Document:

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                           AINSWORTH LUMBER CO. LTD.,
                                    as Issuer
                                       and
                           AINSWORTH ENGINEERED CORP.
                             as Subsidiary Guarantor

             and THE BANK OF NOVA SCOTIA TRUST COMPANY OF NEW YORK,
                                   as Trustee

                             ---------------------

                          THIRD SUPPLEMENTAL INDENTURE

                         Dated as of September 22, 2004

                                     to the

                                    INDENTURE
                         Dated as of December 20, 2001,
              as supplemented by the First Supplemental Indenture,
                          dated as of February 27, 2004
                      and the Second Supplemental Indenture
                            dated as of May 19, 2004

                                     between

                           AINSWORTH LUMBER CO. LTD.,
                                   as Issuer,

                           AINSWORTH ENGINEERED CORP.
                             as Subsidiary Guarantor

                                       and

               THE BANK OF NOVA SCOTIA TRUST COMPANY OF NEW YORK,
                                   as Trustee

                             ---------------------

               13.875% Senior Secured Securities due July 15, 2007

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     THIRD SUPPLEMENTAL INDENTURE, dated as of September 22, 2004 (the "Third
Supplemental Indenture"), by and among Ainsworth Lumber Co. Ltd., a British
Columbia corporation (the "Issuer"), Ainsworth Engineered (USA), LLC, a Delaware
Limited Liability Corporation (the "Guaranteeing Subsidiary"), Ainsworth
Engineered Corp., a Nova Scotia Unlimited Liability Company (the "Prior
Guarantor") and The Bank of Nova Scotia Trust Company of New York, as Trustee
(the "Trustee").

     WHEREAS, the Issuer issued 13.875% Senior Secured Securities due July 15,
2007 (the "Securities") pursuant to the Indenture, dated as of December 20,
2001, among Ainsworth Lumber Co. Ltd. (as Issuer), Ainsworth Lumber Inc. (as
Subsidiary Guarantor) and The Bank of Nova Scotia Trust Company of New York (as
Trustee), as supplemented by the First Supplemental Indenture, dated as of
February 27, 2004 and the Second Supplemental Indenture, dated as of May 19,
2004 (as supplemented, the "Indenture"), which Securities have previously been
guaranteed by the Prior Guarantor pursuant to the provisions of the Indenture;

     WHEREAS, Steen River Forest Products Ltd., a former Guarantor under the
Indenture, was formally dissolved, effective March 3, 2004, and is no longer in
existence;

     WHEREAS, the Indenture provides that under certain circumstances a
Subsidiary providing a Subsidiary Guarantee shall execute and deliver to the
Trustee a supplemental indenture pursuant to which such Subsidiary shall
unconditionally guarantee all of the Company's Obligations under the Securities
and the Indenture (the "Subsidiary Guarantee");

     WHEREAS, pursuant to Section 901 of the Indenture, the Trustee is
authorized to execute and deliver this Third Supplemental Indenture; and

     WHEREAS, all things necessary to make this Third Supplemental Indenture a
valid supplement to the Indenture have been done.

     NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the parties
mutually covenant and agree for the equal and ratable benefit of the Holders of
the Securities as follows:

     SECTION 1. Certain Definitions. Unless otherwise stated, all capitalized
terms used but not defined herein shall have the meanings ascribed thereto in
the Indenture.

     SECTION 2. Agreement to Guarantee. The Guaranteeing Subsidiary hereby
agrees as follows:

     (a) Along with all Subsidiary Guarantors named in the Indenture, to jointly
and severally unconditionally guarantee to each Holder of a Security
authenticated and delivered by the Trustee and to the Trustee and its successors
and assigns,

                                      S-1
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irrespective of the validity and enforceability of the Indenture,
the Securities or the obligations of the Company hereunder or thereunder, that:

          (i) the principal of and interest and premium, if any, on the
          Securities will be promptly paid in full when due, whether at
          maturity, by acceleration, redemption or otherwise, according to the
          terms thereof and of the Indenture; and

          (ii) in case of failure by the Company to punctually pay the principal
          of and interest and premium, if any, on the Securities when due,
          whether at stated maturity, by acceleration or otherwise, the
          Subsidiary Guarantors shall be jointly and severally obligated to pay
          the same immediately.

