X0306 4 2023-02-22 0 0001621563 Summit Materials, Inc. SUM 0001667708 Cooney Anne M C/O SUMMIT MATERIALS, INC 1801 CALIFORNIA STREET, SUITE 3500 DENVER CO 80202 1 0 0 0 Restricted Stock Units 2023-02-22 4 A 0 4038 0 A Class A Common Stock 4038.0 4038 D Each restricted stock unit represents a contingent right to receive one share of Class A common stock of the 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 Human Capital and Compensation Committee. These restricted stock units vest on February 28, 2024. The Reporting Person has elected to defer settlement of these restricted stock units to a date following the vesting date pursuant to the terms of the Reporting Person's deferral election. /s/ Christopher B. Gaskill, as Attorney-in-Fact 2023-02-24