Document:

EX-10.4

 Exhibit 10.4 

REGISTRATION RIGHTS AGREEMENT 

This Registration Rights Agreement (as amended, restated, supplemented or otherwise modified from time to time, this
“Agreement”) is dated as of March 17, 2015, and is between Summit Materials, Inc., a Delaware corporation (the “Company”) and the Blackstone Holders (as defined below), the Continental Holders (as
defined below) and the other holders of Registrable Securities (as defined below) party hereto. Such holders of Registrable Securities party hereto are collectively referred to herein as the “Securityholders.” 

ARTICLE I 
 DEFINITIONS

 In this Agreement: 

“Affiliate” has the meaning ascribed thereto in Rule 12b-2 promulgated under the Exchange Act, as in effect on the date
hereof. 
 “Agreement” has the meaning set forth in the preamble. 

“Blackstone” means the entities comprising the Blackstone Holders, their respective Affiliates and the
successors and permitted assigns of the entities and their respective Affiliates. 
 “Blackstone Demand
Notice” has the meaning set forth in Section 2.2(a) hereof. 
 “Blackstone
Holders” means the entities listed on the signature pages hereto under the heading “Blackstone Holders.” 

“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 common 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 common stock is reclassified or reconstituted. 

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

“Continental Demand Notice” has the meaning set forth in Section 2.2(b) hereof. 

“Continental Holders” means the entities listed on the signature pages hereto under the heading
“Continental Holders.” 

 “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. 
 “Demand
Notice” means each of a Blackstone Demand Notice or a Continental Demand Notice. 
 “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 as of or about the date hereof, among the Company, the
Partnership and holders of LP Units from time to time party thereto, as amended from time to time. 
 “Exchange
Registration” has the meaning ascribed to such term in Section 2.1(a) hereof. 

“FINRA” means the Financial Industry Regulatory Authority, Inc. 

“IPO” means an underwritten registered public offering of the Company’s Class A Common Stock in
connection with which the Class A Common Stock first becomes listed on a Recognized Exchange. 
 “LP
Units” has the meaning given to such term in the Exchange Agreement. 
 “Partnership”
means Summit Materials Holdings L.P., a Delaware limited partnership. 
 “Partnership Agreement” means the
Fourth Amended and Restated Limited Partnership Agreement of Summit Materials Holdings L.P., dated as of March 11, 2015, as amended, restated, supplemented or modified, from time to time. 

“Person” means an individual, a partnership, a corporation, a limited liability company, an association, a
joint stock company, a trust, a joint venture, a cooperative, 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. 
 “Recognized Exchange” means The New York Stock Exchange or the
Nasdaq National Market. 
 “Registrable Securities” means shares of Class A Common Stock that may be
delivered in exchange for LP Units and other shares of Class A Common Stock otherwise held by Securityholders from time to time. For purposes of this Agreement, Registrable Securities shall cease to be Registrable Securities when (i) a
registration statement covering resales of such 

  
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Registrable Securities has been declared effective under the Securities Act by the SEC and such Registrable Securities have been disposed of pursuant to such effective registration statement,
(ii) such Registrable Securities are eligible to be sold by Securityholders owning such Registrable Securities (including Registrable Securities deliverable to a Securityholder under an effective Exchange Registration) pursuant to Rule 144 or
145 (or any similar provision then in effect) under the Securities Act, without limitation thereunder on volume or manner of sale, unless such Registrable Securities are held by a Holder that beneficially own Shares representing 5% or more of the
aggregate voting power of shares of Class A Common Stock and Class B Common Stock eligible to vote in the election of directors of the Company or (iii) such Registrable Securities cease to be outstanding (or issuable upon exchange). 

“Registration Expenses” means any and all expenses incurred in connection with the performance of or compliance
with this Agreement, including: 
 (a) all SEC, stock exchange, or FINRA registration and filing fees (including, if applicable, the fees and
expenses of any “qualified independent underwriter,” as such term is defined in Rule 5121 of FINRA, and of its counsel); 
 (b) all
fees and expenses of complying with securities or blue sky laws (including fees and disbursements of counsel for the underwriters in connection with blue sky qualifications of the Registrable Securities); 

(c) all printing, messenger and delivery expenses; 

(d) all fees and expenses incurred in connection with the listing of the Registrable Securities on any securities exchange or FINRA and all
rating agency fees; 
 (e) the reasonable fees and disbursements of counsel for the Company and of its independent public accountants,
including the expenses of any special audits and/or “cold comfort” letters required by or incident to such performance and compliance; 

(f) any fees and disbursements of underwriters customarily paid by the issuers or sellers of Securities, including liability insurance if the
Company so desires or if the underwriters so require, and the reasonable fees and expenses of any special experts retained in connection with the requested registration, but excluding underwriting discounts and commissions and transfer taxes, if
any; 
 (g) the reasonable fees and out-of-pocket expenses of not more than one law firm (as selected by Blackstone, if it is participating
in such registration, and otherwise, by Securityholders of a majority of the Registrable Securities included in such registration) incurred by all the Securityholders in connection with the registration; 

(h) the costs and expenses of the Company relating to analyst and investor presentations or any “road show” undertaken in connection
with the registration and/or marketing of the Registrable Securities (including the reasonable out-of-pocket expenses of the Securityholders); and 

(i) any other fees and disbursements customarily paid by the issuers of Securities. 

  
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 “SEC” means the U.S. Securities and Exchange Commission or any
successor agency. 
 “Shares” means shares of Class A Common Stock of the Company. Shares held by or on behalf
of a Securityholder the certificate for which does not bear a Securities Act restrictive legend, which Shares may be resold freely without registration under the Securities Act, will not be considered Shares for purposes of the demand and piggyback
provisions of this Agreement. 
 “Securities” means capital stock, limited partnership interests, limited
liability company interests, beneficial interests, warrants, options, notes, bonds, debentures, and other securities, equity interests, ownership interests and similar obligations of every kind and nature of any Person. 

“Securities Act” means the Securities Act of 1933, as amended, and the rules and regulations promulgated
thereunder, as the same may be amended from time to time. 
 “Securityholders” has the meaning set forth in
the preamble. 
 “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 any 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 director or
general partner of such limited liability company, partnership, association or other business entity. 

“WKSI” means a well-known seasoned issuer, as defined in Rule 405 under the Securities Act. 

ARTICLE II 
 DEMAND AND
PIGGYBACK RIGHTS 
 2.1 Exchange Registration. 

(a) The Company shall use its commercially reasonable efforts to file with the SEC prior to the time that LP Units held by Securityholders
other than Blackstone become available for exchange for Class A Common Stock pursuant to the terms of the Exchange Agreement and cause to be declared effective under the Securities Act by the SEC promptly

  
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thereafter, one or more registration statements (the “Exchange Registration”) covering the delivery by the Company from time to time to Securityholders other than
Blackstone of all shares of Class A Common Stock deliverable to such Securityholders in exchange for LP Units pursuant to the Exchange Agreement. 

