<PAGE>   1

                                                                    Exhibit 4.12
                                                                    ------------


                          SECOND SUPPLEMENTAL INDENTURE

                          dated as of December 4, 2000

                                       to

                                    INDENTURE

                          dated as of December 3, 1998

                                      among



                   BUILDING MATERIALS CORPORATION OF AMERICA,

                                   as Issuer,

                  BUILDING MATERIALS MANUFACTURING CORPORATION


                                       and

                   BUILDING MATERIALS INVESTMENT CORPORATION,

                             as Original Guarantors,

                   THE ADDITIONAL GUARANTORS SIGNATORY HERETO

                                       and

                              THE BANK OF NEW YORK,

                                   as Trustee


<PAGE>   2



                  This SECOND SUPPLEMENTAL INDENTURE to the Indenture (as
defined below) (the "Second Supplemental Indenture") dated as of December 4,
2000, is made among BUILDING MATERIALS CORPORATION OF AMERICA, a Delaware
corporation (the "Company"), BUILDING MATERIALS MANUFACTURING CORPORATION and
BUILDING MATERIALS INVESTMENT CORPORATION, each a Delaware corporation
wholly-owned by the Company (the "Original Guarantors"), THE BANK OF NEW YORK, a
New York banking corporation, as trustee (the "Trustee"), and the ADDITIONAL
GUARANTORS signatory hereto (the "Additional Guarantors," and together with the
Original Guarantors, the "Guarantors") and amends the Indenture, dated as of
December 3, 1998, between the Company and the Trustee, as amended by the First
Supplemental Indenture, dated January 1, 1999, among the Company, the Original
Guarantors and the Trustee (as further amended from time to time, the
"Indenture").


                                R E C I T A L S:
                                ----------------

                  A. Pursuant to the Indenture, the Company issued $155 million
in aggregate principal amount at maturity of its 8% Senior Notes due 2008 (the
"Securities").

                  B. The Company, the Guarantors and the Trustee desire by this
Second Supplemental Indenture to amend certain provisions of the Indenture.

                  C. Consent to the amendments set forth in Article I herein
have been solicited from the holders of record as of November 27, 2000, of the
Securities pursuant to a Consent Solicitation Statement dated the 6th day of
December 2000, as supplemented by the Supplement to Consent Solicitation
Statement dated the 20th day of December 2000 (the "Consent Solicitation
Statement"). The effectiveness of this Second Supplemental Indenture is
conditioned upon the receipt of the Requisite Consents (as defined in the
Consent Solicitation Statement).

                  D. Capitalized terms used herein without definition shall have
the meanings assigned to them in the Indenture.

                  NOW, THEREFORE, it is hereby agreed as follows:


                                    ARTICLE I

                                   AMENDMENTS

                  SECTION 1.01. Certain Defined Terms. The following provisions
set forth in the definitions in Section 1.01 of the Indenture are hereby amended
as follows:



                                       2
<PAGE>   3

                  (a) The definition of "Credit Agreement" is hereby amended and
restated in its entirety to read as follows:

                  "Credit Agreement" means the amended and restated Credit
                  Agreement, dated as of December 4, 2000, among the Company,
                  the lenders party thereto, Fleet National Bank, as
                  Documentation Agent, Bear Stearns Corporate Lending Inc., as
                  Syndication Agent, and The Bank of New York, as Swing Line
                  Lender and as Administrative Agent, as the same may be
                  amended, supplemented, Refinanced (including by the DIP
                  Facility) or otherwise modified from time to time."

                  (b) The following defined terms are added to Section 1.01 in
the appropriate alphabetical order:

                  "Collateral Agent Agreement" means the collateral agent
                  agreement, dated as of December 4, 2000, among the Company,
                  the Subsidiary Guarantors identified therein, The Chase
                  Manhattan Bank, Fleet National Bank, The Bank of New York, as
                  Collateral Agent, The Bank of New York, as Indenture Trustee,
                  and The Bank of New York, as Administrative Agent under the
                  Credit Agreement and the New Credit Agreement, as the same may
                  be amended, supplemented or otherwise modified from time to
                  time.

