Builders FirstSource, Inc.

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers. On May 18, 2026, Builders FirstSource, Inc. (the “Company”) announced that, as part of its planned leadership transition, its Board of Directors (the “Board”) appointed Mike Hiller, Chief Talent Officer of the Company, as Chief Operating Officer-Designate effective May 18, 2026. Mr. Hiller will succeed Steve Herron, as Chief Operating Officer effective December 31, 2026. Mr. Herron has served as Chief Operating Officer of the Company since March 2023 and is retiring after over 15 years of dedicated service to the Company. Mr. Hiller, 52, was appointed as Chief Talent Officer of the Company in November 2024. Prior to this appointment, he served as President - Central Division, since January 2021. Prior to joining the Company, Mr. Hiller served in various roles at BMC Stock Holdings, Inc., including Vice President - Intermountain Region from January 2017 to December 2020, Area Manager - Colorado from January 2015 to December 2016, and Area Manager - Utah from October 2011 to December 2014. Mr. Hiller has over 20 years of experience in the building products industry. He holds a Master of Business Administration and graduate certificate in finance from Westminster University. Additionally, the Board appointed Coley O’Brien to succeed Mr. Hiller as Chief Human Resources Officer, effective May 18, 2026. Mr. O’Brien joins the Company from The Wendy’s Company, where he was Chief People Officer since March 2018. The information required by Item 5.02(c)(3) of Form 8-K for Mr. Hiller has not been determined as of the date hereof. The Company will provide such information, if applicable, in an amendment to this Form 8-K within four (4) business days after the information is determined or becomes available.

Item 5.07 Submission of Matters to a Vote of Security Holders. The owners of 97,557,384 shares of the Company’s common stock, representing 88.20% of the voting power of all the shares of common stock issued and outstanding on March 16, 2026, the record date for the meeting, were represented at the Annual Meeting. Each share of common stock was entitled to one vote at the Annual Meeting. At the Annual Meeting, the Company’s stockholders voted on the following five proposals, as described in the Company’s 2026 Proxy Statement, and cast their votes as stated below. Proposal No. 1: Election of Directors. Nominee For Against Abstain Broker Non-Vote ────────────────────────────────────────────────────────────────────────────────────── Paul S. Levy 83,059,970 5,605,020 64,482 8,827,912 Cheryl Ainoa 88,396,041 268,996 64,435 8,827,912 Cory J. Boydston 85,157,525 3,454,536 117,411 8,827,912 James O'Leary 87,641,001 1,023,805 64,666 8,827,912 Maria Renz 88,379,287 285,903 64,282 8,827,912 Craig Steinke 76,271,469 12,364,061 93,942 8,827,912 Proposal No. 2: Advisory vote on the 2025 compensation of the Company’s named executive officers. For Against Abstain Broker Non-Vote ─────────────────────────────────────────────────────────────── 86,126,013 2,333,519 269,940 8,827,912 Proposal No. 3: Ratification of the appointment of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting firm for year 2026. For Against Abstain Broker Non-Vote ─────────────────────────────────────────────────────────────── 93,169,372 4,333,634 54,378 0 Proposal No. 4: Approval of the Builders FirstSource, Inc. 2026 Equity Incentive Plan. The proposal to approve the Builders FirstSource, Inc. 2026 Equity Incentive Plan was approved. For Against Abstain Broker Non-Vote ─────────────────────────────────────────────────────────────── 86,712,552 1,885,973 130,947 8,827,912 Proposal No. 5: Approval of the Builders FirstSource, Inc. Employee Stock Purchase Plan. The proposal to approve the Builders FirstSource, Inc. Employee Stock Purchase Plan was approved. For Against Abstain Broker Non-Vote ───────────────────────────────────────────────────────────── 88,304,284 369,902 55,286 8,827,912

Item 7.01 Regulation FD Disclosure. On May 18, 2026, the Company issued a news release announcing the leadership transition noted above. A copy of the news release is attached hereto as Exhibit 99.1. Item 9.01 Financial Statements and Exhibits. (d) Exhibits. Exhibit No. Description ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── 99.1 News release issued by Builders FirstSource, Inc. on May 18, 2026. 104 Cover Page Interactive Data File - the cover page XBRL tags are embedded within the Inline XBRL document. All of the information included in Items 7.01 and 9.01 of this report and Exhibit 99.1 hereto is being furnished and shall not be deemed to be “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, and shall not be incorporated by reference in any filing under the Securities Act of 1933, as amended.