SC TO-C

QuickLinks -- Click here to rapidly navigate through this document

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

SCHEDULE TO
(Rule 14d-100)

TENDER OFFER STATEMENT UNDER SECTION 14(d)(1) OR 13(e)(1)
OF THE SECURITIES EXCHANGE ACT OF 1934

ElkCorp
(Name of Subject Company (Issuer))

BMCA Acquisition Inc.,

Building Materials Corporation of America
(Names of Filing Persons — Offeror)

Common Stock, par value $1.00 per share
(Title of Class of Securities)

287456107
(CUSIP Number of Class of Securities)

Building Materials Corporation of America
1361 Alps Road
Wayne, NJ 07470
(201) 628-3000
Attention: John F. Rebele
(Name, Address and Telephone Numbers of Person
Authorized to Receive Notices and Communications on Behalf of Filing Persons)

Copies to:

Steven A. Seidman, Esq.
Maurice M. Lefkort, Esq.
Willkie Farr & Gallagher LLP
787 Seventh Avenue
New York, NY 10019-6099
(212) 728-8000

CALCULATION OF FILING FEE

Transaction Valuation	Amount of Filing Fee
Not applicable*	Not applicable*

*

A filing fee is not required in connection with this filing as it relates solely to preliminary communications made before the commencement of a tender offer.

o

Check the box if any part of the fee is offset as provided by Rule 0-11(a)(2) of the Exchange Act and identify the filing with which the offsetting fee was previously paid. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing. Amount Previously Paid: Form or Registration None Not Applicable Filing Party: Not Applicable Date Filed: Not Applicable No.:

ý

Check the box if the filing relates solely to preliminary communications made before the commencement of a tender offer.

Check the appropriate boxes below to designate any transactions to which the statement relates:

ý

third-party tender offer subject to Rule 14d-1.



o

issuer tender offer subject to Rule 13e-4.



o

going-private transaction subject to Rule 13e-3.



ý

amendment to Schedule 13D under Rule 13d-2.

        Check the following box if the filing is a final amendment reporting the results of the tender offer: o

SCHEDULE TO

        This Tender Offer Statement on Schedule TO is filed by Building Materials Corporation of America, a Delaware corporation ("BMCA"), and BMCA Acquisition Inc., a Delaware corporation (including any successor thereto, the "Purchaser"). Pursuant to Exchange Act Rule 14d-2 and General Instruction D to Schedule TO, this Schedule TO relates to pre-commencement communications by BMCA and the Purchaser.

EXHIBIT INDEX

Exhibit No.
99.1	Press Release, dated December 17, 2006.
99.2	Letter from Robert B. Tafaro, President and Chief Executive Officer of Building Materials Corporation of America, to Thomas D. Karol, Chairman of the Board and Chief Executive Officer of ElkCorp, dated December 17, 2006.

QuickLinks

SCHEDULE TO
EXHIBIT INDEX

EX-99.1

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 99.1

[LETTERHEAD]

FOR IMMEDIATE RELEASE

For more information, contact Building Materials Corporation of America at 973-317-5960

BMCA ANNOUNCES COMMENCEMENT OF ITS TENDER OFFER TO ACQUIRE ELKCORP

        December 17, 2006—Building Materials Corporation of America ("BMCA"), North America's largest roofing manufacturer, which operates under the name GAF Materials Corporation, today announced its intention to commence a tender offer to purchase all the outstanding shares of common stock of ElkCorp, par value $1.00 per share, at a price of $35.00 per share.

        The following are the principal terms of BMCA's offer:

Price:    BMCA, through an acquisition subsidiary, proposes to acquire ElkCorp through an all cash transaction at a price of $35.00 per share of ElkCorp common stock. The proposed price of $35.00 per share represents an approximate 40% premium over ElkCorp's closing price on November 3, 2006 ($25.18 per share), the trading day immediately preceding BMCA's filing of its Schedule 13D and ElkCorp's announcement of its sale process.

Regulatory:    As previously announced, the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act expired on December 6, 2006.

        Counsel to BMCA for the tender offer is Willkie Farr & Gallagher LLP.

        The Offer to Purchase, Letter of Transmittal and related documents will be mailed to stockholders of record when available and also will be made available for distribution to beneficial owners of ElkCorp's common stock.

        In connection with its announcement of the tender offer, BMCA today sent the following letter to Thomas D. Karol, Chairman of the Board of Directors and Chief Executive Officer of ElkCorp:

        December 17, 2006

Mr. Thomas D. Karol
Chairman of the Board and CEO
ElkCorp
14911 Quorum Drive, Suite 600
Dallas, TX 75254-1491

Dear Tom:

        We are today announcing that we will be commencing a tender offer for all outstanding Elk common shares at $35 per share. As you know, we have already received antitrust clearance and this offer is not conditional on financing.