                  "Consent Solicitation Statement" means that certain consent
                  solicitation statement of the Company and Building Materials
                  Manufacturing Corporation dated December 6, 2000, as
                  supplemented on December 20, 2000."

                  "DIP Facility" has the meaning ascribed to such term in the
                  New Credit Agreement.

                  "New Credit Agreement" means the secured credit agreement,
                  dated as of December 4, 2000, among the Company, the Lenders
                  party thereto, and The Bank of New York, as Swing Line Lender
                  and as Administrative Agent, as the same may be amended,
                  supplemented, Refinanced (including by the DIP Facility) or
                  otherwise modified from time to time.

                  "Other Indebtedness" means the obligations under that certain
                  promissory note issued by the Company to The Chase Manhattan
                  Bank dated as of the effective date of the New Credit
                  Agreement which was issued to replace the obligations of the


                                       3
<PAGE>   4

                  Company under that certain platinum bullion lease effective
                  December 1, 2000 (and any subsequent confirmations of such
                  lease entered into prior to the effective date of the New
                  Credit Agreement) and approximately $3.5 million of
                  obligations under a standby letter of credit, dated as of June
                  4, 1999, issued by Fleet National Bank in connection with the
                  Company's Shafter, California facility, as each may be
                  amended, supplemented, refinanced (including by the DIP
                  Facility) or otherwise modified from time to time and any
                  hedging obligations entered into with counterparties that are
                  the lenders or affiliates of the lenders under the New Credit
                  Agreement and the Credit Agreement.

                  SECTION 1.02. Section 4.01 of the Indenture is hereby amended
and restated in its entirety to read as follows:

                  "The Company shall pay, or cause to be paid, the principal of
and interest on the Securities on the dates and in the manner provided herein
and in the Securities; provided, however, that Holders that consented to the
Proposed Amendments (as defined in the Consent Solicitation Statement) will
receive quarterly interest payments on March 1, June 1, September 1, December 1
of each year, commencing June 1, 2001. The record dates for such interest
payments shall be the preceding February 15, May 15, August 15 and November 15.
Principal or interest shall be considered paid on the date due if the Trustee or
Paying Agent holds on that date money designated for and sufficient to pay all
principal and interest payable in cash in each case as then due. The Company
shall pay interest on overdue principal, as the case may be, at the rate
specified therefor in the Securities."

                  SECTION 1.03. Section 4.09(b) of the Indenture is hereby
amended and restated in its entirety to read as follows:

                  "(b) Notwithstanding the foregoing, there may be issued the
following Debt:

                           (1) The Securities;

                           (2) (i) Debt of the Company Issued to and held by a
         Wholly-Owned Recourse Subsidiary of the Company and (ii) Debt of a
         Recourse Subsidiary of the Company Issued to and held by the Company or
         a Wholly-Owned Recourse Subsidiary of the Company; provided that any
         subsequent transfer of such Debt (other than to the Company or to a
         Wholly-Owned Recourse Subsidiary of the Company) shall be deemed, in
         each case, to constitute the Issuance of such Debt by the Company or
         such Subsidiary;



                                       4
<PAGE>   5

                           (3) Debt the proceeds of which are used to acquire
         assets of the Company and its Subsidiaries; provided that, after giving
         effect to the Issuance of any such Debt that otherwise complies with
         this clause (3), the aggregate amount of all Debt then outstanding at
         any time under this clause (3), including all Refinancings thereof then
         outstanding, shall not at any time exceed $80,000,000;

                           (4) Acquired Debt;

