepted accounting principles in the United States applied on a consistent basis, except as otherwise noted
therein, together with an auditor’s report thereon of a firm of established national reputation; 

  

	 	(D)	to the extent the Company is required by law or pursuant to the terms of any outstanding indebtedness of the Company to prepare such reports, any annual reports, quarterly reports and other periodic reports pursuant to
Section 13 or 15(d) of the Exchange Act, actually prepared by the Company as soon as available; and 

  

	 	(E)	upon written request by the VCOC Investor, copies of all materials provided to the Board, subject to appropriate protections with respect to confidentiality and preservation of attorney-client privilege;

 provided that, in each case, if the Company makes the information described in clauses (B),
(C) and (D) of this Section 3.3(a)(i) available through public filings on the EDGAR System or any successor or replacement system of the U.S. Securities and Exchange Commission, the requirement to deliver such
information shall be deemed satisfied; 

  
 7 

 (ii) make appropriate officers and/or Directors of the Company available, and
cause the officers and directors of its Subsidiaries to be made available, periodically and at such times as reasonably requested by each VCOC Investor, upon reasonable notice and at mutually convenient times, for consultation with such VCOC
Investor or its designated representative with respect to matters relating to the business and affairs of the Company and its Subsidiaries; 

(iii) to the extent that the VCOC Investor requests to receive such information and rights, and to the extent consistent with
applicable Law or listing standards (and with respect to events which require public disclosure, only following the Company’s public disclosure thereof through applicable securities law filings or otherwise), inform each VCOC Investor or its
designated representative in advance with respect to any significant corporate actions, and to provide (or cause to be provided) each VCOC Investor or its designated representative with the right to consult with the Company and its Subsidiaries with
respect to such actions should the VCOC Investor elect to do so; provided, however, that this right to consult must be exercised within five (5) days after the Company informs the VCOC Investor of the proposed corporate action;
provided, further, that the Company shall be under no obligation to provide the VCOC Investor with any material non-public information with respect to such corporate action; and 

(iv) provide each VCOC Investor or its designated representative with such other rights of consultation which the VCOC
Investor’s counsel may determine in writing to be reasonably necessary under applicable legal authorities promulgated after the date hereof to qualify its investment in the Company as a “venture capital investment” for purposes of the
Plan Asset Regulation; provided that the parties agree that any such rights of consultation shall be of a nature consistent with those granted above and nothing in this Agreement shall be deemed to require the Company to grant to the VCOC
Investor any additional rights with respect to the governance or management of the Company. 
 (b) The Company agrees to consider, in good
faith, the recommendations of each VCOC Investor or its designated representative in connection with the matters on which it is consulted as described above in this Section 3.3, recognizing that the ultimate discretion with respect to
all such matters shall be retained by the Company. 
 (c) In the event a VCOC Investor or any of its Affiliates Transfers all or any portion
of their investment in the Company to an Affiliated entity that is intended to qualify as a “venture capital operating company” (as defined in the Plan Asset Regulation), such Transferee shall be afforded the same rights with respect to
the Company afforded to the VCOC Investor hereunder and shall be treated, for such purposes, as a third party beneficiary hereunder. 

  
 8 

 (d) In the event that the Company ceases to qualify as an “operating company” (as
defined in the first sentence of 2510.3-101(c)(1) of the Plan Asset Regulation), or the investment in the Company by a VCOC Investor does not qualify as a “venture capital investment” as defined in the Plan Asset Regulation, then the
Company and each Blackstone Entity will cooperate in good faith to take all reasonable actions necessary, subject to applicable Law, to preserve the VCOC status of each VCOC Investor or the qualification of the investment as a “venture capital
investment,” it being understood that such reasonable actions shall not require a VCOC Investor to purchase or sell any investments. 