(b) The Company shall be liable for and pay all Registration Expenses in connection with any Exchange Registration, regardless of whether such
registration is effected. 
 2.2 Right to Demand a Non-Shelf Registered Offering; Continental Demand Rights.

 (a) Upon the written demand of Blackstone made at any time and from time to time (a “Blackstone Demand
Notice”), the Company will facilitate in the manner described in this Agreement a non-shelf registered offering of the Registrable Securities requested by Blackstone to be included in such offering. 

(b) Upon the written demand of one or more of the Continental Holders made at any time following the third anniversary of the consummation of
the Company’s IPO (a “Continental Demand Notice”), the Company will facilitate in the manner described in this Agreement either (i) a non-shelf registered offering of the Registrable Securities requested by
the Continental Holders to be included in such offering, or (ii) an underwritten “takedown” of Registrable Securities off of an effective shelf registration statement, as applicable; provided that (i) the market value,
based on the closing price of the Company’s Class A Common Stock on the Business Day immediately preceding the date of the Continental Demand Notice, of the aggregate amount of Registrable Securities held by the Continental Holders that
are requested in such Demand Notice to be included in such registered offering or underwritten takedown, as applicable, is at least $40,000,000 and (ii) the Continental Holders shall be entitled to only one such registration/takedown. 

(c) Any demanded non-shelf registered offering may, at the Company’s option, include Shares to be sold by the Company for its own account
and will also, other than in connection with the Company’s IPO, include Registrable Securities to be sold by Securityholders that exercise their related piggyback rights pursuant to Section 2.3 hereof and any other Registrable
Securities to be sold by the holders of registration rights granted other than pursuant to this Agreement exercising such rights, in each case, to the extent exercising such rights on a timely basis. In order to be valid, the Demand Notice must
provide the information described in Section 3.1 hereof (if applicable) and Section 4.5 hereof or be followed by such information, when requested as contemplated by Section 4.5 hereof. 

(d) Without limiting any other obligations of the Company hereunder, as soon as reasonably practicable, but in no event later than 60 days
after receiving a valid Demand Notice satisfying the criteria set forth in Section 2.2 hereof, the Company shall file with the SEC a registration statement covering all of the Registrable Securities covered by such Demand Notice as well
as any other Registrable Securities as to which registration is properly requested in accordance with Section 2.3 hereof (which other Registrable Securities may be included by means of a pre-effective amendment) and any other registrable
securities properly requested in accordance with other registration rights agreements with the Company, but subject in each case to any cutbacks imposed in accordance with Section 3.5 hereof and the limitations set forth in
Section 2.7 hereof. 

  
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 2.3 Right to Piggyback on a Non-Shelf Registered Offering. After the
Company’s IPO, in connection with any registered offering of Shares covered by a non-shelf registration statement (whether pursuant to the exercise of demand rights or at the initiative of the Company), the Securityholders may exercise
piggyback rights to have included in such offering Registrable Securities held by them, subject in each case to any cutbacks imposed in accordance with Section 3.5 hereof and the limitations set forth in Section 2.7 hereof;
provided that the Continental Holders shall only be entitled to exercise such piggyback rights in connection with any registered underwritten offering in which Blackstone participates. The Company will facilitate in the manner described in
this Agreement any such non-shelf registered offering. 
 2.4 Right to Demand and be Included in a Shelf
Registration. Upon the demand of Blackstone, made at any time and from time to time when the Company is eligible to utilize Form S-3 or a successor form to sell Shares in a secondary offering on a delayed or continuous basis in
accordance with Rule 415 under the Securities Act, the Company will facilitate in the manner described in this Agreement a shelf registration of Registrable Securities held by the Securityholders. Any shelf registration filed pursuant to this
Section 2.4 by the Company covering Shares (whether pursuant to a demand by Blackstone or at the initiative of the Company) will cover Registrable Securities held by each of the Securityholders (regardless of whether they demanded the
filing of such shelf or not) equal to the percentage of their original respective holdings as is requested by Blackstone with respect to the Registrable Securities of Blackstone to be included in such shelf. If at the time of such request the
Company is a WKSI, such shelf registration shall, upon the approval of the board of directors of the Company, cover an unspecified number of Registrable Securities to be sold by the Company and its Securityholders. 

2.5 Demand and Piggyback Rights for Shelf Takedowns. Upon the demand of (A) Blackstone, made at any time and
from time to time, or (B) the Continental Holders, in accordance with Section 2.2(b) hereof, the Company will facilitate in the manner described in this Agreement a “takedown” of Registrable Securities off of an effective
shelf registration statement. In connection with any underwritten shelf takedown (whether pursuant to the exercise of such demand rights by Blackstone or the Continental Holders, as applicable, or at the initiative of the Company), the
Securityholders may exercise piggyback rights to have included in such takedown Registrable Securities held by them that are registered on such shelf; provided that the Continental Holders shall only be entitled to exercise such piggyback
rights in connection with any underwritten shelf takedown in which Blackstone participates. 
 2.6 Right to Reload a
Shelf. Upon the approval of the board of directors of the Company, the Company will file and seek the effectiveness of a post-effective amendment to an existing shelf in order to register up to the number of Registrable
Securities previously taken down off of such shelf by all Securityholders and not yet “reloaded” onto such shelf. The board of directors of the Company (or certain designated members thereof) will consult and coordinate with Blackstone in
order to accomplish such replenishments from time to time in a sensible manner. 

  
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 2.7 Limitations on Demand and Piggyback Rights. 

(a) Any demand for the filing of a registration statement or for a registered offering or takedown, and the exercise of any piggyback
registration rights, will be subject to the constraints of any applicable lockup arrangements, and any such demand must be deferred until such lockup arrangements no longer apply. If a demand has been made for a non-shelf registered offering or for
an underwritten takedown, no further demands may be made so long as the related offering is still being pursued. Notwithstanding anything in this Agreement to the contrary, the Securityholders will not have piggyback or other registration rights
with respect to the following registered primary offerings by the Company: (i) a registration relating solely to employee benefit plans; (ii) a registration on Form S-4 or S-8 (or other similar successor forms then in effect under the
Securities Act); (iii) a registration pursuant to which the Company is offering to exchange its own Securities for other Securities; (iv) a registration statement relating solely to dividend reinvestment or similar plans; (v) a shelf
registration statement pursuant to which only the initial purchasers and subsequent transferees of debt securities of the Company or any Subsidiary that are convertible for Interests or Common Stock and that are initially issued pursuant to Rule
144A and/or Regulation S of the Securities Act may resell such notes and sell the common equity into which such notes may be converted; (vi) a registration where the Registrable Securities are not being sold for cash or (vii) an Exchange
Registration. 
 (b) The Company may postpone the filing of a demanded registration statement (other than in connection with the
Company’s IPO) or suspend the effectiveness of any shelf registration statement for a reasonable “blackout period” not in excess of 90 days if the board of directors of the Company determines in good faith that such registration or
offering could materially interfere with a bona fide business, acquisition or divestiture or financing transaction of the Company or is reasonably likely to require premature disclosure of information, the premature disclosure of which could
materially and adversely affect the Company; provided that the Company shall not delay the filing of any demanded registration statement more than once in any 12-month period. The blackout period will end upon the earlier to occur of,
(i) in the case of a bona fide business, acquisition or divestiture or financing transaction, a date not later than 90 days from the date such deferral commenced, and (ii) in the case of disclosure of non-public information, the
earlier to occur of (x) the filing by the Company of its next succeeding Form 10-K or Form 10-Q, or (y) the date upon which such information is otherwise disclosed. 

