SIXTH AMENDMENT TO CREDIT AGREEMENT

Exhibit 10.24

SIXTH AMENDMENT TO CREDIT AGREEMENT

THIS SIXTH AMENDMENT TO CREDIT AGREEMENT (this “Amendment”) is dated as of and effective as of this 9^th day of November, 2006, by and between TREX COMPANY, INC., a Delaware corporation (sometimes hereinafter referred to herein as “Trex Inc.”), and BRANCH BANKING AND TRUST COMPANY OF VIRGINIA, a Virginia state banking corporation (hereinafter referred to herein as the “Bank”).

Trex Inc., TREX Company, LLC, a Delaware limited liability company (“TREX LLC”), and the Bank are the original parties to that certain Credit Agreement dated as of June 19, 2002, as amended by a First Amendment to Credit Agreement dated as of August 29, 2003, as further amended by a Second Amendment to Credit Agreement dated as of September 30, 2004, as further amended by a Third Amendment to Credit Agreement dated as of March 31, 2005, as further amended by a Fourth Amendment to Credit Agreement dated as of July 25, 2005, as further amended by a Fifth Amendment to Credit Agreement dated as of December 31, 2005 (as so amended and as it may hereafter be amended, restated, supplemented, replaced or otherwise modified from time to time, the “Credit Agreement”). Subject to the terms and conditions contained in the Credit Agreement, the Bank agreed to extend to Trex Inc. and TREX LLC (i) a revolving credit facility, with a letter of credit subfacility, in the aggregate amount of $30,000,000 for working capital financing of Trex Inc.’s and TREX LLC’s accounts receivable and inventory, to purchase new equipment and/or for other general corporate purposes of Trex Inc. and TREX LLC, (ii) a term loan facility in the amount of $9,570,079.88 to refinance the Winchester Property (as defined in the Credit Agreement), and (iii) a term loan facility in the amount of $3,029,920.12 to finance existing improvements to the Winchester Property. Effective December 31, 2002, TREX LLC merged with and into Trex Inc., with Trex Inc. being the surviving entity. As a result of such merger, Trex Inc. is the sole borrower under the Credit Agreement and shall hereinafter sometimes be referred to in this Amendment as the “Borrower.”

The Borrower has requested that the Bank increase the aggregate amount of the revolving credit facility for a specified period of time and make certain other modifications to the Credit Agreement, and the Bank is willing to do so upon the terms and conditions contained herein.

Accordingly, the Borrower and the Bank hereby agree as follows:

1. Capitalized terms used in this Amendment and not otherwise defined herein shall have the meanings assigned thereto in the Credit Agreement.

2. The first paragraph of Section 2.01(c)ii. of the Credit Agreement is hereby deleted in its entirety and the following paragraph is substituted in its place:

3. Section 6.01(c) of the Credit Agreement is hereby deleted in its entirety and the following Section is substituted in its place:

(c) Monthly Financial Statements. As soon as available and in any event within 15 Business Days after (i) the end of each month: (A) a Borrowing Base Certificate and (B) a financial report of accounts receivable (including an aging of accounts receivable in an initial increment of 30 days, a second increment of 31-45 days, a third increment of 46-60 days and in 30-day increments thereafter), inventory and production; and (ii) the end of the first two months of each fiscal quarter, an internally

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prepared consolidated and, with respect to Material Subsidiaries, consolidating balance sheet of the Borrower and its Consolidated Subsidiaries and the related consolidated and, with respect to Material Subsidiaries, consolidating statements of income and cash flows of the Borrower and its Consolidated Subsidiaries for such month all in reasonable detail and satisfactory in form to the Bank and all certified (subject to normal year-end audit adjustments) as to fairness of presentation, GAAP and consistency by the chief financial officer or chief accounting officer of the Borrower.

4. The second sentence of Section 6.06 of the Credit Agreement is hereby deleted in its entirety and the following two sentences are substituted in its place:

The Borrower shall pay to the Bank a borrowing base review fee in the amount of $500 on or before the first day of each calendar month commencing on December 1, 2006 and continuing to and including June 1, 2007. In addition, the costs of all field audits, inspections and appraisals will be borne by the Borrower; provided, however, that unless an Event of Default has occurred and is continuing, the Borrower shall only be responsible for the payment of one such audit, inspection or appraisal during each calendar year.

