UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported): January 10, 2023

Summit Materials, Inc.

Summit Materials, LLC

(Exact name of registrant as specified in its charter)

1801 California Street, Suite 3500

Denver, Colorado 80202

(Address of Principal Executive Offices) (Zip Code)

Registrant’s telephone number, including area code: (303) 893-0012

Not Applicable

(Former Name or Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 or Rule 12b-2 of the Securities Exchange Act of 1934.

Emerging growth company ¨

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ¨

Amendment No. 6 to Amended and Restated Credit Agreement

On January 10, 2023, Summit Materials, LLC (“Summit LLC”), an indirect subsidiary of Summit Materials, Inc., and the guarantors party thereto entered into Amendment No. 6 (“Amendment No. 6”) to the Amended and Restated Credit Agreement, dated as of July 17, 2015 (together with Amendment No. 1, dated as of January 19, 2017, Amendment No. 2, dated as of November 21, 2017, Amendment No. 3, dated as of May 22, 2018, Amendment No. 4, dated as of February 25, 2019 and Amendment No. 5, dated as of December 14, 2022, the “Credit Agreement”), governing Summit LLC’s senior secured credit facilities, among Summit LLC, as borrower, the guarantors party thereto, the several banks and other financial institutions or entities party thereto, Bank of America, N.A., as administrative agent, collateral agent, L/C issuer and swing line lender and the other parties thereto.

Amendment No. 6 amended the Credit Agreement to, among other things, in respect of the revolving credit facility thereunder (the “Revolving Credit Facility”), (a) increase the total aggregate commitments under the Revolving Credit Facility from $345.0 million to $395.0 million, (b) convert the existing LIBOR-based rate applicable to the Revolving Credit Facility to a Term SOFR Rate with a SOFR adjustment of 0.10% per annum and a floor of zero and (c) extend the maturity date of the Revolving Credit Facility to January 10, 2028 (five years from the effective date of Amendment No. 6), provided that the maturity date will be December 14, 2026 if more than $125.0 million in aggregate principal amount of Summit LLC’s senior unsecured notes due 2027 remain outstanding as of such date. All other material terms and provisions of the Revolving Credit Facility remain substantially the same as the terms and provisions in place immediately prior to the effectiveness of Amendment No. 6.

The foregoing description of Amendment No. 6 does not purport to be complete and is qualified in its entirety by reference to the full text of Amendment No. 6 which is filed herewith as Exhibit 10.1 and is incorporated herein by reference.

The information set forth in Item 1.01 is incorporated by reference into this Item 2.03.

(d) Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, each registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.