X0306 4 2019-02-15 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 2019-02-15 4 P 0 31250 16.25 A 135652 D Class A Common Stock 365 I See Footnote The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions ranging from $16.00 to $16.25, 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 purchased at each separate price within the range set forth above. Reflects securities held by a trust for the benefit of Mr. Hill's family, for which Mr. Hill's spouse serves as trustee. 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 2019-02-19