5. Section 6.07 of the Credit Agreement is hereby amended by inserting the following two (2) sentences at the end of that Section:

The Borrower hereby represents and warrants to the Bank that, as of November 9, 2006, neither the Borrower nor any of its Subsidiaries, nor any Corporate Assets, is subject to any agreement, judgment, injunction, order, decree or other instrument that prohibits, restricts or in any way limits the Borrower or any of its Subsidiaries from creating, incurring, assuming or suffering to exist any Lien upon or with respect to any Corporate Assets in favor of any creditor except for (i) the Loan Documents, (ii) agreements or documents creating or establishing Permitted Liens, (iii) the Note Agreement as amended as of November 9, 2006 and (iv) the Reimbursement and Credit Agreement dated as of December 1, 2004 by and between the Borrower, JPMorgan Chase Bank, N.A., as issuing bank, and JPMorgan Chase Bank, N.A., as administrative agent, as amended as of November 9, 2006 (as so amended, the “Chase Credit Agreement”). The Borrower hereby covenants and agrees that neither it nor any of its Subsidiaries, nor any of the Corporate Assets, will become subject to any agreement, judgment, injunction, order, decree or other instrument that prohibits, restricts or in any way limits the Borrower or any of its Subsidiaries from creating, incurring, assuming or suffering to exist any Lien upon or with respect to any of the Corporate Assets in favor of any creditor except for (i) the Loan Documents, (ii) agreements or documents creating or establishing Permitted Liens, (iii) the Note Agreement as amended as of November 9, 2006 and (iv) the Chase Credit Agreement.

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6. Section 6.11 of the Credit Agreement is hereby deleted in its entirety and the following Section is substituted in its place:

Section 6.11. Total Consolidated Debt to Consolidated EBITDA Ratio. The Borrower will not, as of the end of any fiscal quarter, permit the ratio of the Total Consolidated Debt to Consolidated EBITDA (the “Total Consolidated Debt to Consolidated EBITDA Ratio”) for the four-quarter period ended as of the end of such fiscal quarter to exceed the following amounts for the following periods: (i) 3.75 to 1 for the period commencing on October 1, 2006 to and including December 31, 2006, (ii) 3.25 to 1 for the period commencing on January 1, 2007 to and including March 31, 2007 and (iii) 2.50 to 1 thereafter.

7. The definition of the term, “Inventory Sublimit,” contained in the Definitions Appendix to the Credit Agreement is hereby deleted in its entirety and the following definition is substituted in its place:

“Inventory Sublimit” means (a) $10,000,000 for the period commencing on May 1, 2002 and continuing to and including September 30, 2002, (b) $12,000,000 for the period commencing on May 1, 2003 and continuing to and including September 30, 2003, (c) $14,000,000 for the period commencing on May 1, 2004 and continuing to and including September 30, 2004, (d) $16,000,000 for the period commencing on May 1, 2005 and continuing to and including September 30, 2005, (e) $16,000,000 for the period commencing on May 1, 2006 and continuing to and including September 30, 2006, (f) for any period occurring between May 1, 2002 to and including November 8, 2006 not identified in clauses (a) to and including (e) above, the Revolving Commitment, (g) $50,000,000 for the period commencing on November 9, 2006 and continuing to and including June 30, 2007, and (h) $15,000,000 for the period commencing on July 1, 2007 and at all times thereafter.

8. The definition of the term, “Revolving Commitment,” contained in the Definitions Appendix to the Credit Agreement is hereby deleted in its entirety and the following definition is substituted in its place:

“Revolving Commitment” means (i) for the period June 19, 2002 to and including December 31, 2005, $20,000,000.00 or such lesser amount to which it is reduced pursuant to Section 2.07, (ii) for the period January 1, 2006 to and including June 30, 2006, $30,000,000.00 or such lesser amount to which it is reduced pursuant to Section 2.07, (iii) for the period July 1, 2006 to and including November 8, 2006, $20,000,000.00 or such lesser amount to which it is reduced pursuant to Section 2.07, (iv) for the period November 9, 2006 to and including June 30, 2007, $70,000,000.00 or such lesser amount to which it is reduced pursuant to Section 2.07 and (v) for the period July 1, 2007 and at all times thereafter, $20,000,000 or such lesser amount to which it is reduced pursuant to Section 2.07.

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9. Exhibit I-3 to the Credit Agreement is hereby deleted in its entirety and a new Exhibit, which is attached to this Amendment and labeled Exhibit I-4, is substituted in its place.

10. The Borrower hereby represents and warrants to the Bank (which representations and warranties shall survive the execution and delivery of this Amendment) that:

(a) It is in compliance with all of the terms, covenants and conditions of the Credit Agreement, as amended by this Amendment, and each of the other Loan Documents.

(b) There exists no Default or Event of Default under the Credit Agreement, as amended by this Amendment, and no event has occurred or condition exists which, with the giving of notice or lapse of time, or both, would constitute such a Default or Event of Default.

(c) The representations and warranties contained in Article V of the Credit Agreement are, except to the extent that they relate solely to an earlier date or except to the extent that they relate solely to TREX LLC, true in all material respects with the same effect as though such representations and warranties had been made on the date of this Amendment.

(d) The execution, delivery and performance by the Borrower of this Amendment and the new promissory note (attached hereto as Exhibit I-4) are within its corporate powers, have been duly authorized by all necessary corporate action, require no action by or in respect of, or filing with, any governmental body, agency or official and do not contravene or constitute (with or without the giving of notice or lapse of time or both) a default under any provision of applicable law or of the organizational documents of the Borrower or any Subsidiary or of any agreement, judgment, injunction, order, decree or other instrument binding upon or affecting the Borrower or any Subsidiary or result in the creation or imposition of any Lien on any asset of the Borrower or any of its Subsidiaries.