ARTICLE III 
 NOTICES,
CUTBACKS AND OTHER MATTERS 
 3.1 Notifications Regarding Registration Statements. In order for
Blackstone or the Continental Holders, as applicable, to exercise their right to demand that a registration statement be filed, they must include in their Demand Notice the number of Registrable Securities sought to be registered and the proposed
plan of distribution. 

  
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 3.2 Notifications Regarding Registration Piggyback Rights. 

(a) In the event that the Company receives (i) any demand from Blackstone or the Continental Holders, as applicable, pursuant to
Section 2.2 hereof, or (ii) if the Company files a registration statement with respect to a non-shelf registered offering, the Company will promptly give to each of the Securityholders a written notice thereof no later than 5:00
p.m., New York City time, on the fifth Business Day following receipt by the Company of such demand or the filing of such registration statement, as applicable. Any Securityholder wishing to exercise its piggyback rights with respect to any such
non-shelf registration statement must notify the Company and the other Securityholders of the number of Registrable Securities it seeks to have included in such registration statement in a written notice. Such notice must be given as soon as
practicable, but in no event later than 5:00 p.m., New York City time, on the second Business Day prior to (i) if applicable, the date on which the preliminary prospectus intended to be used in connection with pre-effective marketing efforts
for the relevant offering is expected to be finalized, and (ii) in any case, the date on which the pricing of the relevant offering is expected to occur. No such notice is required in connection with a shelf registration statement, as
Registrable Securities held by all Securityholders will be included up to the applicable percentage. 
 (b) Pending any required public
disclosure and subject to applicable legal requirements, the parties will maintain appropriate confidentiality of their discussions regarding a prospective non-shelf registration. 

3.3 Notifications Regarding Demanded Underwritten Takedowns. 

(a) The Company will keep the Securityholders reasonably apprised of all pertinent aspects of any underwritten shelf takedown demanded by
Blackstone or the Continental Holders, as applicable, in order that Securityholders may have a reasonable opportunity to exercise their related piggyback rights. Without limiting the Company’s obligation as described in the preceding sentence,
having a reasonable opportunity requires that the Securityholders be notified by the Company of an anticipated underwritten takedown (whether pursuant to a demand made by Blackstone or the Continental Holders, as applicable, or made at the
Company’s own initiative) no later than 5:00 p.m., New York City time, on (i) if applicable, the second Business Day prior to the date on which the preliminary prospectus or prospectus supplement intended to be used in connection with
pre-pricing marketing efforts for such takedown is finalized, and (ii) in all cases, the second Business Day prior to the date on which the pricing of the relevant takedown occurs. 

(b) Any Securityholder wishing to exercise its piggyback rights with respect to an underwritten shelf takedown must notify the Company and the
other Securityholders of the number of Registrable Securities it seeks to have included in such takedown. Such notice must be given as soon as practicable, but in no event later than 5:00 p.m., New York City time, on (i) if applicable, the
Business Day prior to the date on which the preliminary prospectus or prospectus supplement intended to be used in connection with marketing efforts for the relevant offering is expected to be finalized, and (ii) in all cases, the Business Day
prior to the date on which the pricing of the relevant takedown occurs. 

  
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 (c) Pending any required public disclosure and subject to applicable legal requirements, the
parties will maintain appropriate confidentiality of their discussions regarding a prospective underwritten takedown. 
 3.4
Plan of Distribution, Underwriters, Advisors and Counsel. If a majority of the Registrable Securities proposed to be sold in an underwritten offering through a non-shelf registration statement or through a shelf takedown is
being sold by the Company for its own account, the Company will be entitled to determine the plan of distribution and select the managing underwriters and any provider of advisory services, which may include Affiliates of Blackstone, for such
offering. Otherwise, Blackstone, if participating in such offering (or Securityholders holding a majority of the Shares requested to be included if Blackstone is not participating in such offering), will be entitled to determine the plan of
distribution and select the managing underwriters and any provider of advisory services, which may include Affiliates of Blackstone; provided that such investment banker or bankers, managers and providers of advisory services shall be
reasonably satisfactory to the Company), and will also be entitled to select counsel for the selling Securityholders (which may be the same as counsel for the Company). 

3.5 Cutbacks. If the managing underwriters advise the Company and the selling Securityholders that, in their
opinion, the number of Registrable Securities requested to be included in an underwritten offering exceeds the amount that can be sold in such offering without adversely affecting the distribution of the Registrable Securities being offered, the
price that will be paid in such offering or the marketability thereof, such offering will include only the number of Registrable Securities that the underwriters advise can be sold in such offering. If the Company is selling Registrable Securities
for its own account in such offering and the offering is not being made on account of a demand made by Blackstone or the Continental Holders, as applicable, pursuant to Section 2.2 hereof, the Company will have first priority. To the
extent of any remaining capacity, and in all other cases, the selling Securityholders (and any other Persons having registration rights pari passu with the Securityholders and participating in such offering) and the Company will be subject to
cutback pro rata based on the number of Registrable Securities initially requested by them to be included in such offering, without distinguishing between Securityholders (or other Persons exercising pari passu registration rights)
based on who made the demand for such offering or otherwise. 
 3.6 Withdrawals. Even if Registrable
Securities held by a Securityholder have been part of a registered underwritten offering, such Securityholder may, no later than the time at which the public offering price and underwriters’ discount are determined with the managing
underwriter, decline to sell all or any portion of the Registrable Securities being offered for its account. 
 3.7
Lockups. In connection with any underwritten offering of Shares, the Company and each Securityholder will agree (in the case of Securityholders, with respect to Registrable Securities respectively held by them) to be bound by
the underwriting agreement’s lockup restrictions (which must apply in like manner to all of them) that are agreed to by the Company. In addition, the Securityholders shall be bound by their obligations with respect to any lockup arrangements or
other restrictions on transfer of Registrable Securities set forth in the Partnership Agreement. 

