X0306 4 2016-05-16 0 0001621563 Summit Materials, Inc. SUM 0001636106 Rauh Douglas Charles C/O SUMMIT MATERIALS, INC. 1550 WYNKOOP STREET, 3RD FLOOR DENVER CO 80202 0 1 0 0 See Remarks Class A Common Stock 2016-05-16 4 C 0 10000 A 13552 D Class A Common Stock 2016-05-16 4 S 0 10000 21.60 D 3552 D LP Units of Summit Materials Holdings L.P. 2016-05-16 4 C 0 10000 D Class A Common Stock 10000 187077 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 on a one-for-one basis. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $21.55 to $21.66, inclusive. The reporting person undertakes to provide to the issuer, any security holder of the issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth above. Title: EVP and Chief Operating Officer /s/Anne Lee Benedict, as Attorney-in-Fact 2016-05-18