(e) For so long as the VCOC Investor, directly or through one or more subsidiaries, continues to hold any shares of Common Stock (or other
securities of the Company into which such shares of Common Stock may be converted or for which such shares of Common Stock may be exchanged) and upon the written request of such VCOC Investor, without limitation or prejudice of any the rights
provided to the Blackstone Entities hereunder, the Company shall, with respect to each such VCOC Investor, furnish and deliver, and in its capacity as the general partner of Summit Holdings, cause Summit Holdings to furnish and deliver, a letter
covering the matters set forth in Sections 3.3(a), 3.3(b), 3.3(c) and 3.3(d) hereof in a form and substance satisfactory to such VCOC Investor. 

ARTICLE IV. 
 ADDITIONAL COVENANTS

 4.1 Pledges. Upon the request of any Blackstone Entity that wishes to pledge, hypothecate or grant security interests in any
or all of the shares of Common Stock or LP Units held by it, including to banks or financial institutions as collateral or security for loans, advances or extensions of credit, the Company agrees to cooperate with each such Blackstone Entity in
taking action reasonably necessary to consummate any such pledge, hypothecation or grant, including without limitation, delivery of letter agreements to lenders in form and substance reasonably satisfactory to such lenders (which may include
agreements by the Company in respect of the exercise of remedies by such lenders) and instructing the transfer agent to transfer any such shares of Common Stock subject to the pledge, hypothecation or grant into the facilities of The Depository
Trust Company without restricted legends. 
 4.2 Post-Closing Date Mergers. The Company agrees that each Blocker Investor Party
shall be entitled to implement either of the following transactions upon the request of the applicable Blocker Investor Party, provided the applicable Blocker Investor Party and the Company have each determined that such transaction would qualify as
a “reorganization” within the meaning of Section 368 of the Internal Revenue Code: (a) the holders of interests of such Blocker Investor Party (or any successor to such Blocker Investor Party) shall contribute (including by way
of a “reverse subsidiary merger”) all of their interests in such Blocker Investor Party to the Company, in exchange for an aggregate number of shares of Class A Common Stock equal to the number of LP Units held by such Blocker
Investor Party along with any rights to which such holders of interests are entitled to under the Tax Receivable Agreement following such contribution, or (b) the Blocker Investor Party (or any successor) shall merge with and into the Company
(or at the Company’s election, a limited liability company wholly owned by the Company that is treated as an entity disregarded as separate and apart from the Company for U.S. federal income tax purposes (a “DRE”)) with the Company or
DRE surviving, as the case may be (the “Surviving Company”), with the holders of interests in such Blocker Investor Party receiving (in the aggregate) a number of shares of Class A Common Stock equal to the number of LP Units
held by such Blocker Investor Party immediately prior to the merger along with any rights to which such holders of interests are entitled to under the Tax Receivable Agreement following such merger. Immediately prior to the consummation of any
contribution or merger described in the preceding sentence, the Blocker Investor Party merging or having its interests contributed (as applicable) (a) shall hold (or be entitled to receive under Summit Holdings LP Agreement) an amount of cash
sufficient (as estimated in the good faith discretion of such Blocker Investor Party and taking into account any losses or 

  
 9 

 
other Tax attributes) to pay all Taxes of the Blocker Investor Party for any Tax period (or portion thereof) ending on or prior to the effective date of such contribution or merger and (b)(i)
shall represent in writing to the Company that it has no liabilities or obligations of any kind whatsoever, whether accrued, contingent, absolute, determined, determinable or otherwise (“Liabilities”), other than Taxes referred to in
clause (a) (to the extent of the cash held by such Blocker Investor Party), or (ii) shall make provisions reasonably acceptable to the Company to arrange for indemnification of the Company for any such Liabilities. The Company agrees to
execute all documents, issue all necessary shares of Class A Common Stock and take all other actions to permit the foregoing transactions to be consummated at the request of each Blocker Investor Party. 

ARTICLE V. 
 GENERAL PROVISIONS

 5.1 Termination. Except for Section 3.3 and Section 4.2 hereof, this Agreement shall terminate on the
earlier to occur of (i) such time as the Blackstone Designator is no longer entitled to designate a Director pursuant to Section 2.1(a) hereof and (ii) the delivery of a written notice by the Blackstone Designator to the
Company requesting that this Agreement terminate. The VCOC Investors shall advise the Company when they collectively first cease to beneficially own any shares of Common Stock (or other securities of the Company into which such shares of Common
Stock may be converted or for which such shares of Common Stock may be exchanged), whereupon Section 3.3 hereof shall terminate. 