  
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 ARTICLE IV 

FACILITATING REGISTRATIONS AND OFFERINGS 

4.1 General. If the Company becomes obligated under this Agreement to facilitate a registration and offering of
Registrable Securities on behalf of Securityholders, the Company will do so with the same degree of care and dispatch as would reasonably be expected in the case of a registration and offering by the Company of Registrable Securities for its own
account. Without limiting this general obligation, the Company will fulfill its specific obligations as described in this Article IV. 

4.2 Registration Statements. In connection with each registration statement that is demanded by Securityholders in
accordance with this Agreement or as to which piggyback rights otherwise apply, the Company will: 
 (a) (1) prepare and file with the
SEC a registration statement on an appropriate form covering the applicable Registrable Securities, (2) file amendments thereto as warranted, (3) seek the effectiveness thereof, and (4) file with the SEC prospectuses and prospectus
supplements as may be required, all in consultation with Blackstone and as reasonably necessary in order to permit the offer and sale of the such Registrable Securities in accordance with the applicable plan of distribution; 

(b) (1) within a reasonable time prior to the filing of any registration statement, any prospectus, any amendment to a registration
statement, amendment or supplement to a prospectus or any free writing prospectus (in each case including all exhibits filed therewith), provide copies of such documents to the selling Securityholders and to the underwriter or underwriters of an
underwritten offering, if applicable, and to their respective counsel; fairly consider such reasonable changes in any such documents prior to or after the filing thereof as the counsel to the Securityholders or the underwriter or the underwriters
may request; and make such of the representatives of the Company as shall be reasonably requested by the selling Securityholders or any underwriter available for discussion of such documents; and (2) within a reasonable time prior to the
filing of any document which is to be incorporated by reference into a registration statement or a prospectus, provide copies of such document to counsel for the Securityholders and underwriters; fairly consider such reasonable changes in such
document prior to or after the filing thereof as counsel for such Securityholders or such underwriter shall request; and make such of the representatives of the Company as shall be reasonably requested by such counsel available for discussion of
such document; 
 (c) use all reasonable efforts to cause each registration statement and the related prospectus and any amendment or
supplement thereto, as of the effective date of such registration statement, amendment or supplement and during the distribution of the registered Registrable Securities (x) to comply in all material respects with the requirements of the
Securities Act (including the rules and regulations promulgated thereunder) and (y) not to contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements
therein not misleading; 

  
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 (d) notify each Securityholder promptly, and, if requested by such Securityholder, confirm such
advice in writing, (i) when a registration statement has become effective and when any post-effective amendments and supplements thereto become effective if such registration statement or post-effective amendment is not automatically effective
upon filing pursuant to Rule 462 under the Securities Act, (ii) of the issuance by the SEC or any state securities authority of any stop order, injunction or other order or requirement suspending the effectiveness of a registration statement or
the initiation of any proceedings for that purpose, (iii) if, between the effective date of a registration statement and the closing of any sale of securities covered thereby pursuant to any agreement to which the Company is a party, the
representations and warranties of the Company contained in such agreement cease to be true and correct in all material respects or if the Company receives any notification with respect to the suspension of the qualification of the Registrable
Securities for sale in any jurisdiction or the initiation of any proceeding for such purpose, and (iv) of the happening of any event during the period a registration statement is effective as a result of which such registration statement or the
related prospectus contains any untrue statement of a material fact or omits to state any material fact required to be stated therein or necessary to make the statements therein not misleading; 

(e) furnish counsel for each underwriter, if any, and for the Securityholders copies of any correspondence with the SEC or any state securities
authority relating to the registration statement or prospectus; 
 (f) otherwise use all reasonable efforts to comply with all applicable
rules and regulations of the SEC, including making available to its security holders an earnings statement covering at least 12 months which shall satisfy the provisions of Section 11(a) of the Securities Act and Rule 158 thereunder (or any
similar provision then in force); and 
 (g) use all reasonable efforts to obtain the withdrawal of any order suspending the effectiveness of
a registration statement at the earliest possible time. 
 4.3 Non-Shelf Registered Offerings and Shelf
Takedowns. In connection with any non-shelf registered offering or shelf takedown that is demanded by Securityholders or as to which piggyback rights otherwise apply, the Company will: 

(a) cooperate with the selling Securityholders and the sole underwriter or managing underwriter of an underwritten offering, if any, to
facilitate the timely preparation and delivery of certificates representing the Registrable Securities to be sold and not bearing any restrictive legends; and enable such Registrable Securities to be in such denominations (consistent with the
provisions of the governing documents thereof) and registered in such names as the selling Securityholders or the sole underwriter or managing underwriter of an underwritten offering of Registrable Securities, if any, may reasonably request at least
five days prior to any sale of such Registrable Securities; 
 (b) furnish to each Securityholder and to each underwriter, if any,
participating in the relevant offering, without charge, as many copies of the applicable prospectus, including each preliminary prospectus, and any amendment or supplement thereto and such other documents as such Securityholder or underwriter may
reasonably request in order to facilitate the public sale or other disposition of the Registrable Securities; the Company hereby consents to the use of the prospectus, including each preliminary prospectus, by each such Securityholder and
underwriter in connection with the offering and sale of the Registrable Securities covered by the prospectus or the preliminary prospectus; 

  
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 (c) (1) use all reasonable efforts to register or qualify the Registrable Securities being
offered and sold, no later than the time the applicable registration statement becomes effective, under all applicable state securities or blue sky laws of such jurisdictions as each underwriter, if any, or any Securityholder holding Registrable
Securities covered by a registration statement, shall reasonably request; (2) use all reasonable efforts to keep each such registration or qualification effective during the period such registration statement is required to be kept
effective; and (3) do any and all other acts and things which may be reasonably necessary or advisable to enable each such underwriter, if any, and Securityholder to consummate the disposition in each such jurisdiction of such Registrable
Securities owned by such Securityholder; provided, however, that the Company shall not be obligated to qualify as a foreign corporation or as a dealer in securities in any jurisdiction in which it is not so qualified or to consent to
be subject to general service of process (other than service of process in connection with such registration or qualification or any sale of Registrable Securities in connection therewith) in any such jurisdiction; 

(d) cause all Registrable Securities being sold to be qualified for inclusion in or listed on any Recognized Exchange on which Registrable
Securities issued by the Company are then so qualified or listed if so requested by the Securityholders, or if so requested by the underwriter or underwriters of an underwritten offering of Registrable Securities, if any; 

