X0306 4 2018-02-27 0 0001621563 Summit Materials, Inc. SUM 0001440948 Hill Thomas W. C/O SUMMIT MATERIALS, INC. 1550 WYNKOOP STREET, 3RD FLOOR DENVER CO 80202 1 1 0 0 President & CEO Class A Common Stock 2018-02-27 4 S 0 6300 32.04 D 152846 D Class A Common Stock 2018-02-28 4 S 0 6200 32.02 D 146646 D Class A Common Stock 2018-02-28 4 M 0 10253 A 156899 D Class A Common Stock 2018-02-28 4 F 0 2497 31.63 D 154402 D Class A Common Stock 365 I See Footnote Restricted Stock Units 2018-02-28 4 M 0 10253 0 D Class A Common Stock 10253 20504 D Restricted Stock Units 2018-02-28 4 A 0 51757 0 A Class A Common Stock 51757 51757 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $31.77 to $32.51, 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. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $31.62 to $32.33, 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. Reflects restricted stock units that upon vesting converted into shares of Class A common stock of the Issuer ("Class A Common Stock") on a one-for-one basis. Reflects securities held by a trust for the benefit of Mr. Hill's family, for which Mr. Hill's spouse serves as trustee. Each restricted stock unit represents a contingent right to receive one share of Issuer Class A Common Stock. The restricted stock units will be settled in either Class A Common Stock or cash (or a combination thereof) at the discretion of the Issuer's compensation committee. On February 28, 2017, the Reporting Person was granted 30,757 restricted stock units that vest in three equal annual installments beginning on February 28, 2018. These restricted stock units vest in three equal annual installments beginning on February 28, 2019. The Reporting Person disclaims beneficial ownership of the securities reported herein as indirectly beneficially owned, except to the extent of his pecuniary interest therein. /s/Anne Lee Benedict, as Attorney-in-Fact 2018-03-01