5.2 Notices. Any notice, designation, request, request for consent or consent provided for in this Agreement shall be in writing
and shall be either personally delivered, or mailed first class mail (postage prepaid) or sent by reputable overnight courier service (charges prepaid) to the Company at the address set forth below and to any other recipient at the address indicated
on the Company’s records, or at such address or to the attention of such other Person as the recipient party has specified by prior written notice to the sending party. Notices and other such documents will be deemed to have been given or made
hereunder when sent by facsimile (receipt confirmed) delivered personally, five (5) days after deposit in the U.S. mail and one (1) day after deposit with a reputable overnight courier service. 

The Company’s address is: 

Summit Materials, Inc. 
 1550
Wynkoop, 3rd Floor 
 Denver, Colorado 80202 

Attention: Chief Legal Officer 

Fax: (303) 893-6993 
 with a
copy (not constituting notice) to: 
 Simpson Thacher & Bartlett LLP 

425 Lexington Avenue 
 New York,
New York 10017 
 Attention: Edward P. Tolley III and Edgar J. Lewandowski 

Fax: (212) 455-2502 
 The
Blackstone Entities’ address is: 
 The Blackstone Group L.P. 

345 Park Avenue 
 New York, New
York 10154 
 Attention: Neil P. Simpkins 

Fax: [            ] 

  
 10 

 with a copy (not constituting notice) to: 

Simpson Thacher & Bartlett LLP 

425 Lexington Avenue 
 New York,
New York 10017 
 Attention: Edward P. Tolley III and Edgar J. Lewandowski 

Fax: (212) 455-2502 
 5.3
Amendment; Waiver. This Agreement may be amended, supplemented or otherwise modified only by a written instrument executed by the Company and the other parties hereto. Neither the failure nor delay on the part of any party hereto to
exercise any right, remedy, power or privilege under this Agreement shall operate as a waiver thereof, nor shall any single or partial exercise of any right, remedy, power or privilege preclude any other or further exercise of the same or of any
other right, remedy, power or privilege, nor shall any waiver of any right, remedy, power or privilege with respect to any occurrence be construed as a waiver of such right, remedy, power or privilege with respect to any other occurrence. No waiver
shall be effective unless it is in writing and is signed by the party asserted to have granted such waiver. 
 5.4 Further
Assurances. The parties hereto will sign such further documents, cause such meetings to be held, resolutions passed, exercise their votes and do and perform and cause to be done such further acts and things necessary, proper or advisable in
order to give full effect to this Agreement and every provision hereof. To the fullest extent permitted by law, the Company shall not directly or indirectly take any action that is intended to, or would reasonably be expected to result in,
Blackstone or any Blackstone Entity being deprived of the rights contemplated by this Agreement. 
 5.5 Assignment. This
Agreement will inure to the benefit of and be binding on the parties hereto and their respective successors and permitted assigns. This Agreement may not be assigned without the express prior written consent of the other parties hereto, and any
attempted assignment, without such consents, will be null and void; provided, however, that, without the prior written consent of the Company, a Blackstone Party may assign this Agreement, in whole or in part, to any of its
Permitted Assigns. 
 5.6 Third Parties. Except as provided for in Article II, Section 3.3,
Section 4.1 with respect to any Blackstone Entity and Section 4.2 with respect to each Blocker Investor Party, this Agreement does not create any rights, claims or benefits inuring to any person that is not a party hereto nor create or
establish any third party beneficiary hereto. 
 5.7 Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of Delaware, without regard to principles of conflicts of laws thereof. 