(e) cooperate and assist in any filings required to be made with FINRA and in the performance of any due diligence investigation by any
underwriter in an underwritten offering; 
 (f) use all reasonable efforts to facilitate the distribution and sale of any Registrable
Securities to be offered pursuant to this Agreement, including without limitation by making “road show” presentations, holding meetings with and making calls to potential investors and taking such other actions as shall be requested by the
Securityholders or the lead managing underwriter of an underwritten offering; 
 (g) in the case of an offering that includes a provider of
advisory services, enter into and perform its obligations under customary agreements (including an advisory services agreement and an indemnification agreement in customary form); and 

(h) enter into customary agreements (including, in the case of an underwritten offering, underwriting agreements in customary form, and
including provisions with respect to indemnification and contribution in customary form and consistent with the provisions relating to indemnification and contribution contained herein) and take all other customary and appropriate actions in order
to expedite or facilitate the disposition of such Registrable Securities and in connection therewith: 

  
 12 

 (1) make such representations and warranties to the selling Securityholders and the underwriters,
if any, in form, substance and scope as are customarily made by issuers to underwriters in similar underwritten offerings; 
 (2) obtain
opinions of counsel to the Company and updates thereof (which counsel and opinions (in form, scope and substance) shall be reasonably satisfactory to the lead managing underwriter, if any) addressed to each selling Securityholder and the
underwriters, if any, covering the matters customarily covered in opinions requested in sales of securities or underwritten offerings and such other matters as may be reasonably requested by such Securityholders and underwriters; 

(3) obtain “cold comfort” letters and updates thereof from the Company’s independent certified public accountants addressed to
the selling Securityholders, if permissible, and the underwriters, if any, which letters shall be customary in form and shall cover matters of the type customarily covered in “cold comfort” letters to underwriters in connection with
primary underwritten offerings; and 
 (4) to the extent requested and customary for the relevant transaction, enter into a Securities sales
agreement with the Securityholders providing for, among other things, the appointment of such representative as agent for the selling Securityholders for the purpose of soliciting purchases of Registrable Securities, which agreement shall be
customary in form, substance and scope and shall contain customary representations, warranties and covenants; and 
 The above shall be done at such times
as customarily occur in similar registered offerings or shelf takedowns. 
 4.4 Due Diligence. In connection
with each registration and offering of Registrable Securities to be sold by Securityholders, the Company will, in accordance with customary practice, make available for inspection by representatives of the Securityholders and underwriters and any
counsel or accountant retained by such Securityholders or underwriters all relevant financial and other records, pertinent corporate documents and properties of the Company and cause appropriate officers, managers, employees, outside counsel and
accountants of the Company to supply all information reasonably requested by any such representative, underwriter, counsel or accountant in connection with their due diligence exercise, including through in-person meetings, but subject to customary
privilege constraints. 
 4.5 Information from Securityholders. Each Securityholder that holds Registrable Securities
covered by any registration statement will furnish to the Company such information regarding itself as is required to be included in the registration statement or is otherwise required by FINRA or the SEC in connection with such registration
statement, the ownership of Registrable Securities by such Securityholder and the proposed distribution by such Securityholder of such Registrable Securities as the Company may from time to time reasonably request in writing. 

4.6 Expenses. All Registration Expenses incurred in connection with any registration statement or registered
offering covering Registrable Securities held by the Securityholders will be borne by the Company. However, underwriters’, brokers’ and dealers’ discounts and commissions applicable to Registrable Securities sold for the account of a
Securityholder will be borne by such Securityholder. 

  
 13 

 ARTICLE V 

INDEMNIFICATION 
 5.1
Indemnification by the Company. In the event of any registration under the Securities Act by any registration statement pursuant to rights granted in this Agreement of Registrable Securities held by Securityholders, the
Company will indemnify and hold harmless Securityholders, their officers, directors and affiliates, and each underwriter of such securities and each other Person, if any, who Controls any Securityholder or such underwriter within the meaning of the
Securities Act, against any losses, claims, damages, or liabilities (including legal fees and costs of court), joint or several, to which Securityholders or such underwriter or controlling Person may become subject under the Securities Act or
otherwise, including any amount paid in settlement of any litigation commenced or threatened, and shall promptly reimburse such Persons, as and when incurred, for any legal or other expenses reasonably incurred by them in connection with
investigating any claims and defending any actions, insofar as such losses, claims, damages, or liabilities (or any actions in respect thereof) arise out of or are based upon any violation or alleged violation by the Company of the Securities Act,
any blue sky laws, securities laws or other applicable laws of any state or country in which such Shares are offered and relating to action taken or action or inaction required of the Company in connection with such offering, or arise out of or are
based upon any untrue statement or alleged untrue statement of any material fact (i) contained, on its effective date, in any registration statement under which such securities were registered under the Securities Act or any amendment or
supplement to any of the foregoing, or which arise out of or are based upon the omission or alleged omission to state a material fact required to be stated therein or necessary to make the statements therein not misleading or (ii) contained in
any preliminary prospectus, if used prior to the effective date of such registration statement, or in the final prospectus (as amended or supplemented if the Company shall have filed with the SEC any amendment or supplement to the final prospectus),
or which arise out of or are based upon the omission or alleged omission to state a material fact required to be stated in such prospectus or necessary to make the statements in such prospectus not misleading; and will reimburse Securityholders and
each such underwriter and each such controlling Person for any legal or any other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage, or liability; provided, however, that
the Company shall not be liable to any Securityholder or its underwriters or controlling Persons in any such case to the extent that any such loss, claim, damage, or liability arises out of or is based upon an untrue statement or alleged untrue
statement or omission or alleged omission made in such registration statement or such amendment or supplement, in reliance upon and in conformity with information furnished to the Company through a written instrument duly executed by Securityholders
or such underwriter specifically for use in the preparation thereof. 
 5.2 Indemnification by Securityholders.
Each Securityholder as a condition to including Registrable Securities in such registration statement will indemnify and hold harmless (in the same manner and to the same extent as set forth in Section 5.1 hereof) the Company, each
director of the Company, each officer of the Company who shall sign the 