     (b) The Guaranteeing Subsidiary will be subject to all the provisions of
the Indenture applicable to a Subsidiary Guarantor.

     (c) The obligations hereunder shall be absolute and unconditional,
irrespective of and shall be unaffected by the validity, regularity or
enforceability of the Securities or the Indenture, the absence of any action to
enforce the same, any release, amendment, waiver or indulgence granted to the
Company or any other guarantor, or any consent to departure from any requirement
of any other guarantee of all or of any of the Securities, or any other
circumstances which might otherwise constitute a legal or equitable discharge or
defense of a surety or guarantor; provided, however, that, notwithstanding the
foregoing, no such release, amendment, waiver or indulgence shall, without the
consent of the Guaranteeing Subsidiary, increase the principal amount of the
Securities, or increase the interest rate thereon, or alter the Stated Maturity
thereof.

     (d) If, after the occurrence and during the continuance of an Event of
Default, the Trustee or any of the Holders are prevented by applicable law from
exercising their respective rights to accelerate the maturity of the Securities,
to collect interest on the Securities, or to enforce or exercise any other right
or remedy with respect to the Securities, the Guaranteeing Subsidiary shall pay
to the Trustee for the account of the Holders, upon demand therefor, the amount
that would otherwise have been due and payable had such rights and remedies been
permitted to be exercised by the Trustee or any of the Holders.

     (e) The following is hereby waived: diligence, presentment, demand for
payment, any requirement that the Trustee or any of the Holders protect, secure,
perfect or insure any security interest in or other Lien on any property subject
thereto or exhaust any right or take any action against the Company or any other
Person or any collateral, filing of claims with a court in the event of
insolvency or bankruptcy of the Company, any right to require a proceeding first
against the Company, protest or notice with respect to the Securities, the
indebtedness evidenced thereby, the Indenture and this Supplemental Indenture
and all demands whatsoever.

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     (f) This Subsidiary Guarantee shall not be discharged except by complete
performance of the obligations contained in the Securities, the Indenture and
this Supplemental Indenture, and the Guaranteeing Subsidiary accepts all
obligations of a Subsidiary Guarantor under the Indenture.

     (g) The Guaranteeing Subsidiary shall be subrogated to all rights of the
Holders of the Securities against the Company in respect of any amounts paid by
the Guaranteeing Subsidiary on account of the Securities pursuant to the
provisions of the Subsidiary Guarantee or the Indenture, as supplemented by this
Supplemental Indenture; provided, however, that the Guaranteeing Subsidiary
shall not be entitled to enforce or to receive any payments arising out of, or
based upon, such right of subrogation until the principal of (and premium, if
any) and interest on the Securities shall have been paid in full.

     (h) The Guaranteeing Subsidiary shall, to the extent that it makes or is
required to make any payment in respect of this Subsidiary Guarantee, be
entitled to seek contribution from the other Subsidiary Guarantors to the extent
permitted by applicable law; provided, however, that the Guaranteeing Subsidiary
shall not be entitled to enforce or receive any payments arising out of, or
based upon, such right of contribution until the principal of (and premium, if
any) and interest on all Securities issued under the Indenture shall have been
paid in full.