                           (5) (x) Debt outstanding on the Issue Date (including
         the Deferred Coupon Notes, the 2005 Notes, the 2006 Notes and the 2007
         Notes) and (y) Debt Issued to Refinance any Debt permitted by clause
         (a), this clause (5) or by clauses (1), (3), (7), (9) and (10) of this
         Section 4.09(b); provided that, in the case of a Refinancing, (i) the
         amount of the Debt so Issued shall not exceed the principal amount or
         the accreted value (in the case of Debt Issued at a discount) of the
         Debt so Refinanced plus, in each case, the reasonable costs incurred by
         the issuer in connection with such Refinancing, (ii) the Average Life
         and Stated Maturity of the Debt so Issued shall equal or exceed that of
         the Debt so Refinanced, (iii) the Debt so Issued shall not rank senior
         in right of payment to the Debt being Refinanced, (iv) if the Debt
         being Refinanced does not bear interest in cash prior to a specified
         date, the Refinancing Debt shall not bear interest in cash prior to
         such specified date, (v) if the Debt being Refinanced is Debt permitted
         by clause (3), such Refinancing Debt is not secured by any assets not
         securing the Debt so Refinanced or improvements or additions thereto,
         or replacements thereof, and (vi) the obligors with respect to the
         Refinancing Debt shall not include any Persons who were not obligors
         (including predecessors thereof) with respect to the Debt being
         Refinanced;

                           (6) Non-Recourse Debt of a Non-Recourse Subsidiary of
         the Company and Guarantees of Non-Recourse Debt of Non-Recourse
         Subsidiaries which Guarantees are recourse only to the stock of the
         Non-Recourse Subsidiaries;

                           (7) Debt under the Credit Agreement in an aggregate
         principal amount not to exceed $110,000,000;

                           (8) Debt secured by Receivables, including to
         Refinance the Receivables Financing Agreement, provided that the amount
         of such Debt does not exceed 85% of the face amount of the Receivables;

                           (9) Debt represented by the Other Indebtedness or any
         Refinancing thereof;

                           (10) Debt represented by the New Credit Agreement in
         an aggregate principal amount not to exceed $100,000,000;



                                       5
<PAGE>   6

                           (11) Debt permitted to be incurred under the Credit
         Agreement or the New Credit Agreement as each such agreement was in
         effect on the effective date of the New Credit Agreement; and

                           (12) Beginning on the first anniversary of the
         effective date of the New Credit Agreement, Debt (other than Debt
         identified in clauses (1) through (11) above) in an aggregate principal
         amount outstanding at any one time not to exceed $30,000,000."

                  SECTION 1.04. (a) Sections 4.10(a) and (b) of the Indenture
are hereby amended by adding the clause "Subject to Section 4.10(c) below," to
the beginning of each such section.

                  (b) Section 4.10 of the Indenture is hereby further amended by
adding a new clause (c) to read as follows:

                  "Notwithstanding the foregoing, until the date that is the
third anniversary following the effective date of the New Credit Agreement, the
Company will be permitted to make a Restricted Payment to the extent, and only
to the extent, that such payment is permitted by the terms of the Credit
Agreement or the New Credit Agreement as each such agreement was in effect on
the effective date of the New Credit Agreement. Following the date that is the
third anniversary of the effective date of the New Credit Agreement, the Company
will only be permitted to make Restricted Payments pursuant to paragraph 4.10(a)
above in an aggregate principal amount not to exceed $15,000,000 in any fiscal
year."

                  SECTION 1.05. Section 4.11 of the Indenture is hereby amended
and restated in its entirety to read as follows:

                  "Limitation on Liens. The Company shall not, and shall not
permit any of its Subsidiaries to, directly or indirectly, incur or suffer to
exist any Liens upon their respective property or assets whether owned on the
Issue Date or acquired after such date, or on any income or profits therefrom,
unless the Securities are equally and ratably secured by such Lien; provided
that if the Debt secured by such Lien is subordinate or junior in right of
payment to the Securities then the Lien securing such Debt shall be subordinate
or junior in priority to the Lien securing the Securities at least to the same
extent as such Debt is subordinate or junior to the Securities.

