X0306 4 2016-07-19 0 0001621563 Summit Materials, Inc. SUM 0001636107 Evans Mikel Shane C/O SUMMIT MATERIALS, INC. 1550 WYNKOOP STREET, 3RD FLOOR DENVER CO 80202 0 1 0 0 See Remarks Class A Common Stock 2016-07-19 4 C 0 39400 A 45490 D Class A Common Stock 2016-07-19 4 S 0 39400 20.67 D 6090 D LP Units of Summit Materials Holdings L.P. 2016-07-19 4 C 0 39400 D Class A Common Stock 39400 218525 D Pursuant to the terms of an exchange agreement, dated as of March 11, 2015, the limited partnership units of Summit Materials Holdings L.P. ("LP Units") reported herein are exchangeable from and after the first anniversary of the closing of the issuer's initial public offering (subject to the terms of the exchange agreement and vesting requirements, including certain vesting events more fully described in the issuer's Registration Statement on Form S-1 (File No. 333-201058)) for shares of the issuer's Class A common stock ("Class A Common Stock") on a one-for-one basis. This amount represents the $20.75 public offering price per share of Class A Common Stock, less the underwriting discount of $0.08 per share. Title: EVP & West Division President /s/ Anne Lee Benedict, as Attorney-in-Fact 2016-07-21