     (i) This Subsidiary Guarantee shall remain in full force and effect and
continue to be effective should any petition be filed by or against the Company
for liquidation or reorganization, should the Company become insolvent or make
an assignment for the benefit of creditors or should a receiver or trustee be
appointed for all or any significant part of the Company's assets, and shall, to
the fullest extent permitted by law, continue to be effective or be reinstated,
as the case may be, if at any time payment and performance of the Securities
are, pursuant to applicable law, rescinded or reduced in amount, or must
otherwise be restored or returned by any Holder of the Securities, whether as a
"voidable preference", "fraudulent transfer" or otherwise, all as though such
payment or performance had not been made. In the event that any payment or any
part thereof, is rescinded, reduced, restored or returned, the Security shall,
to the fullest extent permitted by law, be reinstated and deemed reduced only by
such amount paid and not so rescinded, reduced, restored or returned.

     (j) In case any provision of this Subsidiary Guarantee shall be invalid,
illegal or unenforceable, the validity, legality, and enforceability of the
remaining provisions shall not in any way be affected or impaired thereby.

     (k) This Subsidiary Guarantee shall be a general unsecured obligation of
such Guaranteeing Subsidiary, ranking pari passu with any other future senior
Indebtedness of the Guaranteeing Subsidiary, if any.

     (l) Each payment to be made by the Guaranteeing Subsidiary in respect of
this Subsidiary Guarantee shall be made without set-off, counterclaim, reduction
or diminution of any kind or nature.

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     SECTION 3. Execution and Delivery. The Guaranteeing Subsidiary agrees that,
subject to Section 1203 of the Indenture, this Subsidiary Guarantee shall remain
in full force and effect until the entire principal of, premium, if any, and
interest on the Securities shall have been paid in full or otherwise discharged
in accordance with the provisions of the Securities and the Indenture and all
amounts owing to the Trustee under the Indenture have been paid, notwithstanding
any failure to endorse on each Security a notation of this Subsidiary Guarantee.

     SECTION 4. Releases. Notwithstanding Section 3 above, if:

          (i) the Subsidiary Guarantor ceases to be a Restricted Subsidiary in
          compliance with the applicable provisions of the Indenture;

          (ii) the Securities are defeased and discharged pursuant to Section
          1502 of the Indenture; or

          (iii) all or substantially all of the assets of the Guaranteeing
          Subsidiary or all of the Capital Stock of the Guaranteeing Subsidiary
          are sold (including by issuance, amalgamation, merger, consolidation
          or otherwise) by the Company or any Restricted Subsidiary in a
          transaction constituting an Asset Disposition and in which the Net
          Available Proceeds from such Assets Disposition are applied in
          accordance with requirements of Section 1013 of the Indenture,

     then, in each case of (i), (ii) or (iii), upon delivery by the Company of
an Officers' Certificate and an Opinion of Counsel stating that all conditions
precedent contained in the Indenture provided for relating to the release of the
Guaranteeing Subsidiary from its obligations under the Subsidiary Guarantee and
Article Twelve of the Indenture have been complied with, the Guaranteeing
Subsidiary or the Person acquiring such assets (in the event of a sale or other
disposition of all or substantially all of the assets or Capital Stock of such
Guaranteeing Subsidiary) shall be released and discharged of its obligations
under the Subsidiary Guarantee and under Article Twelve of the Indenture without
any action on the part of the Trustee or any Holder, and the Trustee shall
execute any documents reasonably required in order to acknowledge the release of
the Guaranteeing Subsidiary from its obligations under this Subsidiary Guarantee
endorsed on the Securities and under this Subsidiary Guarantee and Article
Twelve of the Indenture.

     SECTION 5. No Recourse Against Others. No past, present or future director,
officer, employee, incorporator, shareholder or agent of the Guaranteeing
Subsidiary, as such, shall have any liability for any obligations of the Company
or any Subsidiary under the Securities, any Subsidiary Guarantees, the Indenture
or this Supplemental Indenture or for any claim based on, in respect of, or by
reason of, such obligations or their creation. Each Holder of the Securities by
accepting a Security waives and releases all such liability. The waiver and
release are part of the consideration for the issuance of the Securities. Such
waiver may not be effective to

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waive liabilities under the federal securities laws and it is the view of the
Commission that such a waiver is against public policy.

