Exhibit 24

                               POWER OF ATTORNEY
                     FOR SECTION 16 REPORTING OBLIGATIONS

        KNOW ALL BY THESE PRESENTS, that the undersigned hereby makes,
constitutes and appoints James F. Major, Jr., Lanesha T. Minnix, Paul Street and
Jason Ritter signing singly, as the undersigned's true and lawful attorney-in-
fact, with full power and authority as hereinafter described on behalf of and in
the name, place and stead of the undersigned to:

(1)     prepare, execute, acknowledge, deliver and file Forms 3, 4, and 5
        (including any amendments thereto) with respect to the securities of BMC
        Stock Holdings, Inc., a Delaware corporation, or any successor thereto
        (the "Company"), with the U.S. Securities and Exchange Commission, any
        national securities exchanges and the Company, as considered necessary
        or advisable under Section 16(a) of the Securities Exchange Act of 1934
        and the rules and regulations promulgated thereunder, as amended from
        time to time (the "Exchange Act");

(2)     seek or obtain, as the undersigned's representative and on the
        undersigned's behalf, information of transactions in the Company's
        securities from any third-party, including brokers, employee benefit
        plan administrators and trustees, and the undersigned hereby authorizes
        any such person to release any such information to the undersigned and
        approves and ratifies any such release of information; and

(3)     perform any and all other acts which in the discretion of such attorney-
        in-fact is necessary or desirable for and on behalf of the undersigned
        in connection with the foregoing.

The undersigned acknowledges that:

(1)     this Power of Attorney authorizes, but does not require, such attorney-
        in-fact to act in his or her discretion on information provided to such
        attorney-in-fact without independent verification of such information;

(2)     any documents prepared and/or executed by such attorney-in-fact on
        behalf of the undersigned pursuant to this Power of Attorney will be in
        such form and will contain such information and disclosure as such
        attorney-in-fact, in his or her discretion, deems necessary or
        desirable;

(3)     neither the Company nor such attorney-in-fact assumes (i) any liability
        for the undersigned's responsibility to comply with the requirement of
        the Exchange Act, (ii) any liability of the undersigned for any failure
        to comply with such requirements, or (iii) any obligation or liability
        of the undersigned for profit disgorgement under Section 16(b) of the
        Exchange Act; and

(4)     this Power of Attorney does not relieve the undersigned from
        responsibility for compliance with the undersigned's obligations under
        the Exchange Act, including without limitation the reporting
        requirements under Section 16 of the Exchange Act.

        The undersigned hereby gives and grants the foregoing attorney-in-fact
full power and authority to do and perform all and every act and thing
whatsoever requisite, necessary or appropriate to be done in and about the
foregoing matters as fully to all intents and purposes as the undersigned might
or could do if present, hereby ratifying all that such attorney-in-fact of, for
and on behalf of the undersigned, shall lawfully do or cause to be done by
virtue of this Power of Attorney.

        This Power of Attorney shall remain in full force and effect until
revoked by the undersigned in a signed writing delivered to such attorney-in-
fact.

        IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to
be executed as of this 27th day of July, 2017.

                                        By:    /s/ Mark A. Alexander
                                               ---------------------
                                        Name:  Mark A. Alexander
                                        Title: Director