X0306 4 2017-05-04 0 0001621563 Summit Materials, Inc. SUM 0001228680 GARDNER TED A C/O SUMMIT MATERIALS, INC. 1550 WYNKOOP STREET, 3RD FLOOR DENVER CO 80202 1 0 0 0 Class A Common Stock 2017-05-04 4 M 0 57555 18 A 57555 I See Footnote Class A Common Stock 2017-05-04 4 F 0 36211 28.61 D 21344 I See Footnote Class A Common Stock 2017-05-05 4 S 0 21344 28.04 D 0 I See Footnote Class A Common Stock 6414 D Warrants 18 2017-05-04 4 M 0 57555 0 D 2025-03-11 Class A Common Stock 57555 0 I See Footnote Warrants 18 2025-03-11 Class A Common Stock 27408 27408 I See Footnote Reflects securities held by certain investment funds affiliated with Silverhawk Summit, L.P. ("Silverhawk"). Mr. Gardner, a managing partner and co-founder of Silverhawk, may be deemed to have beneficial ownership of the securities of the Issuer held by Silverhawk. On May 4, 2017, the Reporting Person exercised warrants to purchase 57,555 shares of Class A Common Stock for $18.00 per share. The Reporting Person paid the exercise price on a cashless basis, resulting in the Issuer withholding 36,211 of the warrant shares to pay the exercise price and issuing to the Reporting Person the remaining 21,344 shares. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $28.03 to $28.07, 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. These warrants are fully exercisable. Reflects securities held by a limited liability company controlled by Mr. Gardner. 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 2017-05-08