     SECTION 6. Governing Law. This Third Supplemental Indenture shall be
governed by and construed in accordance with the laws of the State of New York,
as applied to contracts made and performed within the State of New York.

     SECTION 7. Counterparts. This Third Supplemental Indenture may be signed in
any number of counterparts, each of which shall be an original, with the same
effect as if the signatures thereto and hereto were upon the same instrument.

     SECTION 8. Severability. In case any provision in this Third Supplemental
Indenture shall be invalid, illegal or unenforceable, the validity, legality and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby.

     SECTION 9. Ratification. Except as expressly amended hereby, each provision
of the Indenture shall remain in full force and effect and, as amended hereby,
the Indenture is in all respects agreed to, ratified and confirmed by each of
the Issuer, the Prior Guarantor, the Guaranteeing Subsidiary and the Trustee.

     SECTION 10. Trustee Makes No Representation. The Trustee makes no
representation as to the validity or sufficiency of this Third Supplemental
Indenture. The statements and recitals herein are deemed to be those of the
Issuer and the Guaranteeing Subsidiary and not of the Trustee.

     SECTION 11. Successors and Assigns. All covenants and agreements in this
Third Supplemental Indenture by the Issuer, the Prior Guarantor, the
Guaranteeing Subsidiary, the Trustee and the Holders shall bind their respective
successors and assigns, whether so expressed or not.

     SECTION 12. Effect of Headings. The Section headings herein are for
convenience only and shall not effect the construction hereof.

                                      S-5
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     IN WITNESS WHEREOF, the parties hereto have caused this Third Supplemental
Indenture to be duly executed as of the date first above written.

                                    AINSWORTH LUMBER CO. LTD.,
                                    as Issuer

                                    By:    /s/ Catherine Ainsworth
                                           -------------------------------------
                                           Catherine Ainsworth
                                           Chief Operating Officer

                                    AINSWORTH ENGINEERED CORP.,
                                    as Subsidiary Guarantor

                                    By:    /s/ Catherine Ainsworth
                                           -------------------------------------
                                           Catherine Ainsworth
                                           Secretary

                                    AINSWORTH ENGINEERED (USA), LLC
                                    as Subsidiary Guarantor

                                    By:    /s/ Catherine Ainsworth
                                           -------------------------------------
                                           Catherine Ainsworth
                                           Secretary

                                    THE BANK OF NOVA SCOTIA TRUST
                                    COMPANY OF NEW YORK,
                                    as Trustee

                                    By:
                                           -------------------------------------
                                           Name:  Warren Goshine
                                           Title:  Vice President

                                      S-6<PAGE>

     SECOND SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated as of
September 22, 2004, among Ainsworth Engineered (USA), LLC (the "Guaranteeing
Subsidiary"), a subsidiary of Ainsworth Lumber Co. Ltd., a corporation
incorporated under the laws of the Province of British Columbia (the "Company"),
the Company, Ainsworth Engineered Corp., a subsidiary of the Company (the "Prior
Guarantor") and The Bank of New York, as Trustee under the Indenture referred to
below (the "Trustee").

                               W I T N E S S E T H

     WHEREAS, the Company has heretofore executed and delivered to the Trustee
an indenture (the "Indenture"), dated as of May 19, 2004 providing for the
issuance of an unlimited aggregate principal amount of Senior Notes due March
15, 2014 (the "Notes"), as supplemented by the First Supplemental Indenture,
dated as of May 19, 2004 among the Prior Guarantor, the Company and the Trustee
(as supplemented, the "Indenture");

     WHEREAS, the Indenture provides that under certain circumstances a
Subsidiary providing a Subsidiary Guarantee shall execute and deliver to the
Trustee a supplemental indenture pursuant to which such Subsidiary shall
unconditionally guarantee all of the Company's Obligations under the Notes and
the Indenture on the terms and conditions set forth herein (the "Subsidiary
Guarantee"); and

     WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee is
authorized to execute and deliver this Supplemental Indenture.

     NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the parties
mutually covenant and agree for the equal and ratable benefit of the Holders of
the Notes as follows:

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

     2. AGREEMENT TO GUARANTEE. The Guaranteeing Subsidiary hereby agrees as
follows:

          (a) Along with all Guarantors named in the Indenture, to jointly and
     severally unconditionally guarantee to each Holder of a Note authenticated
     and delivered by the Trustee and to the Trustee and its successors and
     assigns, irrespective of the validity and enforceability of the Indenture,
     the Notes or the obligations of the Company hereunder or thereunder, that:

               (i) the principal of and interest, premium and Special Interest,
          if any, on the Notes will be promptly paid in full when due, whether
          at maturity, by acceleration, redemption or otherwise, and interest on
          the overdue principal of and interest on the Notes, if any, if lawful,

<PAGE>

          and all other obligations of the Company to the Holders or the Trustee
          hereunder or thereunder will be promptly paid in full or performed,
          all in accordance with the terms hereof and thereof; and

               (ii) in case of any extension of time of payment or renewal of
          any Notes or any of such other obligations, that same will be promptly
          paid in full when due or performed in accordance with the terms of the
          extension or renewal, whether at stated maturity, by acceleration or
          otherwise. Failing payment when due of any amount so guaranteed or any
          performance so guaranteed for whatever reason, the Guarantors shall be
          jointly and severally obligated to pay the same immediately.

          (b) The obligations hereunder shall be unconditional, irrespective of
     the validity, regularity or enforceability of the Notes or the Indenture,
     the absence of any action to enforce the same, any waiver or consent by any
     Holder of the Notes with respect to any provisions hereof or thereof, the
     recovery of any judgment against the Company, any action to enforce the
     same or any other circumstance which might otherwise constitute a legal or
     equitable discharge or defense of a guarantor.

          (c) The obligations of the Guaranteeing Subsidiary under this
     Subsidiary Guarantee are independent of the obligations guaranteed by the
     Guaranteeing Subsidiary hereunder, and a separate action or actions may be
     brought and prosecuted by the Trustee on behalf of, or by, the Holders,
     subject to the terms and conditions set forth in the Indenture, against the
     Guaranteeing Subsidiary to enforce this Subsidiary Guarantee, irrespective
     of whether any action is brought against the Company or whether the Company
     is joined in any such action or actions.

          (d) In the event of a default in payment of principal (or premium and
     Special Interest, if any) or interest on a Note, whether at its stated
     maturity, by acceleration, purchase or otherwise, legal proceedings may be
     instituted by the Trustee on behalf of, or by, the Holder of such Note,
     subject to the terms and conditions set forth in the Indenture, directly
     against the Guaranteeing Subsidiary to enforce the Subsidiary Guarantee
     without first proceeding against the Company or any other Guarantor. If,
     after the occurrence and during the continuance of an Event of Default, the
     Trustee or any of the Holders are prevented by applicable law from
     exercising their respective rights to accelerate the maturity of the Notes,
     to collect interest on the Notes, or to enforce or exercise any other right
     or remedy with respect to the Notes, the Guaranteeing Subsidiary shall pay
     to the Trustee for the account of the Holder, upon demand therefor, the
     amount that would otherwise have been due and payable had such rights and
     remedies been permitted to be exercised by the Trustee or any of the
     Holders.

          (e) The following is hereby waived: diligence presentment, demand of
     payment, filing of claims with a court in the event of insolvency or
     bankruptcy of

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     the Company, any right to require a proceeding first against the Company,
     protest, notice and all demands whatsoever.

          (f) This Subsidiary Guarantee shall not be discharged except by
     complete performance of the obligations contained in the Notes, the
     Indenture and this Supplemental Indenture, and the Guaranteeing Subsidiary
     accepts all obligations of a Guarantor under the Indenture.