                  The foregoing restrictions shall not apply to:

                  (1) Liens existing on the Issue Date;

                  (2) Permitted Liens;

                  (3) Purchase money Liens on assets of the Company and its
         Subsidiaries or improvements or additions thereto existing or created
         within 180 days after the time of acquisition of or improvements or


                                       6
<PAGE>   7

         additions to such assets, or replacements thereof; provided that (i)
         such acquisition, improvement or addition is otherwise permitted by
         this Indenture, (ii) the principal amount of Debt (including Debt in
         respect of Capitalized Lease Obligations) secured by each such Lien on
         each asset shall not exceed the cost (including all such Debt secured
         thereby, whether or not assumed) of the item subject thereto, and such
         Liens shall attach solely to the particular item of property so
         acquired, improved or added and any additions or accessions thereto, or
         replacements thereof, and (iii) the aggregate amount of Debt secured by
         Liens permitted by this clause (3) shall not at any time exceed
         $40,000,000;

                  (4) Liens to secure Refinancing of any Debt secured by Liens
         described in clauses (l)-(3) above and (5) below; provided that (i)
         Refinancing does not increase the principal amount of Debt being so
         Refinanced and (ii) the Lien of the Refinancing Debt does not extend to
         any asset not securing the Debt being Refinanced or improvements or
         additions thereto, or replacements thereof;

                  (5) Liens securing Acquired Debt; provided that (i) any such
         Lien secured the Acquired Debt at the time of the incurrence of such
         Acquired Debt by the Company or by one of its Subsidiaries and such
         Lien and Acquired Debt were not incurred by the Company or any of its
         Subsidiaries or by the Person being acquired or from whom the assets
         were acquired in connection with, or in anticipation of, the incurrence
         of such Acquired Debt by the Company or by one of its Subsidiaries and
         (ii) any such Lien does not extend to or cover any property or assets
         of the Company or of any of its Subsidiaries other than the property or
         assets that secured the Acquired Debt prior to the time such Debt
         became Acquired Debt of the Company or of one of its Subsidiaries;

                  (6) Liens on Receivables securing Debt permitted by Section
         4.09(b)(8);

                  (7) Liens securing intercompany Debt permitted by Section
         4.09(b)(2);

                  (8) Liens securing the Credit Agreement, the New Credit
         Agreement and the Other Indebtedness (including Liens to be granted in
         connection with any Refinancing of the Credit Agreement, the New Credit
         Agreement and the Other Indebtedness);

                  (9) Liens permitted under the Credit Agreement or the New
         Credit Agreement as each such agreement was in effect on the effective
         date of the New Credit Agreement; and

                  (10) Beginning on the first anniversary of the effective date
         of the New Credit Agreement, Liens on assets of the Company and its
         Subsidiaries in addition to those referred to in clauses (1)-(9);


                                       7
<PAGE>   8

         provided that such Liens only secure Debt of the Company and its
         Subsidiaries in an aggregate amount not to exceed at any one time
         outstanding $30,000,000."

                  SECTION 1.06. (a) Section 4.13(6) of the Indenture is hereby
amended and restated in its entirety to read as follows:

                  "the Credit Agreement, the Receivables Financing Agreement,
                  other Debt existing on the Issue Date or the New Credit
                  Agreement; and"

                  (b) Section 4.13(7) of the Indenture is hereby amended and
restated in its entirety to read as follows:

                  "any Refinancing of the Credit Agreement, the Receivables
                  Financing Agreement, any such other Debt existing on the Issue
                  Date or the New Credit Agreement; provided that the terms and
                  conditions of any such Refinancing agreements relating to the
                  terms described under clauses (a)-(d) above are no less
                  favorable to the Company than those contained in the
                  agreements governing the Debt being Refinanced."

                  SECTION 1.07. A new Section 6.13 is hereby added to the
Indenture to read as follows:

                  "Notification to Collateral Agent. If an Event of Default
                  occurs and is continuing, the Trustee shall notify the
                  Collateral Agent (as defined in the Collateral Agent
                  Agreement) of such default pursuant to the terms of the
                  Collateral Agent Agreement and take any action as may be
                  required thereby."

                  SECTION 1.08. Section 9.01 of the Indenture is hereby amended
by adding a new paragraph (7) to read as follows:

                  "(7) to secure the Securities as contemplated by the first
                  paragraph of Section 4.11 hereof."