  
 14 

 
registration statement, and any Person who Controls the Company within the meaning of the Securities Act, (i) with respect to any statement or omission from such registration statement, or
any amendment or supplement to it, if such statement or omission was made in reliance upon and in conformity with information furnished to the Company through a written instrument duly executed by such Securityholder specifically regarding such
Securityholder for use in the preparation of such registration statement or amendment or supplement, and (ii) with respect to compliance by such Securityholder with applicable laws in effecting the sale or other disposition of the securities
covered by such registration statement. 
 5.3 Indemnification Procedures. Promptly after receipt by an indemnified party
of notice of the commencement of any action involving a claim referred to in Section 5.1 and Section 5.2 hereof, the indemnified party will, if a claim in respect thereof is to be made or may be made against an indemnifying
party, give written notice to such indemnifying party of the commencement of the action. The failure of any indemnified party to give notice shall not relieve the indemnifying party of its obligations in this Article V, except to the extent
that the indemnifying party is actually prejudiced by the failure to give notice. If any such action is brought against an indemnified party, the indemnifying party will be entitled to participate in and to assume the defense of the action with
counsel reasonably satisfactory to the indemnified party, and after notice from the indemnifying party to such indemnified party of its election to assume defense of the action, the indemnifying party will not be liable to such indemnified party for
any legal or other expenses incurred by the latter in connection with the action’s defense other than reasonable costs of investigation. An indemnified party shall have the right to employ separate counsel in any action or proceeding and
participate in the defense thereof, but the fees and expenses of such counsel shall be at such indemnified party’s expense unless (i) the employment of such counsel has been specifically authorized in writing by the indemnifying party,
which authorization shall not be unreasonably withheld, (ii) the indemnifying party has not assumed the defense and employed counsel reasonably satisfactory to the indemnified party within thirty (30) days after notice of any such action
or proceeding, or (iii) the named parties to any such action or proceeding (including any impleaded parties) include the indemnified party and the indemnifying party and the indemnified party shall have been advised by such counsel that there
may be one or more legal defenses available to the indemnified party that are different from or additional to those available to the indemnifying party (in which case the indemnifying party shall not have the right to assume the defense of such
action or proceeding on behalf of the indemnified party), it being understood, however, that the indemnifying party shall not, in connection with any one such action or separate but substantially similar or related actions in the same jurisdiction
arising out of the same general allegations or circumstances, be liable for the reasonable fees and expenses of more than one separate firm of attorneys (in addition to all local counsel which is necessary, in the good faith opinion of both counsel
for the indemnifying party and counsel for the indemnified party in order to adequately represent the indemnified parties) for the indemnified party and that all such fees and expenses shall be reimbursed as they are incurred upon written request
and presentation of invoices. Whether or not a defense is assumed by the indemnifying party, the indemnifying party will not be subject to any liability for any settlement made without its consent (not to be unreasonably withheld). No indemnifying
party will consent to entry of any judgment or enter into any settlement which (i) does not include as an unconditional term the giving by the claimant or plaintiff, to the indemnified party, of a release from all liability in respect of such
claim or litigation or (ii) involves the imposition of equitable remedies or the imposition of any non-financial obligations on the indemnified party. 

  
 15 

 5.4 Contribution. If the indemnification required by this Article V
from the indemnifying party is unavailable to or insufficient to hold harmless an indemnified party in respect of any indemnifiable losses, claims, damages, liabilities, or expenses, then the indemnifying party shall contribute to the amount paid or
payable by the indemnified party as a result of such losses, claims, damages, liabilities, or expenses in such proportion as is appropriate to reflect (i) the relative benefit of the indemnifying and indemnified parties and (ii) if the
allocation in clause (i) is not permitted by applicable law, in such proportion as is appropriate to reflect the relative benefit referred to in clause (i) and also the relative fault of the indemnified and indemnifying parties, in
connection with the actions which resulted in such losses, claims, damages, liabilities, or expenses, as well as any other relevant equitable considerations. The relative benefits received by a party shall be deemed to be in the same proportion as
the total net proceeds from the offering (before deducting expenses) received by it bear to the total amounts (including, in the case of any underwriter, any underwriting commissions and discounts) received by each other party. The relative fault of
the indemnifying party and the indemnified party shall be determined by reference to, among other things, whether any action in question, including any untrue or alleged untrue statement of a material fact, has been made by, or relates to
information supplied by, such indemnifying party or parties, and the parties’ relative intent, knowledge, access to information, and opportunity to correct or prevent such action. The amount paid or payable by a party as a result of the losses,
claims, damage, liabilities, and expenses referred to above shall be deemed to include any legal or other fees or expenses reasonably incurred by such party in connection with any investigation or proceeding. The Company and Securityholders agree
that it would not be just and equitable if contribution pursuant to this Section 5.4 were determined by pro rata allocation or by any other method of allocation which does not take account of the equitable
considerations referred to in the prior provisions of this Section 5.4. 
 Notwithstanding the provisions of this
Section 5.4, no indemnifying party shall be required to contribute any amount in excess of the amount by which the total price at which the securities were offered to the public by such indemnifying party exceeds the amount of any
damages which such indemnifying party has otherwise been required to pay by reason of an untrue statement or omission. No Person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be
entitled to contribution from any Person who was not guilty of such a fraudulent misrepresentation. 
 ARTICLE VI  

OTHER AGREEMENTS 
 6.1
Assignment. Neither the Company nor any Securityholder shall assign all or any part of this Agreement without the prior written consent of the Company and Blackstone; provided, however, that without the prior written
consent of the Company, Blackstone may assign its rights and obligations under this Agreement in whole or in part to (x) any of its Affiliates and/or (y) any Person who becomes a holder of Registrable Securities upon a distribution by
Blackstone of shares of Class A Common Stock or LP Units to its members, limited partners or stockholders that becomes a party hereto by executing and delivering an assignment and joinder agreement to the Company, substantially in the form of
Exhibit A to this Agreement. Except as otherwise provided herein, this Agreement will inure to the benefit of and be binding on the parties hereto and their respective successors and permitted assigns. 

  
 16 

 6.2 Merger or Consolidation. In the event the Company engages in a merger or
consolidation in which the Registrable Securities are converted into securities of another company, appropriate arrangements will be made so that the registration rights provided under this Agreement continue to be provided to Securityholders by the
issuer of such securities. To the extent such new issuer, or any other company acquired by the Company in a merger or consolidation, was bound by registration rights obligations that would conflict with the provisions of this Agreement, the Company
will, unless Securityholders then holding at least 90% of the Registrable Securities otherwise agree, use its commercially reasonable efforts to modify any such “inherited” registration rights obligations so as not to interfere in any
material respects with the rights provided under this Agreement. To the extent any such modification of “inherited” registration rights disproportionately and adversely impacts any Securityholder hereunder, such modification shall not be
effective as to such Securityholder without the consent of such Securityholder. 
 6.3 Limited Liability. Notwithstanding
any other provision of this Agreement, neither the members, general partners, limited partners or managing directors, or any directors or officers of any members, general or limited partner, advisory director, nor any future members, general
partners, limited partners, advisory directors, or managing directors, if any, of any Securityholder shall have any personal liability for performance of any obligation of such Securityholder under this Agreement in excess of the respective capital
contributions of such members, general partners, limited partners, advisory directors or managing directors to such Securityholder. 