          (g) If any Holder or the Trustee is required by any court or otherwise
     to return to the Company, the Guarantors (including the Guaranteeing
     Subsidiary), or any custodian, trustee, liquidator or other similar
     official acting in relation to either the Company or the Guarantors, any
     amount paid either to the Trustee or such Holder, this Subsidiary
     Guarantee, to the extent theretofore discharged, shall be reinstated in
     full force and effect.

          (h) The Guaranteeing Subsidiary shall not be entitled to any right of
     subrogation in relation to the Holders in respect of any obligations
     guaranteed hereby until payment in full of all obligations guaranteed
     hereby.

          (i) As between the Guaranteeing Subsidiary, on the one hand, and the
     Holders and the Trustee, on the other hand, (x) the maturity of the
     obligations guaranteed hereby may be accelerated as provided in Article 6
     of the Indenture for the purposes of this Subsidiary Guarantee,
     notwithstanding any stay, injunction or other prohibition preventing such
     acceleration in respect of the obligations guaranteed hereby, and (y) in
     the event of any declaration of acceleration of such obligations as
     provided in Article 6 of the Indenture, such obligations (whether or not
     due and payable) shall forthwith become due and payable by the Guaranteeing
     Subsidiary for the purpose of this Subsidiary Guarantee.

          (j) The Guaranteeing Subsidiary shall have the right to seek
     contribution from any non-paying Guarantor so long as the exercise of such
     right does not impair the rights of the Holders under this Subsidiary
     Guarantee.

          (k) Pursuant to Section 10.02 of the Indenture, after giving effect to
     all other contingent and fixed liabilities that are relevant under any
     applicable Bankruptcy or fraudulent conveyance laws, and after giving
     effect to any collections from, rights to receive contribution from or
     payments made by or on behalf of any other Guarantor in respect of the
     obligations of such other Guarantor under Article 10 of the Indenture, this
     new Subsidiary Guarantee shall be limited to the maximum amount permissible
     such that the obligations of such Guaranteeing Subsidiary under this
     Subsidiary Guarantee will not constitute a fraudulent transfer or
     conveyance.

          (l) This Subsidiary Guarantee shall remain in full force and effect
     and continue to be effective should any petition be filed by or against the
     Company for liquidation, reorganization, should the Company become
     insolvent or make an

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     assignment for the benefit of creditors or should a receiver or trustee be
     appointed for all or any significant part of the Company's assets, and
     shall, to the fullest extent permitted by law, continue to be effective or
     be reinstated, as the case may be, if at any time payment and performance
     of the Notes are, pursuant to applicable law, rescinded or reduced in
     amount, or must otherwise be restored or returned by any obligee on the
     Notes and Subsidiary Guarantee, whether as a "voidable preference",
     "fraudulent transfer" or otherwise, all as though such payment or
     performance had not been made. In the event that any payment or any part
     thereof, is rescinded, reduced, restored or returned, the Note shall, to
     the fullest extent permitted by law, be reinstated and deemed reduced only
     by such amount paid and not so rescinded, reduced, restored or returned.

          (m) In case any provision of this Subsidiary Guarantee shall be
     invalid, illegal or unenforceable, the validity, legality, and
     enforceability of the remaining provisions shall not in any way be affected
     or impaired thereby.

          (n) This Subsidiary Guarantee shall be a general unsecured obligation
     of such Guaranteeing Subsidiary, ranking pari passu with any other future
     senior Indebtedness of the Guaranteeing Subsidiary, if any.

          (o) Each payment to be made by the Guaranteeing Subsidiary in respect
     of this Subsidiary Guarantee shall be made without set-off, counterclaim,
     reduction or diminution of any kind or nature.

     3. EXECUTION AND DELIVERY. The Guaranteeing Subsidiary agrees that the
Subsidiary Guarantee shall remain in full force and effect notwithstanding any
failure to endorse on each Note a notation of this Subsidiary Guarantee.

