Exhibit 10.2

AMENDMENT NO. 1 TO STOCKHOLDERS’ AGREEMENT

This AMENDMENT NO. 1 TO STOCKHOLDERS’ AGREEMENT, dated as of July 16, 2015 (this
“Amendment”), is entered into by and between Summit Materials, Inc., a Delaware
corporation (the “Company”) and each of the other parties identified on the
signature pages hereto (the “Investor Parties”). This Amendment is an amendment
to the Stockholders’ Agreement, dated as of March 11, 2015 (the “Agreement”) by
and between the Company and the Investor Parties.

RECITALS:

WHEREAS, the Company and the Investor Parties desire to amend the Agreement with
respect to the matters set forth herein.

NOW THEREFORE, in consideration of the premises and agreements hereinafter set
forth, the parties hereto hereby agree as follows:

Section 1. Amendments. The Agreement is hereby amended to amend and restate the
definition of “Outstanding Summit Interests” in its entirety to reach as
follows:

“Outstanding Summit Interests” means the aggregate number of votes all
outstanding shares of Common Stock would at such time be entitled to vote
generally in the election of Directors. 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 votes
such Person is entitled to as a holder of Class B Common Stock, assuming in each
case that the LP Units held by such Person have been exchanged for Class A
Common Stock in accordance with the Exchange Agreement.

Section 2. Status. This Amendment amends the Agreement, but only to the extent
expressly set forth herein. All other provisions of the Agreement remain in full
force and effect. Unless otherwise defined herein, initially capitalized terms
have the meaning given them in the Agreement.

Section 3. Governing Law. This Amendment shall be governed by and construed in
accordance with the applicable terms and provisions of Section 5.7 of the
Agreement, which terms and provisions are incorporated herein by reference.

Section 4. Counterparts. This Amendment may be executed in one or more
counterparts, each of which shall be deemed to be an original, but all of which
shall be considered one and the same instrument.

Section 5. Facsimile Execution. Facsimile signatures on counterparts of this
Amendment are hereby authorized and shall be acknowledged as if such facsimile
signatures were an original execution, and this Amendment shall be deemed as
executed when an executed facsimile hereof is transmitted by a party to any
other party.

[Remainder of Page Intentionally Left Blank]

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IN WITNESS WHEREOF, each of the parties hereto has executed this Amendment as of
the date first written above.

 

COMPANY SUMMIT MATERIALS, INC. By:  

/s/ Thomas W. Hill

Name:   Thomas W. Hill Title:   Chief Executive Officer

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INVESTOR PARTIES: BLACKSTONE PARTICIPATION PARTNERSHIP (DELAWARE) V-NQ L.P. By:
  BCP V-NQ GP L.L.C., its U.S. general partner By:  

/s/ Neil P. Simpkins

Name:   Neil P. Simpkins Title:   Senior Managing Director BLACKSTONE FAMILY
INVESTMENT PARTNERSHIP (DELAWARE) V-NQ L.P. By:   BCP V-NQ GP L.L.C., its U.S.
general partner By:  

/s/ Neil P. Simpkins

Name:   Neil P. Simpkins Title:   Senior Managing Director BLACKSTONE CAPITAL
PARTNERS (DELAWARE) V-NQ L.P. By:   Blackstone Management Associates (Cayman)
V-NQ L.P., its general partner By:   BCP V-NQ GP L.L.C., its U.S. general
partner By:  

/s/ Neil P. Simpkins

Name:   Neil P. Simpkins Title:   Senior Managing Director

 

[Amendment No.1 to Stockholders’ Agreement]

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BLACKSTONE CAPITAL PARTNERS (DELAWARE) NQ V-AC L.P. By:   Blackstone Management
Associates (Cayman) V-NQ L.P., its general partner By:   BCP V-NQ GP L.L.C., its
U.S. general partner By:  

/s/ Neil P. Simpkins

Name:   Neil P. Simpkins Title:   Senior Managing Director SUMMIT BCP
INTERMEDIATE HOLDINGS L.P. By:   Summit BCP Intermediate Holdings GP, Ltd., its
general partner By:  

/s/ Neil P. Simpkins

Name:   Neil P. Simpkins Title:   Director

 

[Amendment No.1 to Stockholders’ Agreement]