        Tom, BMCA has been both open and direct in all its dealings with you, your colleagues, and outside advisors. Notwithstanding, Elk has refused to enter into discussions with us regarding our merger proposal or provide confidential information as it has with other bidders. Most recently, on Tuesday, December 12^th, our representatives contacted your financial advisors, UBS, seeking guidance on how best to proceed. UBS informed us that BMCA's merger proposal was scheduled to be considered at an Elk Board meeting on December 13^th and that they would be in a position to provide us with guidance in a call immediately after the meeting. Instead, we have heard nothing from your advisors, and they have since "gone off the air."

        You should know that, in light of the above, you have given us no choice but to take our offer directly to shareholders. Please be assured that we continue to stand ready to negotiate a definitive merger agreement directly with Elk, if it so chooses, and we believe this to be in the best interests of Elk, its shareholders and employees.

        All the best.

Sincerely,

/s/ Robert B. Tafaro Robert B. Tafaro
President and Chief Executive Officer

cc: Elk Board of Directors

2

# # #

BMCA INFORMATION

        Building Materials Corporation of America, which operates under the name of GAF Materials Corporation, is an indirect subsidiary of G-I Holdings Inc. With annual sales in 2005 approximating $2.0 billion, BMCA is North America's largest manufacturer of residential and commercial roofing products and specialty building products.

# # #

        THIS PRESS RELEASE IS FOR INFORMATIONAL PURPOSES ONLY AND DOES NOT CONSTITUTE AN OFFER TO BUY OR THE SOLICITATION OF AN OFFER TO SELL SHARES OF ELKCORP COMMON STOCK. THE TENDER OFFER IS BEING MADE ONLY PURSUANT TO THE OFFER TO PURCHASE, LETTER OF TRANSMITTAL AND RELATED MATERIALS THAT BMCA WILL SHORTLY BE DISTRIBUTING TO ELKCORP'S STOCKHOLDERS AND FILING WITH THE SECURITIES AND EXCHANGE COMMISSION. STOCKHOLDERS SHOULD READ CAREFULLY THE OFFER TO PURCHASE, LETTER OF TRANSMITTAL AND RELATED MATERIALS BECAUSE THEY CONTAIN IMPORTANT INFORMATION, INCLUDING THE VARIOUS TERMS OF, AND CONDITIONS TO, THE TENDER OFFER. STOCKHOLDERS MAY OBTAIN A FREE COPY OF THE TENDER OFFER STATEMENT ON SCHEDULE TO, THE OFFER TO PURCHASE, LETTER OF TRANSMITTAL AND OTHER DOCUMENTS THAT BMCA WILL SHORTLY BE FILING WITH THE SECURITIES AND EXCHANGE COMMISSION AT THE COMMISSION'S WEBSITE AT WWW.SEC.GOV. STOCKHOLDERS ARE URGED TO CAREFULLY READ THESE MATERIALS PRIOR TO MAKING ANY DECISION WITH RESPECT TO THE TENDER OFFER.

# # #

FORWARD-LOOKING STATEMENTS

This release contains some forward-looking statements as defined by the federal securities laws which are based on our current expectations and assumptions, which are subject to a number of risks and uncertainties that could cause actual results to differ materially from those anticipated, projected or implied. We undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise.

3

QuickLinks

[LETTERHEAD]
BMCA ANNOUNCES COMMENCEMENT OF ITS TENDER OFFER TO ACQUIRE ELKCORP

EX-99.2

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 99.2

[LETTERHEAD]

December 17, 2006

Mr. Thomas D. Karol
Chairman of the Board and CEO
ElkCorp
14911 Quorum Drive, Suite 600
Dallas, TX 75254-1491

Dear Tom:

        We are today announcing that we will be commencing a tender offer for all outstanding Elk common shares at $35 per share. As you know, we have already received antitrust clearance and this offer is not conditional on financing.

        Tom, BMCA has been both open and direct in all its dealings with you, your colleagues, and outside advisors. Notwithstanding, Elk has refused to enter into discussions with us regarding our merger proposal or provide confidential information as it has with other bidders. Most recently, on Tuesday, December 12^th, our representatives contacted your financial advisors, UBS, seeking guidance on how best to proceed. UBS informed us that BMCA's merger proposal was scheduled to be considered at an Elk Board meeting on December 13^th and that they would be in a position to provide us with guidance in a call immediately after the meeting. Instead, we have heard nothing from your advisors, and they have since "gone off the air."

        You should know that, in light of the above, you have given us no choice but to take our offer directly to shareholders. Please be assured that we continue to stand ready to negotiate a definitive merger agreement directly with Elk, if it so chooses, and we believe this to be in the best interests of Elk, its shareholders and employees.

        All the best.

Sincerely,

/s/ Robert B. Tafaro Robert B. Tafaro
President and Chief Executive Officer

cc: Elk Board of Directors

QuickLinks

[LETTERHEAD]