                                   ARTICLE II

                                   GUARANTEES

                  SECTION 2.01. Guarantee. Subject to Section 2.07, each
Guarantor, jointly and severally, hereby unconditionally and irrevocably
guarantees to each Holder (a "Guaranty"), the following obligations: (a) the
full and punctual payment of principal, premium, if any, and interest on the
Securities when due, whether at maturity, by acceleration, by redemption or
otherwise, and all other monetary obligations of the Company under the Indenture


                                       8
<PAGE>   9

and the Securities and (b) the full and punctual performance within applicable
grace periods of all other obligations of the Company under the Indenture
(including, without limitation, the compensation and other payment obligations
to the Trustee thereunder) and the Securities (all the foregoing being
hereinafter collectively called the "Guaranteed Obligations"). Each Guarantor
further agrees that the Guaranteed Obligations may be extended or renewed, in
whole or in part, without notice or further assent from such Guarantor and that
such Guarantor will remain bound under the terms hereof notwithstanding any
extension or renewal of any Guaranteed Obligation.

                  Each Guarantor agrees that its Guarantee herein constitutes a
guarantee of payment, performance and compliance when due (and not a guarantee
of collection) and waives any right to require that any resort be had by any
Holder or the Trustee to any security held for payment of the Guaranteed
Obligations.

                  The obligations of each Guarantor hereunder are independent of
the obligations of any other Guarantor, the Company, any Subsidiary thereof or
any other Person, and, subject to Section 2.05, a separate action or actions may
be brought and prosecuted against each Additional Guarantor whether or not
action is brought against any other Guarantor, the Company any Subsidiary
thereof or any other Person and whether or not any other Guarantor, the Company
or any Subsidiary thereof be joined in any such action or actions. Any payment
by the Company or any Subsidiary thereof or other circumstance which operates to
toll any statute of limitations as to the Company or any such Subsidiary shall
operate to toll the statute of limitations as to each Guarantor.

                  SECTION 2.02. Unconditional Obligations. This Guaranty shall
not be discharged except by complete performance of the Guaranteed Obligations
as contemplated in the Indenture and the Securities. The obligations of each
Guarantor hereunder shall not be affected by (a) the failure of any Holder or
the Trustee to assert any claim or demand or to enforce any right or remedy
against the Company or any other Person under the Indenture, the Securities or
any other agreement or otherwise; (b) any extension or renewal of any agreement
referred to in clause (a) of this paragraph; (c) any rescission, waiver,
amendment or modification of any of the terms or provisions of the Indenture,
the Securities or any other agreement; (d) the release of any security held by
or for the benefit of any Holder or the Trustee for the Guaranteed Obligations
or any of them; (e) the failure of any Holder or Trustee to exercise any right
or remedy against any other Guarantor of the Guaranteed Obligations or any other
Person; or (f) except as provided in Section 2.08 of this Second Supplemental
Indenture, any change in the ownership of such Guarantor. Each Guarantor hereby
waives notice of acceptance of this Guaranty and notice of any liability to
which it may apply, and waives promptness, diligence, presentment, demand of
payment, protest, notice of dishonor or any right to require a proceeding or the
taking of other action by the Trustee or any Holder against, and any other
notice to, any other Guarantor or the Company.

                  SECTION 2.03. Continuing Guaranty. This Guaranty is a
continuing one and all liabilities to which it applies or may apply under the
terms hereof shall be conclusively presumed to have been created in reliance


                                       9
<PAGE>   10

hereon. No failure or delay on the part of any Holder in exercising any right,
power or privilege hereunder shall operate as a waiver thereof, nor shall any
single or partial exercise of any right, power or privilege hereunder preclude
any other or further exercise thereof or the exercise of any other right, power
or privilege. The rights and remedies herein expressly specified are cumulative
and not exclusive of any rights or remedies which any Holder would otherwise
have. No notice to or demand on any Guarantor in any case shall entitle such
Guarantor to any other further notice or demand in similar or other
circumstances or constitute a waiver of the rights of any Holder to any other or
further action to any circumstances without notice or demand. It is not
necessary for any Holder to inquire into the capacity or powers of the Company
or any Subsidiary thereof or the officers, directors, partners or agents acting
or purporting to act on its behalf, and any indebtedness made or created in
reliance upon the professed exercise of such powers shall be guaranteed
hereunder.