6.4 Rule 144. If the Company is subject to the requirements of Section 13, 14 or 15(d) of the Exchange Act, the
Company covenants that it will file any reports required to be filed by it under the Securities Act and the Exchange Act (or, if the Company is subject to the requirements of Section 13, 14 or 15(d) of the Exchange Act but is not required to
file such reports, it will, upon the request of any Securityholder, make publicly available such information) and it will take such further action as any Securityholder may reasonably request, so as to enable such Securityholder to sell Registrable
Securities without registration under the Securities Act within the limitation of the exemptions provided by (a) Rule 144 under the Securities Act, as such Rule may be amended from time to time, or (b) any similar rule or regulation
hereafter adopted by the SEC. Upon the request of any Securityholder, the Company will deliver to such Securityholder a written statement as to whether it has complied with such requirements. For the avoidance of doubt, this Section 6.4
shall not in any way limit or otherwise modify any applicable restrictions on transfer set forth in the Partnership Agreement. 
 6.5
In-Kind Distributions. If any Securityholder seeks to effectuate an in-kind distribution of all or part of its Registrable Securities to its direct or indirect equityholders, the Company will, subject to applicable lockups, work with
such Securityholder and the Company’s transfer agent to facilitate such in-kind distribution in the manner reasonably requested by such Securityholder. 

  
 17 

 ARTICLE VII 

MISCELLANEOUS 
 7.1
Notices. All notices, requests, demands and other communications required or permitted hereunder shall be made in writing by hand-delivery, registered first-class mail, telex, fax or air courier guaranteeing delivery to the Persons
at the respective addresses set forth below or pursuant to such other instructions as may be designated in writing by the party to receive such notice. 
  

	 	(a)	If to the Company, to: 

 Summit Materials, Inc. 

1550 Wynkoop, 3rd Floor 

Denver, Colorado 80202 

Attention: Chief Legal Officer 

Fax: (303) 893-6993 

E-mail: Legal@summit-materials.com 

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 

E-mail: etolley@stblaw.com and elewandowski@stblaw.com 
  

	 	(b)	If to Blackstone, to: 

 The Blackstone Group L.P. 

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

Fax: (212) 583-5712 
 E-mail:
Simpkins@blackstone.com 
 with a copy (not constituting notice) to: 

Simpson Thacher & Bartlett LLP 

425 Lexington Avenue 
 New York,
New York 10017 
 Attention: Wilson S. Neely 

Fax: (212) 455-2502 

E-mail: wneely@stblaw.com 

  
 18 

	 	(c)	If to the Continental Holders, to: 

 Missouri Materials Company, L.L.C. and J & J
Midwest Group, L.L.C. 
 Midwest Cement Company 

221 Bolivar, Suite 401 

Jefferson City, MO 65101 

Attention: Mike Farmer 
 Fax:
(573) 636-8618 
 E-mail: mfarmer@farmercompanies.com 

R. Michael Johnson Family Limited Liability Company 

R. Michael Johnson Family Limited Liability Company 

146 N. Bemiston 
 Clayton, MO
63105 
 Thomas A. Beck Family, LLC 

Thomas A. Beck Family, LLC 
 1
Forest Hills Ridge Ct. 
 Fax: (636) 532-7445 

with a copy (not constituting notice) to: 

Greensfelder, Hemker & Gale, P.C. 

10 South Broadway, Suite 2000 

St. Louis, MO 63102 
 Attention:
Phillip Stanton 
 Fax: (314) 241-3237 

E-mail: prs@greensfelder.com 

Any such notice, request, demand or other communication shall be deemed to have been duly given (a) on the date of delivery if delivered
personally or by facsimile or electronic transmission, (b) on the first Business Day after being sent if delivered by nationally recognized overnight delivery service and (c) upon the earlier of actual receipt thereof or five Business Days
after the date of deposit in the United States mail if delivered by mail. 
 7.2 Section Headings. The article and
section headings in this Agreement are for reference purposes only and shall not affect the meaning or interpretation of this Agreement. References in this Agreement to a designated “Article” or “Section” refer to an Article or
Section of this Agreement unless otherwise specifically indicated. 
 7.3 Governing Law. This Agreement shall be governed
by, and construed and enforced in accordance with, the laws of the State of New York. 
 7.4 Consent to Jurisdiction and Service
of Process; Waiver of Jury Trial. 
 (a) The parties to this Agreement hereby agree to submit to the jurisdiction of the courts of
the State of New York, the courts of the United States of America for the Southern District of New York, and appellate courts from any thereof in any action or proceeding arising out of or relating to this Agreement. 

(b) EACH OF THE PARTIES HERETO HEREBY IRREVOCABLY WAIVES ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL PROCEEDING ARISING OUT OF OR RELATED
TO THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY. 
 7.5 Amendments. 

                (a) This Agreement may be amended only by an instrument in
writing executed by the Company and Securityholders holding at least a majority of the Registrable Securities collectively held by them; provided that any amendment that would adversely impact the rights hereunder of Blackstone or the
Continental Holders shall require the prior written consent of Blackstone or the Continental Holders holding a majority of the Registrable Securities collectively held by them, as applicable; provided, further, that any amendment that
would disproportionately and adversely impact (i) the rights hereunder of the Securityholders party hereto other than Blackstone without similarly affecting the rights hereunder of Blackstone (other than the granting of demand rights to any new
party to become a Securityholder hereunder and rights incidental thereto) shall require the prior approval of a such Securityholders other than Blackstone holding a majority of the Registrable Securities held by such Securities, (ii) the rights
hereunder of any Securityholder other than Blackstone without similarly affecting the rights hereunder of all other Securityholders other than Blackstone shall require the prior written consent of such Securityholder. This Agreement will terminate
as to any Securityholder when it no longer holds any Registrable Securities. 

  
 19 

 (b) Notwithstanding anything in Section 7.5(a) hereof to the contrary, if the Company
at any time after the date of this Agreement grants to any other holders of its securities (other than any new Blackstone Holders becoming party hereto after the date hereof) any rights to request or cause the Company to effect the registration
under the Securities Act or offering or sale of any such securities on any terms materially more favorable to such holders than the terms set forth in this Agreement, the terms of this Agreement shall, upon the request of Blackstone, be deemed
amended or supplemented to the extent necessary to provide Blackstone such more favorable rights and benefits, and, at the election and sole discretion of Blackstone (as evidenced by a written notice to the Company), shall be deemed amended or
supplemented to the extent necessary to provide to the Securityholders party hereto other than Blackstone those more favorable rights and benefits as selected by Blackstone to be provided to such other Securityholders and set forth in such written
notice. 
 7.6 Entire Agreement. This Agreement contains the entire understanding of the parties with respect to the
subject matter hereof. The registration rights granted under this Agreement supersede any registration, qualification or similar rights with respect to any of the Registrable Securities granted under any other agreement, and any of such preexisting
registration rights are hereby terminated. 
 7.7 Severability. The invalidity or unenforceability of any specific
provision of this Agreement shall not invalidate or render unenforceable any of its other provisions. Any provision of this Agreement held invalid or unenforceable shall be deemed reformed, if practicable, to the extent necessary to render it valid
and enforceable and to the extent permitted by law and consistent with the intent of the parties to this Agreement. 
 7.8
Counterparts. This Agreement may be executed in multiple counterparts, including by means of facsimile, each of which shall be deemed an original, but all of which together shall constitute the same instrument. 