     4. GUARANTEEING SUBSIDIARY MAY CONSOLIDATE, ETC. ON CERTAIN TERMS.

          (a) Except as otherwise provided in Section 10.05 of the Indenture,
     the Guaranteeing Subsidiary may not sell or otherwise dispose of all or
     substantially all of its assets to, or consolidate, amalgamate with or
     merge with or into (whether or not such Guaranteeing Subsidiary is the
     surviving Person) another Person other than the Company or another
     Guarantor unless:

          (b) immediately after giving effect to that transaction, no Default or
     Event of Default exists; and

          (c) either:

               (1) the Guaranteeing Subsidiary is the surviving Person, or the
          Person acquiring the property in any such sale or disposition or the
          Person formed by or surviving any such consolidation, amalgamation or
          merger assumes all the obligations of the Guaranteeing Subsidiary
          under the Indenture, this Subsidiary Guarantee and the Registration
          Rights Agreement pursuant to a supplemental indenture satisfactory to
          the Trustee and completes all other required documentation; or

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               (2) the Net Proceeds of such sale or other disposition are
          applied in accordance with the provisions of Section 4.10 of the
          Indenture;

          (d) In case of any such consolidation, amalgamation, merger, sale or
     conveyance and upon the assumption by the successor Person (where
     applicable), by supplemental indenture, executed and delivered to the
     Trustee and satisfactory in form to the Trustee, of this Subsidiary
     Guarantee endorsed upon the Notes and the due and punctual performance of
     all of the covenants and conditions of the Indenture to be performed by the
     Guaranteeing Subsidiary, such successor Person shall succeed to and be
     substituted for the Guaranteeing Subsidiary with the same effect as if it
     had been named herein as a Guaranteeing Subsidiary. Such successor Person
     thereupon may cause to be signed the Subsidiary Guarantee to be endorsed
     upon all of the Notes issuable hereunder which theretofore shall not have
     been signed by the Company and delivered to the Trustee. The Subsidiary
     Guarantee so issued shall in all respects have the same legal rank and
     benefit under the Indenture as the Subsidiary Guarantees theretofore and
     thereafter issued in accordance with the terms of the Indenture as though
     all of such Subsidiary Guarantees had been issued at the date of the
     execution hereof.

          (e) Except as set forth in Articles 4 and 5 of the Indenture, and
     notwithstanding clauses (a) and (b) above, nothing contained in the
     Indenture or in any of the Notes shall prevent any consolidation,
     amalgamation or merger of a Guaranteeing Subsidiary with or into the
     Company or another Guarantor, or shall prevent any sale or conveyance of
     the property of the Guaranteeing Subsidiary as an entirety or substantially
     as an entirety to the Company or another Guarantor.

     5. RELEASES.

          (a) In the event of a sale (including by way of merger, amalgamation
     or consolidation in compliance with Section 5.01 of the Indenture) of all
     the capital stock of the Guaranteeing Subsidiary to a Person that is not
     (either before or after giving effect to such transaction) the Company or a
     Restricted Subsidiary then the Guaranteeing Subsidiary (in the event of a
     sale or other disposition, by way of merger, consolidation or otherwise, of
     all of the capital stock of such Guaranteeing Subsidiary) will be released
     and relieved of any obligations under this Subsidiary Guarantee; provided,
     that the sale complies with Section 4.10 of the Indenture. Further, if the
     Company redesignates any Restricted Subsidiary that is a Guarantor as an
     Unrestricted Subsidiary in accordance with Section 4.17 of the Indenture
     then the Guaranteeing Subsidiary will be released and relieved of any
     obligations under this Subsidiary Guarantee. Upon delivery by the Company
     to the Trustee of an Officers' Certificate and an Opinion of Counsel to the
     effect that such sale or other disposition was made by the Company in
     accordance with the provisions of the Indenture, including without
     limitation Section 4.10 of the Indenture, the Trustee shall execute any
     documents reasonably required in order to evidence the release of the
     Guaranteeing Subsidiary from its obligations under this Subsidiary
     Guarantee.