                  SECTION 2.04. Subrogation; Acceleration. Each Guarantor agrees
that it shall not be entitled to any right of subrogation in respect of any
Guaranteed Obligations until payment in full of all Guaranteed Obligations. Each
Guarantor further agrees that, as between it, on the one hand, and the Holders
and the Trustee, on the other hand, (x) the maturity of the Guaranteed
Obligations may be accelerated as provided in Article VI of the Indenture for
the purposes of such Guarantor's Guarantee herein, notwithstanding any stay,
injunction or other prohibition preventing such acceleration in respect of the
Guaranteed Obligations, and (y) in the event of any declaration of acceleration
of such obligations as provided in Article VI of the Indenture, such Guaranteed
Obligations (whether or not due and payable) shall forthwith become due and
payable by each Guarantor for the purposes hereof.

                  SECTION 2.05. Enforcement. The Holders agree that this
Guaranty may be enforced only by the action of the Trustee in accordance with
the terms of the Indenture and that no other Holders shall have any right
individually to seek to enforce this Guaranty. The Holders further agree that
this Guaranty may not be enforced against any director, officer, employee, or
stockholder of any Guarantor (except to the extent such stockholder is also a
Guarantor hereunder).

                  SECTION 2.06. Covenants. Each Guarantor agrees that its
Guaranteed Obligations hereunder are senior Indebtedness of such Guarantor and
such Guaranteed Obligations shall not be subordinate to any existing or future
obligations of such Guarantor. Each Guarantor further covenants and agrees that
on and after the date hereof such Guarantor will comply (as a Recourse
Subsidiary of the Company), and will cause each of its Subsidiaries to comply,
with all of the applicable provisions, covenants and agreements contained in the
Indenture, and will take, or will refrain from taking, as the case may be, all
actions that are necessary to be taken or not taken so that it is not in
violation of any provision, covenant or agreement contained in the Indenture,
and so that no Default or Event of Default, is caused by the actions of such
Guarantor or any of its Subsidiaries.



                                       10
<PAGE>   11

         Each Guarantor hereby jointly and severally agrees to pay all
reasonable out-of-pocket costs and expenses of each Holder in connection with
the enforcement of this Guaranty and of the Trustee in connection with any
amendment, waiver or consent relating hereto (including in each case, without
limitation, the reasonable fees and disbursements of counsel employed by each
Holder).

                  SECTION 2.07. Limitation on Liability. Each Guarantor hereby
confirms that it is its intention that this Guaranty not constitute a fraudulent
transfer or conveyance for purposes of the Bankruptcy Law, the Uniform
Fraudulent Conveyance Act or any similar Federal or state law. Accordingly, each
Guarantor hereby irrevocably agrees that the Guaranteed Obligations guaranteed
by such Guarantor shall be limited to such amount as will, after giving effect
to such maximum amount and all other (contingent or otherwise) liabilities of
such Guarantor that are relevant under such laws, and after giving effect to any
rights to contribution pursuant to any agreement providing for an equitable
contribution among such Guarantor and the other Guarantors, result in the
Guaranteed Obligations of such Guarantor in respect of such maximum amount not
constituting a fraudulent transfer or conveyance

                  SECTION 2.08. Miscellaneous. (a) This Guaranty shall be
binding upon each Guarantor and its successors and assigns and shall inure to
the benefit of the Holders and their successors and assigns.

                  (b) Neither this Guaranty nor any provision hereof may be
changed, waived, discharged or terminated except with the written consent of
each Guarantor directly affected thereby and with the written consent of the
holders of a majority in aggregate principal amount of the Securities then
outstanding.

                  (c) All notices, requests, demands or other communications
pursuant hereto shall be made in accordance with Section 10.02 of the Indenture.

