SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL OMB Number: 3235-0104 Estimated average burden hours per response: 0.5

1. Name and Address of Reporting Person* LONGLEAF PARTNERS FUNDS TRUST (Last) (First) (Middle) C/O SOUTHEASTERN ASSET MANAGEMENT 6410 POPLAR AVE, SUITE 900 (Street) MEMPHIS TN 38119 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 06/17/2019	3. Issuer Name and Ticker or Trading Symbol Summit Materials, Inc. [ SUM ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)	5. If Amendment, Date of Original Filed (Month/Day/Year)
			6. Individual or Joint/Group Filing (Check Applicable Line) X Form filed by One Reporting Person Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Class A Common Stock	12,699,444	D

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

Remarks:

This Form 3 is filed by Longleaf Partners Funds Trust on behalf of Longleaf Partners Small Cap Fund. As a result of converting from a Schedule 13G to a Schedule 13D, Longleaf Partners Small-Cap Fund may be deemed a "beneficial owner" of more than 10% of the company's Class A Common Stock for Section 16 purposes under Rule 16a-1(a)(1). As permitted by Rule 16a-1, this Form 3 filing shall not be deemed an admission that Longleaf Partners Funds Trust or Longleaf Partners Small Cap Fund is the beneficial owner of more than 10% of the company's Class A Common Stock for Section 16 purposes. The number of securities reported in Table I herein is included in Table I of the Form 3 filed by Southeastern Asset Management, Inc.

	/s/ Andrew R. McCarroll, General Counsel, Southeastern Asset Management, Inc. on behalf of Longleaf Partners Funds Trust	06/17/2019
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.