7.9 Additional Holders. Notwithstanding anything herein to the contrary, the Company may from time to time add additional
holders of Registrable Securities of the Company as parties to this Agreement with the consent of Blackstone and without the consent or additional signatures of any other holders of Registrable Securities hereunder. In order to become a party to
this Agreement, such additional party must execute a signature page evidencing such party’s agreement to be bound hereby as a Securityholder (but not Blackstone, unless Blackstone consents in writing thereto), and upon the Company’s
receipt of any such additional holder’s executed signature page hereto, such additional holder shall be deemed to be a party hereto and such additional signature pages shall be a part of this Agreement. 

  
 20 

 7.10 Equitable Remedies. The parties hereto agree that irreparable harm would occur
in the event that any of the agreements and provisions of this Agreement were not performed fully by the parties hereto in accordance with their specific terms or conditions or were otherwise breached, and that money damages are an inadequate remedy
for breach of this Agreement because of the difficulty of ascertaining and quantifying the amount of damage that will be suffered by the parties hereto in the event that this Agreement is not performed in accordance with its terms or conditions or
is otherwise breached. It is accordingly hereby agreed that the parties hereto shall be entitled to an injunction or injunctions to restrain, enjoin and prevent breaches of this Agreement by the other parties and to enforce specifically the terms
and provisions hereof in any court of the United States or any state having jurisdiction, such remedy being in addition to and not in lieu of, any other rights and remedies to which the other parties are entitled to at law or in equity. 

[Remainder of page intentionally left blank] 

  
 21 

 IN WITNESS WHEREOF, the undersigned have executed this Agreement as of the date first written
above. 
  

			
	COMPANY:
	
	SUMMIT MATERIALS, INC.
		
	By:		 /s/ Thomas W. Hill

			Name: Thomas W. Hill
			Title: Chief Executive Officer
	
	BLACKSTONE HOLDERS:

  

			
	BLACKSTONE PARTICIPATION PARTNERSHIP
	(CAYMAN) 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 (CAYMAN) 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

 [Signature Page to Summit Materials Registration Rights Agreement] 

			
	BLACKSTONE CAPITAL PARTNERS (CAYMAN) 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
	
	BLACKSTONE CAPITAL PARTNERS (CAYMAN) 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

 [Signature Page to Summit Materials Registration Rights Agreement] 

			
	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

 [Signature Page to Summit Materials Registration Rights Agreement] 

			
	CONTINENTAL HOLDERS:
	
	MISSOURI MATERIALS COMPANY, L.L.C.
		
	By:		 /s/ Elliot E. Farmer

	Name:		Elliot E. Farmer, Trustee of the Elliot E. Farmer Family Trust, dated May 26, 1999
	Title:		Member
	
	J & J MIDWEST GROUP, L.L.C.
		
	By:		 /s/ Elliot E. Farmer

	Name:		Elliot E. Farmer, Trustee of the Elliot E. Farmer Family Trust, dated May 26, 1999
	Title:		Member
	
	R. MICHAEL JOHNSON FAMILY LIMITED LIABILITY COMPANY
		
	By:		 /s/ R. Michael Johnson

	Name:		R. Michael Johnson
	Title:		Managing Member
	
	THOMAS A. BECK FAMILY, LLC
		
	By:		 /s/ Thomas A. Beck

	Name:		Thomas A. Beck
	Title:		Member

  
 [Signature Page to Summit
Materials Registration Rights Agreement] 

			
	OTHER SECURITYHOLDERS:
	
	All other Securityholders listed in Annex 1 attached hereto
		
	By:		 /s/ Anne Lee Benedict

	Name:		Anne Lee Benedict
	Title:		Attorney-in-Fact

  
 [Signature Page to Summit
Materials Registration Rights Agreement] 

 Annex 1 

Silverhawk Summit, L.P. 

 Exhibit A 

FORM OF ASSIGNMENT AND JOINDER 

[            ], 20     

Reference is made to the Registration Rights Agreement, dated as of March 17, 2015, by and among Summit Materials, Inc. (the
“Company”), the Blackstone Holders (as defined therein) and the other parties thereto (the “Registration Rights Agreement”). Capitalized terms used but not otherwise defined herein shall have the
meanings ascribed to such terms in the Registration Rights Agreement. 
 Pursuant to Section 6.1 of the Registration Rights
Agreement, [            ] (the “Assignor”) in its capacity as a Blackstone Holder in the Registration Rights Agreement hereby assigns [in part][or: in full]
its rights and obligations under the Registration Rights Agreement to each of [            ], [            ] and
[            ] (each, an “Assignee” and collectively, the “Assignees”). [For the avoidance of doubt, the Assignor will remain a party to the
Registration Rights Agreement following the assignment in part of its rights and obligations thereunder to the undersigned Assignees.] 

Each undersigned Assignee hereby agrees to and does become party to the Registration Rights Agreement as a Blackstone Holder and
Securityholder. This assignment and joinder shall serve as a counterpart signature page to the Registration Rights Agreement and by executing below each undersigned Assignee is deemed to have executed the Registration Rights Agreement with the same
force and effect as if originally named a party thereto and each Assignee’s shares of Class A Common Stock shall be included as Registrable Securities under the Registration Rights Agreement. 

[Remainder of Page Intentionally Left Blank.] 

 IN WITNESS WHEREOF, the undersigned have duly executed this assignment and joinder as of date
first set forth above. 
  

			
	ASSIGNOR:
	
	[            ]
		
	By:		  

			Name:
			Title:
	
	ASSIGNEE(S):
	
	[            ]
		
	By:		  

			Name:
			Title:EX-10.5

 Exhibit 10.5 

STOCKHOLDERS’ AGREEMENT 

DATED AS OF MARCH 11, 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 March 11, 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 March 11, 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: (212) 583-5712 

  
 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:
		 /s/ Thomas W. Hill

	 Name: Thomas W. Hill

	 Title:   Chief Executive Officer

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

 
			
	 BLACKSTONE PARTIES:

	
	BLACKSTONE PARTICIPATION PARTNERSHIP (CAYMAN) 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 (CAYMAN) 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

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

			
	BLACKSTONE CAPITAL PARTNERS (CAYMAN) 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
	
	BLACKSTONE CAPITAL PARTNERS (CAYMAN) 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

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

			
	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

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

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