(e) This Amendment and the promissory note described in paragraph 10(d) of this Amendment constitute the valid and binding agreements of the Borrower, enforceable against the Borrower in accordance with their respective terms, except as such enforceability may be limited by bankruptcy, insolvency or similar laws affecting creditors’ rights generally and by equitable principles of general applicability (regardless of whether such enforceability is considered in a proceeding in equity or at law).

(f) Except as set forth on Schedule 5.05 to the Credit Agreement, there is no material action, suit, proceeding or investigation pending against, or to the knowledge of the Borrower threatened against, contemplated or affecting, the Borrower or any of its Subsidiaries before any court, arbitrator or governmental body, agency or official which has, or could reasonably be expected to have, individually or in the aggregate, a Material Adverse Effect, or which in any manner draws into question the validity or

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enforceability of this Amendment, the promissory note described in paragraph 10(d) of this Amendment or any of the Loan Documents, and there is no basis known to the Borrower or any of its Subsidiaries for any such action, suit, proceeding or investigation.

11. The Bank’s agreement to enter into this Amendment is subject to the following conditions precedent:

(a) The Borrower shall have executed and delivered to the Bank this Amendment and the promissory note described in paragraph 10(d) of this Amendment in the form of Exhibit I-4 attached hereto with the blanks therein appropriately completed.

(b) The Borrower shall have executed and delivered, or caused to be executed and delivered, to the Bank such other and further documents, certificates, opinions and other papers as the Bank shall reasonably request; and the Borrower shall have paid all fees due to the Bank.

(c) The Bank shall have received a favorable opinion of counsel to the Borrower addressed to the Bank, dated as of the date hereof and satisfactory in form and substance to the Bank, as to the due authorization, execution, delivery and enforceability of this Amendment, the promissory note described in paragraph 10(d) of this Amendment, and such other matters as the Bank shall request.

(d) The Borrower shall have paid to the Bank in immediately available funds a modification fee in the amount of $50,000, which fee shall be deemed fully earned and non-refundable once paid.

12. Except as expressly amended hereby, the terms of the Credit Agreement shall remain in full force and effect in all respects, and the Borrower hereby reaffirms its obligations under the Credit Agreement, as amended by this Amendment, and each of the other Loan Documents. The Borrower hereby waives any claim, cause of action, defense, counterclaim, setoff or recoupment of any kind or nature that it may assert against the Bank arising from or in connection with the Credit Agreement, as amended by this Amendment, any of the Loan Documents, or the transactions contemplated thereby or hereby that exist on the date hereof or arise from facts or actions occurring prior hereto or on the date hereof. Nothing contained in this Amendment shall be construed to constitute a novation with respect to the obligations described in the Credit Agreement.

13. All references to the Credit Agreement in any of the Loan Documents, or any other documents or instruments that refer to the Credit Agreement, shall be deemed to be references to the Credit Agreement as amended by this Amendment.

14 This Amendment and the promissory note described in paragraph 10(d) of this Amendment shall be construed in accordance with and governed by the laws of the Commonwealth of Virginia.

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15. Any Dispute arising out of or related to this Amendment, the promissory note described in paragraph 10(d) of this Amendment or any of the Loan Documents shall be resolved by binding arbitration as provided in Section 9.07 of the Credit Agreement. TO THE FULLEST EXTENT PERMITTED BY LAW, THE PARTIES HERETO HEREBY IRREVOCABLY WAIVE THEIR RESPECTIVE RIGHTS TO A JURY TRIAL WITH RESPECT TO ANY DISPUTE.

16. This Amendment may be executed in any number of counterparts, each of which shall be an original, but all of which taken together shall constitute one and the same instrument.

17. This Amendment shall be binding upon and inure to the benefit of the parties hereto and their respective successors and assigns. The Borrower shall not have the right to assign any of its rights or obligations under or delegate any of its duties under the Credit Agreement, as amended by this Amendment, or any of the other Loan Documents.

18. The Borrower hereby agrees that it will pay on demand all out-of-pocket expenses incurred by the Bank in connection with the preparation of this Amendment and any other related documents, including but not limited to the fees and disbursements of counsel for the Bank.

19. This Amendment and the promissory note described in paragraph 10(d) of this Amendment represent the final agreement between the Borrower and the Bank with respect to the subject matter hereof, and may not be contradicted, modified or supplemented in any way by evidence of any prior or contemporaneous written or oral agreements of the Borrower and the Bank.

[Remainder of Page Intentionally Left Blank]

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IN WITNESS WHEREOF, the Borrower and the Bank have caused this Amendment to be executed by their duly authorized officers under seal as of the date first written above.

Exhibit I-4 - Promissory Note (Revolving Note)

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