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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 DvdVKCfCR6sD/FEJ6I9fKpl425dBc2ykfpTwvdOd0jMk0PhYlzzxyNl1mCOnAnTx
 LnPRycKvxsAsIu0K8wiSDg==

<SEC-DOCUMENT>0001264385-05-000142.txt : 20050803
<SEC-HEADER>0001264385-05-000142.hdr.sgml : 20050803
<ACCEPTANCE-DATETIME>20050803101317
ACCESSION NUMBER:		0001264385-05-000142
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050802
FILED AS OF DATE:		20050803
DATE AS OF CHANGE:		20050803

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			LAFARGE NORTH AMERICA INC
		CENTRAL INDEX KEY:			0000716783
		STANDARD INDUSTRIAL CLASSIFICATION:	CEMENT, HYDRAULIC [3241]
		IRS NUMBER:				581290226
		STATE OF INCORPORATION:			MD
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		12950 WORLDGATE DR. SUITE 500
		CITY:			HERNDON
		STATE:			VA
		ZIP:			20170
		BUSINESS PHONE:		7034803600

	MAIL ADDRESS:	
		STREET 1:		12950 WORLDGATE DR. SUITE 500
		CITY:			HERNDON
		STATE:			VA
		ZIP:			20170

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			COHEN MARSHALL A
		CENTRAL INDEX KEY:			0001174913

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-08584
		FILM NUMBER:		05994082

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		2036987500

	MAIL ADDRESS:	
		STREET 1:		1700 E PUTNAM AVE
		STREET 2:		SUITE 400
		CITY:			OLD GREENWICH
		STATE:			CT
		ZIP:			06870
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-08-02</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000716783</issuerCik>
        <issuerName>LAFARGE NORTH AMERICA INC</issuerName>
        <issuerTradingSymbol>LAF</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001174913</rptOwnerCik>
            <rptOwnerName>COHEN MARSHALL A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1700 E PUTNAM AVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 400</rptOwnerStreet2>
            <rptOwnerCity>OLD GREENWICH</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06870</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-08-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>462</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>69.78</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>462</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4725</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">These shares are payable on a 1 for 1 basis.</footnote>
        <footnote id="F2">The shares of phantom stock become payable in cash or common stock, at the election of the reporting person, upon the reporting person's termination of service as a director.</footnote>
        <footnote id="F3">Includes shares received upon payment of quarterly dividends.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>William G. Miller, signed pursuant to authorization previously filed.</signatureName>
        <signatureDate>2005-08-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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