-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 BEyyhaXYtY1UtxwZRp09atfP7UVAIgS++hBgw7Y3dyXd3SMauxyt+KLPNOpIg5Mj
 nIDh2zRgklENSoR42ZL6iA==

<SEC-DOCUMENT>0001241931-03-000001.txt : 20030812
<SEC-HEADER>0001241931-03-000001.hdr.sgml : 20030812
<ACCEPTANCE-DATETIME>20030812141324
ACCESSION NUMBER:		0001241931-03-000001
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20030811
FILED AS OF DATE:		20030812

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			NADEAU BERTIN F
		CENTRAL INDEX KEY:			0001241931

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-08584
		FILM NUMBER:		03837034

	MAIL ADDRESS:	
		STREET 1:		606 RUE CATHCART BUREAU 1035
		CITY:			MONTREAL
		STATE:			A8
		ZIP:			H3B 1K9

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
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>

<ownershipDocument>

    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2003-08-11</periodOfReport>


    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001241931</rptOwnerCik>
            <rptOwnerName>NADEAU BERTIN F</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>606 RUE CATHCART BUREAU 1035</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MONTREAL</rptOwnerCity>
            <rptOwnerState>A8</rptOwnerState>
            <rptOwnerZipCode>H3B 1K9</rptOwnerZipCode>
            <rptOwnerStateDescription>QUEBEC, CANADA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>

        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2003-08-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>32.18</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4000</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By solely owned company, Casavant Freres</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>

    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">1,097 additional shares are held indirectly by solely owned company, Financiere Nadeau Ltd.</footnote>
    </footnotes>


    <ownerSignature>
        <signatureName>William G. Miller, signed pursuant to authorization previously filed</signatureName>
        <signatureDate>2003-08-12</signatureDate>
    </ownerSignature>

</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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