<SEC-DOCUMENT>0001069878-26-000020.txt : 20260225
<SEC-HEADER>0001069878-26-000020.hdr.sgml : 20260225
<ACCEPTANCE-DATETIME>20260225210008
ACCESSION NUMBER:		0001069878-26-000020
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20260224
FILED AS OF DATE:		20260225
DATE AS OF CHANGE:		20260225

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Fernandez Amy M.
		CENTRAL INDEX KEY:			0001987902
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-14649
		FILM NUMBER:		26681300

	MAIL ADDRESS:	
		STREET 1:		2500 TREX WAY
		CITY:			WINCHESTER
		STATE:			VA
		ZIP:			22601

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			TREX CO INC
		CENTRAL INDEX KEY:			0001069878
		STANDARD INDUSTRIAL CLASSIFICATION:	LUMBER & WOOD PRODUCTS (NO FURNITURE) [2400]
		ORGANIZATION NAME:           	04 Manufacturing
		EIN:				541910453
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		2500 TREX WAY
		CITY:			WINCHESTER
		STATE:			VA
		ZIP:			22601
		BUSINESS PHONE:		5405426300

	MAIL ADDRESS:	
		STREET 1:		2500 TREX WAY
		CITY:			WINCHESTER
		STATE:			VA
		ZIP:			22601
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>form4.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2026-02-24</periodOfReport>

    <issuer>
        <issuerCik>0001069878</issuerCik>
        <issuerName>TREX CO INC</issuerName>
        <issuerTradingSymbol>TREX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001987902</rptOwnerCik>
            <rptOwnerName>Fernandez Amy M.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TREX COMPANY, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>2500 TREX WAY</rptOwnerStreet2>
            <rptOwnerCity>WINCHESTER</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>22601</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>SVP, CLO and Secretary</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-02-24</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>10181</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>41.45</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>62332</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-02-24</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>10181</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>41.45</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>72513</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">This restricted stock unit award vests over a three-year period in three equal annual installments occurring March 1, 2027, March 1, 2028, and March 1, 2029.</footnote>
        <footnote id="F2">This restricted stock unit award is performance-based, and vests over a three-year period in three equal installments occurring March 1, 2027, March 1, 2028, and March 1, 2029. The number of shares set forth above is the target number of shares. The number of shares that will actually vest each year will be based upon performance against certain financial goals for the Company and will range from 0% to 200% of the target number of shares.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Amy M. Fernandez</signatureName>
        <signatureDate>2026-02-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
