<SEC-DOCUMENT>0001127602-25-005336.txt : 20250219
<SEC-HEADER>0001127602-25-005336.hdr.sgml : 20250219
<ACCEPTANCE-DATETIME>20250219075233
ACCESSION NUMBER:		0001127602-25-005336
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20250217
FILED AS OF DATE:		20250219
DATE AS OF CHANGE:		20250219

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Lovcik Brenda
		CENTRAL INDEX KEY:			0001998439
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-14649
		FILM NUMBER:		25637204

	MAIL ADDRESS:	
		STREET 1:		2500 TREX WAY
		STREET 2:		C/O TREX COMPANY, INC.
		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
		IRS NUMBER:				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>2025-02-17</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001998439</rptOwnerCik>
            <rptOwnerName>Lovcik Brenda</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, Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-02-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5957</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>67.33</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>21165</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-02-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>8510</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>67.33</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>29675</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Appreciation Right</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>67.33</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2025-02-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5133</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>67.33</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2026-03-01</value>
            </exerciseDate>
            <expirationDate>
                <value>2035-02-17</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5133</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8837</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This restricted stock unit award vests over a three-year period in three equal annual installments occurring March 1, 2026, March 1, 2027 and March 1, 2028.</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, 2026, March 1, 2027 and March 1, 2028. 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>
        <footnote id="F3">The stock appreciation right becomes exercisable in three equal installments occurring March 1, 2026, March 1, 2027 and March 1, 2028.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Amy M. Fernandez by power of attorney</signatureName>
        <signatureDate>2025-02-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
