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): July 23, 2015

Builders FirstSource, Inc.

(Exact name of registrant as specified in its charter)

2001 Bryan Street, Suite 1600

Dallas, Texas 75201

(Address of principal executive offices, including zip code)

(214) 880-3500

(Registrant’s telephone number, including area code)

N/A

(Former name or former 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 (see General Instruction A.2. below):

On July 23, 2015, Builders FirstSource, Inc. (the “Company”) reported its preliminary results for the second quarter ended June 30, 2015, which are provided below. Such financial information includes the non-GAAP financial measures and other items discussed in Appendix A hereto. Appendix A hereto (incorporated herein by reference) also contains certain statements of the Company’s management regarding the use and purposes of the non-GAAP financial measures utilized. A reconciliation of the non-GAAP financial measures discussed below to the comparable GAAP financial measures is provided below.

The selected financial data presented below are preliminary, based upon estimates by the Company. Such preliminary financial data is subject to finalization of the Company’s quarterly financial statements and accounting procedures and should not be viewed as a substitute for full interim financial statements prepared in accordance with GAAP. The Company’s actual results may be materially different from the estimates set forth below and are not necessarily indicative of the Company’s results for the full fiscal quarter or any future period. The preliminary financial data included in this Current Report has been prepared by, and is the responsibility of, the management of the Company. PricewaterhouseCoopers LLP has not audited, reviewed, compiled or performed any procedures with respect to the accompanying preliminary financial data. Accordingly, PricewaterhouseCoopers LLP does not express an opinion or any other form of assurance with respect thereto.

Second Quarter 2015 Results Compared to Second Quarter 2014 Results

(See accompanying financial schedules for full financial details and reconciliations of Non-GAAP financial measures to their GAAP equivalents.)

2

Liquidity and Capital Resources

Financial Schedules

BUILDERS FIRSTSOURCE, INC. AND SUBSIDIARIES

Condensed Consolidated Statements of Operations

(unaudited)

3

BUILDERS FIRSTSOURCE, INC. AND SUBSIDIARIES

Sales by Product Category

(unaudited)

BUILDERS FIRSTSOURCE, INC. AND SUBSIDIARIES

Condensed Consolidated Balance Sheets

(unaudited)

4

BUILDERS FIRSTSOURCE, INC. AND SUBSIDIARIES

Condensed Consolidated Statements of Cash Flows

(unaudited)

5

BUILDERS FIRSTSOURCE, INC. AND SUBSIDIARIES

Supplemental Interest Expense Information

(unaudited)

BUILDERS FIRSTSOURCE, INC. AND SUBSIDIARIES

Reconciliation of Non-GAAP Financial Measures to their GAAP Equivalents

(unaudited)

6

Cautionary Notice

Statements in this current report on Form 8-K and the schedules hereto that are not purely historical facts or that necessarily depend upon future events, including statements about expected market share gains, forecasted financial performance or other statements about anticipations, beliefs, expectations, hopes, intentions or strategies for the future, may be forward-looking statements within the meaning of Section 21E of the Securities Exchange Act of 1934, as amended. Readers are cautioned not to place undue reliance on forward-looking statements. All forward-looking statements are based upon information available to Builders FirstSource, Inc. on the date this current report on Form 8-K was submitted. Builders FirstSource, Inc. undertakes no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise. Any forward-looking statements involve risks and uncertainties that could cause actual events or results to differ materially from the events or results described in the forward-looking statements, including risks or uncertainties related to the Company’s growth strategies, including gaining market share, or the Company’s revenues and operating results being highly dependent on, among other things, the homebuilding industry, lumber prices and the economy. Builders FirstSource, Inc. may not succeed in addressing these and other risks. Further information regarding factors that could affect our financial and other results can be found in the risk factors section of Builders FirstSource, Inc.’s most recent annual report on Form 10-K filed with the Securities and Exchange Commission. Consequently, all forward-looking statements in this release are qualified by the factors, risks and uncertainties contained therein.

7

SIGNATURES

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

Date: July 23, 2015

APPENDIX A

Use of Non-GAAP Financial Measures

We occasionally utilize financial measures and terms not calculated in accordance with accounting principles generally accepted in the United States (“GAAP”) in order to provide investors with an alternative method for assessing our operating results in a manner that enables investors to more thoroughly evaluate our current performance as compared to past performance. We also believe these non-GAAP measures provide investors with a better baseline for modeling our future earnings expectations. Our management uses these non-GAAP measures for the same purpose. We believe that our investors should have access to the same set of tools that we use in analyzing our results. These non-GAAP measures should be considered in addition to results prepared in accordance with GAAP, but should not be considered a substitute for or superior to GAAP results. Our calculation of Adjusted EBITDA is not necessarily comparable to similarly titled measures reported by other companies. We have provided a definition below for these non-GAAP financial measures, together with an explanation of why management uses these measures and why management believes that these non-GAAP financial measures are useful to investors. In addition, we have provided a reconciliation within the Earnings Release to reconcile these non-GAAP financial measures utilized therein to its equivalent GAAP financial measure.

Adjusted EBITDA

We define Adjusted EBITDA as GAAP net income (loss) before depreciation and amortization, interest expense, income taxes, and other non-cash or special items including asset impairments, facility closure costs, acquisition costs, and stock compensation expense. Our management uses Adjusted EBITDA as a supplemental measure in the evaluation of our business and believes that Adjusted EBITDA provides a meaningful measure of our performance because it eliminates the effects of period to period changes in taxes, costs associated with capital investments, interest expense, stock compensation expense, and other non-cash and non-recurring items. Adjusted EBITDA is not a financial measure calculated in accordance with GAAP. Accordingly, it should not be considered in isolation or as a substitute for net income (loss) or other financial measures prepared in accordance with GAAP. When evaluating Adjusted EBITDA, investors should consider, among other factors, (i) increasing or decreasing trends in Adjusted EBITDA, (ii) whether Adjusted EBITDA has remained at positive levels historically, and (iii) how Adjusted EBITDA compares to our debt outstanding. We provide a reconciliation of Adjusted EBITDA to GAAP net income (loss). Because Adjusted EBITDA excludes some, but not all, items that affect net income (loss) and may vary among companies, Adjusted EBITDA presented by us may not be comparable to similarly titled measures of other companies. Adjusted EBITDA does not give effect to the cash we must use to service our debt or pay income taxes and thus does not reflect the funds generated from or used in operations or actually available for capital investments.

Adjusted loss from continuing operations

We define adjusted loss from continuing operations as GAAP loss from continuing operations before non-cash or special items including acquisition costs, and warrant fair value adjustments. Our management uses adjusted loss from continuing operations as a supplemental measure in the evaluation of our business and believes that adjusted loss from continuing operations provides a meaningful measure of our performance because it eliminates the effects of period to period non-cash and non-recurring items. Adjusted loss from continuing operations is not a financial measure calculated in accordance with GAAP. Accordingly, it should not be considered in isolation or as a substitute for income (loss) from continuing operations or other financial measures prepared in accordance with GAAP. When evaluating adjusted loss from continuing operations, investors should consider, among other factors, (i) increasing or decreasing trends in adjusted loss from continuing operations, and (ii) whether adjusted loss from continuing operations has remained at positive levels historically. We provide a reconciliation of adjusted loss from continuing operations to GAAP loss from continuing operations. Because adjusted loss from continuing operations excludes some, but not all, items that affect loss from continuing operations and may vary among companies, adjusted loss from continuing operations presented by us may not be comparable to similarly titled measures of other companies.