X0306 4 2020-02-28 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 2020-02-28 4 M 0 10252 A 177446 D Class A Common Stock 2020-02-28 4 M 0 17252 A 194698 D Class A Common Stock 2020-02-28 4 M 0 35179 A 229877 D Class A Common Stock 2020-02-28 4 A 0 20829 0 A 250706 D Class A Common Stock 2020-02-28 4 F 0 20314 19.54 D 230392 D Class A Common Stock 365 I See Footnote Restricted Stock Units 2020-02-28 4 M 0 10252 0 D Class A Common Stock 10252 0 D Restricted Stock Units 2020-02-28 4 M 0 17252 0 D Class A Common Stock 17252 17253 D Restricted Stock Units 2020-02-28 4 M 0 35179 0 D Class A Common Stock 35179 70358 D Restricted Stock Units 2020-02-28 4 A 0 69231 0 A Class A Common Stock 69231 69231 D 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 shares of Class A Common Stock earned and delivered on performance units previously granted based upon the satisfaction of certain performance criteria. 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. On February 28, 2018, the Reporting Person was granted 51,757 restricted stock units that vest in three equal annual installments beginning on February 28, 2019. On February 28, 2019, the Reporting Person was granted 105,537 restricted stock units that vest in three equal annual installments beginning on February 28, 2020. These restricted stock units vest in three equal annual installments beginning on February 28, 2021. 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 2020-03-03