X0306 4 2015-03-11 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 LP Units of Summit Materials Holdings L.P. 2015-03-11 4 A 0 252726 A Class A Common Stock 252726 252726 I See Footnote LP Units of Summit Materials Holdings L.P. 2015-03-11 4 A 0 3091203 A Class A Common Stock 3091203 3091203 I See Footnote Warrants 18.00 2015-03-11 4 A 0 27408 A 2025-03-11 Class A Common Stock 27408 27408 I See Footnote Warrants 18.00 2015-03-11 4 A 0 57555 A 2025-03-11 Class A Common Stock 57555 57555 I See Footnote LP Units of Summit Materials Holdings L.P. 2015-08-11 4 D 0 957951 D Class A Common Stock 957951 253499 I See Footnote Pursuant to the terms of an exchange agreement, dated as of March 11, 2015, the limited partnership units of Summit Materials Holdings L.P. ("LP Units") reported herein are exchangeable from and after the first anniversary of the closing of the issuer's initial public offering (subject to the terms of the exchange agreement and vesting requirements, including certain vesting events more fully described in the issuer's Registration Statement on Form S-1 (File No. 333-201058) (the "Registration Statement")) for shares of the issuer's Class A common stock on a one-for-one basis. These securities were acquired in connection with the reclassification of the interests of Summit Material Holdings L.P. prior to the issuer's initial public offering (as more fully described in the Registration Statement). Reflects securities held by a limited liability company controlled by Mr. Gardner. 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. The warrants are exercisable beginning on the first anniversary of the closing of the issuer's initial public offering. Silverhawk sold to the issuer the number of LP Units set forth above at a price per LP Unit of $24.784375, which represents the $25.75 price at which the issuer's Class A common stock was sold in a secondary offering, less the underwriters' discount of $0.965625 per share. Total holdings include LP Units acquired in connection with a dividend of LP Units from Summit Materials Holdings GP, Ltd., of which Silverhawk is a shareholder. The acquisition of such LP Units was exempt pursuant to Rule 16a-9. The Reporting Person disclaims beneficial ownership of the securities reported herein as indirectly beneficially owned, except to the extent of his pecuniary interest therein. Pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934, the filing of this Form 4 shall not be deemed an admission that the Reporting Person is, for purposes of Section 16 or otherwise, the beneficial owner of any equity securities covered by this statement. /s/Anne Lee Benedict, as Attorney-in-Fact 2015-08-13