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          (b) The Guaranteeing Subsidiary not released from its obligations
     under this Subsidiary Guarantee shall remain liable for the full amount of
     principal of and interest on the Notes and for the other obligations of the
     Guaranteeing Subsidiary under the Indenture as provided in Article 10
     thereof.

     6. NO RECOURSE AGAINST OTHERS. No past, present or future director,
officer, employee, incorporator, shareholder or agent of the Guaranteeing
Subsidiary, as such, shall have any liability for any obligations of the Company
or any Subsidiary under the Notes, any Subsidiary Guarantees, the Indenture or
this Supplemental Indenture or for any claim based on, in respect of, or by
reason of, such obligations or their creation. Each Holder of the Notes by
accepting a Note waives and releases all such liability. The waiver and release
are part of the consideration for the issuance of the Notes. Such waiver may not
be effective to waive liabilities under the federal securities laws and it is
the view of the Commission that such a waiver is against public policy.

     7. THE LAWS OF THE STATE OF NEW YORK SHALL GOVERN AND BE USED TO CONSTRUE
THIS SUPPLEMENTAL INDENTURE, THE INDENTURE, THE NOTES AND THE SUBSIDIARY
GUARANTEES.

     8. COUNTERPARTS. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

     9. EFFECT OF HEADINGS. The Section headings herein are for convenience only
and shall not affect the construction hereof.

     10. THE TRUSTEE. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made solely by the Guaranteeing Subsidiary and the Company.

     11. SUBROGATION. The Guaranteeing Subsidiary shall be subrogated to all
rights of Holders of Notes against the Company in respect of any amounts paid by
the Guaranteeing Subsidiary pursuant to the provisions of Section 2 hereof;
provided, however, that, if an Event of Default has occurred and is continuing,
the Guaranteeing Subsidiary shall not be entitled to enforce or receive any
payments arising out of, or based upon, such right of subrogation until all
amounts then due and payable by the Company under the Indenture or the Notes
shall have been paid in full.

     12. BENEFITS ACKNOWLEDGED. The Guaranteeing Subsidiary acknowledges that it
will receive direct and indirect benefits from the financing arrangements
contemplated by the Indenture and this Supplemental Indenture and that the
guarantee and waivers made by it pursuant to this Subsidiary Guarantee are
knowingly made in contemplation of such benefits.

     13. SUCCESSORS. All agreements of the Guaranteeing Subsidiary in this
Supplemental Indenture shall bind its Successors, except as otherwise provided
in Section

                                       6
<PAGE>

2(k) hereof or elsewhere in this Supplemental Indenture. All agreements of the
Trustee in this Supplemental Indenture shall bind its successors.

                                       7
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed, all as of the date first above written.

                                      Ainsworth Lumber Co. Ltd.

                                      By:    /s/ Catherine Ainsworth
                                             -----------------------------------
                                             Name:  Catherine Ainsworth
                                             Title:  Chief Operating Officer

                                      By:    /s/ Michael Ainsworth
                                             -----------------------------------
                                             Name:  Michael Ainsworth
                                             Title:  Executive Vice-President

                                      Ainsworth Engineered Corp.

                                      By:    /s/ Catherine Ainsworth
                                             -----------------------------------
                                             Name:  Catherine Ainsworth
                                             Title:  Secretary

                                      Ainsworth Engineered (USA), LLC

                                      By:    /s/ Catherine Ainsworth
                                             -----------------------------------
                                             Name:  Catherine Ainsworth
                                             Title:  Secretary

                                      The Bank of New York, as Trustee

                                      By:    /s/ Patricia Phillips-Coward
                                             -----------------------------------
                                             Authorized Signatory

                                       8

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