Power of Attorney
 The undersigned hereby constitutes and appoints Stanley L. Ferguson,
Jessica A. Garascia,Jonathan Dorfman, and Kimberly Ericksen, signing
singly, as the undersigned's true and lawful attorney-in-fact
to:
 (1) execute and file by whatever means required, for and on
behalf of the undersigned, Forms 3, 4, 5 (hereinafter the "Forms") in
accordance with Section 16 of the Securities Exchange Act of 1934, as
amended (the "Exchange Act"), and the rules thereunder;
 (2) do and perform any and all acts for and on behalf of the
undersigned which may be necessary or desirable to complete the
execution of any such Forms and the timely filing of such Forms with
the United States Securities and Exchange Commission ("SEC") and any
other entity or person; and
 (3) take any other action of any type whatsoever in connection
with the foregoing which, in the opinion of such attorney-in-fact, may
be of benefit to, in the best interest of, or legally required by, the
undersigned, it being understood that the documents executed by such
attorney-in-fact on behalf of the undersigned pursuant to this Power of
Attorney shall be in such form and shall contain such terms and
conditions as such attorney-in-fact may approve in his or her
discretion.
 The undersigned acknowledges that the foregoing attorneys-in-
fact, in serving in such capacity at the request of the undersigned,
are not assuming any of the undersigned's responsibilities to comply
with Section 16 of the Exchange Act.
 This Power of Attorney shall be effective on the date set forth
below and shall continue in full force and effect until the date on
which the undersigned shall cease to be subject to Section 16 of the
Exchange Act and the rules thereunder or until such earlier date on
which written notification executed by the undersigned is filed with
the SEC expressly revoking this Power of Attorney.
 IN WITNESS WHEREOF, the undersigned has caused this Power of
Attorney to be executed effective the 1st day of July, 2015.
/s/Richard P. Lavin