X0306 4 2015-08-11 0 0001621563 Summit Materials, Inc. SUM 0001484870 Blackstone Holdings II L.P. C/O THE BLACKSTONE GROUP L.P. 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 0001464695 Blackstone Holdings I/II GP Inc C/O THE BLACKSTONE GROUP L.P. 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 0001393818 Blackstone Group L.P. 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 0001404071 Blackstone Group Management L.L.C. C/O THE BLACKSTONE GROUP L.P. 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 0001070844 SCHWARZMAN STEPHEN A C/O THE BLACKSTONE GROUP L.P. 345 PARK AVENUE NEW YORK NY 10154 0 0 1 0 LP Units of Summit Materials Holdings L.P. 2015-08-11 4 S 0 13739945 D Class A Common Stock 13739945 30781057 I See Footnotes LP Units of Summit Materials Holdings L.P. 2015-08-11 4 S 0 2896494 D Class A Common Stock 2896494 6488901 I See Footnotes LP Units of Summit Materials Holdings L.P. 2015-08-11 4 S 0 261315 D Class A Common Stock 261315 585415 I See Footnotes LP Units of Summit Materials Holdings L.P. 2015-08-11 4 S 0 22143 D Class A Common Stock 22143 49605 I See Footnotes LP Units of Summit Materials Holdings L.P. 2015-08-11 4 S 0 12867 D Class A Common Stock 12867 28826 I See Footnotes Pursuant to the terms of an exchange agreement, dated as of March 11, 2015, limited partnership units of Summit Materials Holdings L.P. ("LP Units") held by the Reporting Persons are exchangeable for shares of the issuer's Class A common stock on a one-for-one basis. The Reporting Persons 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 previously reported as being indirectly beneficially owned by the Reporting Persons through Summit Materials Holdings GP, Ltd. ("Summit GP"). The Reporting Persons acquired direct ownership of such LP Units in connection with a dividend of LP Units by Summit GP, of which the Blackstone Funds (as defined below) are shareholders. The acquisitions were exempt under Rules 16a-9 and 16a-13. Reflects securities of the issuer held directly by Blackstone Capital Partners (Delaware) V-NQ L.P. (f/k/a Blackstone Capital Partners (Cayman) V-NQ L.P.). Reflects securities of the issuer held directly by Blackstone Capital Partners (Delaware) NQ V-AC L.P. (f/k/a Blackstone Capital Partners (Cayman) NQ V-AC L.P.). Reflects securities of the issuer held directly by Summit BCP Intermediate Holdings L.P. The general partner of Summit BCP Intermediate Holdings L.P. is Summit BCP Intermediate Holdings GP, Ltd. Summit BCP Intermediate Holdings GP, Ltd. is owned by Blackstone Capital Partners (Delaware) V-NQ L.P., Blackstone Capital Partners (Delaware) NQ V-AC L.P., Blackstone Family Investment Partnership (Delaware) V-NQ L.P. and Blackstone Participation Partnership (Delaware) V-NQ L.P. Reflects securities of the issuer held directly by Blackstone Family Investment Partnership (Delaware) V-NQ L.P. (f/k/a Blackstone Family Investment Partnership (Cayman) V-NQ L.P.). Reflects securities of the issuer held directly by Blackstone Participation Partnership (Delaware) V-NQ L.P. (f/k/a Blackstone Participation Partnership (Cayman) V-NQ L.P., and collectively with Blackstone Capital Partners (Delaware) V-NQ L.P., Blackstone Capital Partners (Delaware) NQ V-AC L.P., Summit BCP Intermediate Holdings L.P. and Blackstone Family Investment Partnership (Delaware) V-NQ L.P., the "Blackstone Funds"). The general partner of each of Blackstone Capital Partners (Delaware) V-NQ L.P. and Blackstone Capital Partners (Delaware) NQ V-AC L.P. is Blackstone Management Associates (Cayman) V-NQ L.P. The general partners of each of Blackstone Management Associates (Cayman) V-NQ L.P., Blackstone Family Investment Partnership (Delaware) V-NQ L.P. and Blackstone Participation Partnership (Delaware) V-NQ L.P. are Blackstone LR Associates (Cayman) V-NQ Ltd. and BCP V-NQ GP L.L.C. Blackstone Holdings II L.P. is the sole member of BCP V-NQ GP L.L.C. and the controlling shareholder of Blackstone LR Associates (Cayman) V-NQ Ltd. The general partner of Blackstone Holdings II L.P. is Blackstone Holdings I/II GP Inc. The sole shareholder of Blackstone Holdings I/II GP Inc. is The Blackstone Group L.P. The general partner of The Blackstone Group L.P. is Blackstone Group Management L.L.C. Blackstone Group Management L.L.C. is wholly owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. Due to the limitations of the electronic filing system Blackstone Capital Partners (Delaware) V-NQ L.P., Blackstone Capital Partners (Delaware) NQ V-AC L.P., Summit BCP Intermediate Holdings L.P., Summit BCP Intermediate Holdings GP, Ltd., Blackstone Family Investment Partnership (Delaware) V-NQ L.P., Blackstone Participation Partnership (Delaware) V-NQ L.P., Blackstone Management Associates (Cayman) V-NQ L.P., BCP V-NQ GP L.L.C. and Blackstone LR Associates (Cayman) V-NQ Ltd. are filing a separate Form 4. Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person. Each of the Reporting Persons (other than the Blackstone Funds to the extent they directly hold securities reported herein), disclaims beneficial ownership of the securities held by the Blackstone Funds, except to the extent of such Reporting Person's pecuniary interest therein, if any, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934, each of the Reporting Persons (other than the Blackstone Funds to the extent they directly hold securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the reported securities for purposes of Section 16 or for any other purpose. BLACKSTONE HOLDINGS II L.P., By: Blackstone Holdings I/II GP Inc., its general partner, By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 2015-08-13 BLACKSTONE HOLDINGS I/II GP INC., By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 2015-08-13 THE BLACKSTONE GROUP L.P., By: Blackstone Group Management L.L.C., its general partner, By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 2015-08-13 BLACKSTONE GROUP MANAGEMENT L.L.C., By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 2015-08-13 /s/ STEPHEN A. SCHWARZMAN 2015-08-13