  
 11 

 5.8 Jurisdiction; Waiver of Jury Trial. In any judicial proceeding involving any
dispute, controversy or claim arising out of or relating to this Agreement, each of the parties unconditionally accepts the jurisdiction and venue of the courts of the State of Delaware or if jurisdiction over the matter is vested exclusively in
federal courts, the United States District Court for the District of Delaware, and the appellate courts to which orders and judgments thereof may be appealed. In any such judicial proceeding, the parties agree that in addition to any method for the
service of process permitted or required by such courts, to the fullest extent permitted by law, service of process may be made by delivery provided pursuant to the directions in Section 5.2 hereof. EACH OF THE PARTIES HEREBY WAIVES TO
THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW TRIAL BY JURY IN ANY JUDICIAL PROCEEDING INVOLVING ANY DISPUTE, CONTROVERSY OR CLAIM ARISING OUT OF OR RELATING TO THIS AGREEMENT. 

5.9 Specific Performance. Each party hereto acknowledges and agrees that in the event of any breach of this Agreement by any of
them, the other parties hereto would be irreparably harmed and could not be made whole by monetary damages. Each party accordingly agrees to waive the defense in any action for specific performance that a remedy at law would be adequate and agrees
that the parties, in addition to any other remedy to which they may be entitled at law or in equity, shall be entitled to specific performance of this Agreement without the posting of bond. 

5.10 Entire Agreement. This Agreement sets forth the entire understanding of the parties hereto with respect to the subject matter
hereof. There are no agreements, representations, warranties, covenants or understandings with respect to the subject matter hereof or thereof other than those expressly set forth herein and therein. This Agreement supersedes all other prior
agreements and understandings between the parties with respect to such subject matter. 
 5.11 Severability. If any provision of this
Agreement, or the application of such provision to any Person or circumstance or in any jurisdiction, shall be held to be invalid or unenforceable to any extent, (i) the remainder of this Agreement shall not be affected thereby, and each other
provision hereof shall be valid and enforceable to the fullest extent permitted by law, (ii) as to such Person or circumstance or in such jurisdiction such provision shall be reformed to be valid and enforceable to the fullest extent permitted
by law, and (iii) the application of such provision to other Persons or circumstances or in other jurisdictions shall not be affected thereby. 

5.12 Table of Contents, Headings and Captions. The table of contents, headings, subheadings and captions contained in this
Agreement are included for convenience of reference only, and in no way define, limit or describe the scope of this Agreement or the intent of any provision hereof. 

5.13 Grant of Consent. Any vote, consent or approval of, or designation by, or other action of, the Blackstone Designator
hereunder shall be effective if notice of such vote, consent, approval, designation or action is provided in accordance with Section 5.2 hereof by the Blackstone Party or Parties holding of record a majority of the Outstanding Summit
Interests then held of record by Blackstone Parties as of the latest date any such notice is so provided. 

  
 12 

 5.14 Counterparts. This Agreement and any amendment hereto may be signed in any
number of separate counterparts, each of which shall be deemed an original, but all of which taken together shall constitute one Agreement (or amendment, as applicable). 

5.15 Effectiveness. This Agreement shall become effective upon the Closing Date. 

5.16 No Recourse. This Agreement may only be enforced against, and any claims or cause of action that may be based upon, arise out
of or relate to this Agreement, or the negotiation, execution or performance of this Agreement may only be made against the entities that are expressly identified as parties hereto and no past, present or future Affiliate, director, officer,
employee, incorporator, member, manager, partner, stockholder, agent, attorney or representative of any party hereto shall have any liability for any obligations or liabilities of the parties to this Agreement or for any claim based on, in respect
of, or by reason of, the transactions contemplated hereby. 
 [Remainder of Page Intentionally Left Blank] 

  
 13 

 IN WITNESS WHEREOF, the parties hereto have executed this Agreement on the day and year first
above written. 
  

			
	 COMPANY

	
	 SUMMIT MATERIALS, INC.

		
	 By:
	 	  

	 Name:

	 Title:

  
 [Signature Page to
Summit Materials, Inc. Stockholders’ Agreement] 

 
			
	 BLACKSTONE PARTIES:

	
	 [SIGNATURE BLOCKS TO COME]

  

  
 [Signature Page to
Summit Materials, Inc. Stockholders’ Agreement]

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