As filed with the Securities and Exchange Commission on August 5, 2015.

Registration No. 333-                     

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Summit Materials, Inc.

(Exact Name of Registrant as Specified in its Charter)

1550 Wynkoop Street, 3rd Floor

Denver, Colorado 80202

(303) 893-0012

(Address, including zip code, and telephone number, including area code, of Registrant’s principal executive offices)

Anne Lee Benedict, Esq.

Chief Legal Officer

Summit Materials, Inc.

1550 Wynkoop Street, 3rd Floor

Denver, Colorado 80202

(303) 893-0012

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Approximate date of commencement of the proposed sale of the securities to the public: As soon as practicable after the Registration Statement is declared effective.

If any of the securities being registered on this form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box.    ¨

If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    x  File No. 333-205561

If this form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    ¨

If this form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

CALCULATION OF REGISTRATION FEE

This Registration Statement shall become effective upon filing with the Securities and Exchange Commission in accordance with Rule 462(b) promulgated under the Securities Act.

EXPLANATORY NOTE AND INCORPORATION OF

CERTAIN INFORMATION BY REFERENCE

This Registration Statement on Form S-1 is being filed with the Securities and Exchange Commission (the “Commission”) pursuant to Rule 462(b) under the Securities Act of 1933, as amended, by Summit Materials, Inc. (the “Registrant”). This Registration Statement incorporates by reference the contents of, including all exhibits to, the Registrant’s Registration Statement on Form S-1 (File No. 333-205561), as amended, which was declared effective by the Commission on August 5, 2015.

The Registrant hereby (i) undertakes to pay the Commission the filing fee set forth on the cover page of this Registration Statement by a wire transfer of such amount as soon as practicable (but no later than the close of business on August 6, 2015) and (ii) certifies that it has sufficient funds in the relevant account to cover the amount of such filing fee.

SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Denver, State of Colorado, on August 5, 2015.

Pursuant to the requirements of the Securities Act of 1933, as amended, this registration statement has been signed by the following persons in the capacities indicated on the 5th day of August, 2015.