                  (d) In the event that all of the capital stock of one or more
Guarantors is sold or otherwise disposed of or liquidated in compliance with the
requirements of the Indenture and the proceeds of such sale, disposition or
liquidation are applied, to the extent applicable, in accordance with the
provisions of the Indenture, such Guarantor shall upon consummation of such sale
or other disposition (except to the extent that such sale or disposition is to
the Company or another Subsidiary thereof) be released from this Guaranty
automatically and without further action and this Guaranty shall, as to each
such Guarantor terminate, and have no further force or effect. At the request of
the Company, the Trustee shall execute and deliver an appropriate instrument
evidencing such release.

                                   ARTICLE III

                                  MISCELLANEOUS



                                       11
<PAGE>   12

                  SECTION 3.01. Effectiveness. This Second Supplemental
Indenture shall become effective immediately upon its execution and delivery by
the Issuer, the Guarantors and the Trustee, but Articles I and II shall not
become operative unless and until the Requisite Consents (as defined in the
Consent Solicitation Statement) are received and the New Credit Agreement and
the Credit Agreement become effective. In the event of any termination of the
Consent Solicitation set forth in the Consent Solicitation Statement or in the
event that Requisite Consents are not received, Articles I and II of this Second
Supplemental Indenture shall be null and void and of no force or effect.

                  SECTION 3.02. Confirmation. This Second Supplemental Indenture
and the Indenture shall henceforth be read together. Except as expressly set
forth herein, the Indenture shall remain unchanged and is in all respects
confirmed and preserved.

                  SECTION 3.03. Counterparts. This Second Supplemental Indenture
may be executed in counterparts, each of which shall be deemed an original, but
all of which together shall constitute one instrument.

                  SECTION 3.04. Governing Law. This Second Supplemental
Indenture shall be governed by the laws of the State of New York without regard
to the principles of conflicts of laws. The Trustee, the Issuer, the Guarantors
and the Holders agree to submit to the jurisdiction of the courts of the State
of New York in any action or proceeding arising out of or relating to the
Indenture or this Second Supplemental Indenture.







                                       12
<PAGE>   13

                  IN WITNESS WHEREOF, the parties hereto caused this Second
Supplemental Indenture to be signed and acknowledged by their respective
officers thereunto duly authorized as of the day and year first-above written.




             BUILDING MATERIALS CORPORATION OF AMERICA



             By: /s/ Susan B. Yoss
                ---------------------------------------------------
                        Name: Susan B. Yoss
                        Title: Senior Vice President and Treasurer



             BUILDING MATERIALS MANUFACTURING CORPORATION



             By: /s/ Susan B. Yoss
                ---------------------------------------------------
                        Name: Susan B. Yoss
                        Title: Senior Vice President and Treasurer



             BUILDING MATERIALS INVESTMENT CORPORATION

             By: /s/ Susan B. Yoss
                ---------------------------------------------------
                        Name: Susan B. Yoss
                        Title: Senior Vice President and Treasurer



             THE BANK OF NEW YORK,
             as Trustee

             By: /s/ Signature Illegible
                ---------------------------------------------------
                        Name:
                        Title:





                                       13
<PAGE>   14

             BMC WAREHOUSING INC.
             BMCA GOLDSBORO, INC.
             BMCA INSULATION PRODUCTS INC.
             DUCTWORK MANUFACTURING CORPORATION
             EXTERIOR TECHNOLOGIES CORPORATION
             GAF KALAMAZOO ACQUISITION CORP.
             GAF LEATHERBACK CORP.
             GAF MATERIALS CORPORATION (CANADA)
             GAF PREMIUM PRODUCTS INC.
             GAF REAL PROPERTIES, INC.
             GAFTECH CORPORATION
             INTEC MARINE INC.
             LL BUILDING PRODUCTS INC.
             PEQUANNOCK VALLEY CLAIM SERVICE COMPANY, INC.
             SOUTH PONCA REALTY CORP.
             TOPCOAT, INC.
             USI MATERIALS INC.
             U.S. INTEC, INC.
             US INTEC HOLDINGS INC.
             WIND GAP REAL PROPERTY ACQUISITION CORP.,
             as Additional Guarantors


             By: /s/ Susan B. Yoss
                ------------------------------------------------
                      Name: Susan B. Yoss
                      Title: Senior Vice President and Treasurer





                                       14