Exhibit 99.1

                            Explanation of Responses:


(1) Building Products, LLC is the direct record owner of 17,305,103 shares of
Builders FirstSource, Inc. Common Stock ("Common Stock"). By virtue of its
position as a member of Building Products, LLC and pursuant to the Amended and
Restated Limited Liability Company Agreement of Building Products, LLC, Warburg
Pincus Private Equity IX, L.P., a Delaware limited partnership ("WP IX"), may be
deemed to be the beneficial owner of 8,652,551.5 shares of Common Stock. The
sole general partner of WP IX is Warburg Pincus IX LLC, a New York limited
liability company ("WP IX LLC"); Warburg Pincus Partners LLC, a New York limited
liability company ("WPP LLC"), is the sole member of WP IX LLC; Warburg Pincus &
Co., a New York general partnership ( "WP"), is the managing member of WPP LLC;
Warburg Pincus LLC, a New York limited liability company ("WP LLC"), manages WP
IX; and Charles R. Kaye and Joseph P. Landy are each Managing General Partners
of WP and Co-Presidents and Managing Members of WP LLC. By reason of the
provisions of Rule 16a-1 of the Securities Exchange Act of 1934 (the "Act"), WP,
WP LLC, WPP LLC, WP IX LLC, Mr. Kaye and Mr. Landy may be deemed to be the
beneficial owners of the securities reported as beneficially owned by WP IX.
Each of WP, WP LLC, WPP LLC, WP IX LLC, Mr. Kaye and Mr. Landy all disclaim
beneficial ownership of all shares of Common Stock except to the extent of any
indirect pecuniary interest therein.

Through a series of purchases on November 30, 2006 and December 1, 2006, WP IX
is the direct record owner of 51,200 shares of Common Stock, and through a
series of purchases on December 4, 2006, WP IX is the direct record owner of an
additional 21,300 shares of Common Stock. By reason of the provisions of Rule
16a-1 of the Securities Exchange Act of 1934 (the "Act"), WP, WP LLC, WPP LLC,
WP IX LLC, Mr. Kaye and Mr. Landy may be deemed to be the beneficial owners of
the securities reported as beneficially owned by WP IX. Each of WP, WP LLC, WPP
LLC, WP IX LLC, Mr. Kaye and Mr. Landy all disclaim beneficial ownership of all
shares of Common Stock except to the extent of any indirect pecuniary interest
therein.

Mr. Graff, who became a director of Builders FirstSource, Inc. on February 27,
2006, is a partner of WP, and a member and Managing Director of WP LLC. As such,
Mr. Graff may be deemed to have an indirect pecuniary interest (within the
meaning of 16a-1 of the Act) in an indeterminate portion of the securities
reported as beneficially owned by WP IX. Mr. Graff disclaims beneficial
ownership of such securities except to the extent of any indirect pecuniary
interest therein. Mr. Graff does not directly own any shares of Common Stock.