How To – Joist Beam Dimension Chart for Deck Building

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    The following chart provides the distances and sizes of lumber necessary to build the beams that support your deck.

    The size on the left column describes the size of the beam necessary.

    For instance the left column may say 2-2×10″ which means you need to use Two – 2 inch x 10 inch boards that are nailed together to build the beam that supports your joists.

    When in doubt use a larger size beam meaning go up from a 8″ wide board to a 10″ if the dimensions recommended are close to the maximum.

     

     

     

    DECK BEAM SPANS
    Joists Spans (ft) Less Than or Equal to
    Southern Pine
    Size 6 8 10 12 14 16 18
    2-2×6 7′ – 1″ 6′ – 2″ 5′ – 6″ 5′ – 0″ 4′-8″ 4′ – 4″ 4′ – 1″
    2-2×8 9′ – 2″ 7′ – 11″ 7′ – 1″ 6′ – 6″ 6′ – 0″ 5′ – 7″ 5′ – 3″
    2-2×10 11′ – 10″ 10′ – 3″ 9′ – 2″ 8′ – 5″ 7′ – 9″ 7′ – 3″ 6′ – 10″
    2-2×12 13′ – 11″ 12′ – 0″ 10′ – 9″ 9′ – 10″ 9′ – 1″ 8′ – 6″ 8′ – 0″
    3-2×6 5′ – 7″ 7′ – 6″ 6′ – 11″ 6′ – 3″ 5′ – 10″ 5′ – 5″ 5′ 2″
    3-2×8 11′ – 4″ 9′ – 11″ 8′ – 11″ 8′ – 1″ 7′ – 6″ 7′ – 0″ 6′ – 7″
    3-2×10 14′ – 5″ 12′ – 10″ 11′ – 6″ 10′ – 6″ 9′ – 9″ 9 ‘ 1″ 8′ – 7″
    3-2×12 17′ – 5″ 15′ – 1″ 13′ – 6″ 12′ – 4″ 11′ – 5″ 10′ – 8″ 10′ – 1″
    Douglass Fir
    Larch
    Hem-Fir SPF2
    Redwood
    Western Cedars
    Size 6 8 10 12 14 16 18
    3×6 or 2-2×6 5′ – 6″ 4′ – 11″ 4′ – 4″ 4′ – 0″ 3′ – 8″ 3′ -5″ 3′ – 0″
    3×8 or 2-2×8 7′ – 2″ 6′ – 2″ 5′ – 6″ 5′ – 0″ 4′ – 8″ 4′ – 4″ 4′ – 0″
    3×10 or 2-2×10 8′ – 9″ 7′ – 7″ 6′ – 9″ 6′ 2″ 5′ – 8″ 5′ – 4″ 5′ – 0″
    3×12 or 2-2×12 10′ – 1″ 8′ – 9″ 7′ – 10″ 7′ – 2″ 6′ – 7″ 6′ – 2″ 5′ – 10″
    4×6 6′ – 6″ 5′ – 9″ 5′ – 2″ 4′ – 9″ 4′ – 4″ 4′ – 1″ 3′ – 10″
    4×8 8′ – 9″ 7′ – 7″ 6′ – 10″ 6′ – 3″ 5′ – 9″ 5′ – 5″ 5′ – 1″
    4×10 10′ – 9″ 9′ – 4″ 8′ – 4″ 7′ – 7″ 7′ – 1″ 6′ – 7″ 6′ – 3″
    4×12 12′ – 6″ 10′ – 10″ 9′ – 8″ 8′ – 10″ 8′ – 2″ 7′ – 8″ 7′ – 3″
    3-2×6 7′ – 4″ 6′ – 8″ 6′ – 2″ 5′ – 9″ 5′ – 4″ 5′ – 0″ 5′ – 1″
    3-2×8 9′ – 6″ 8′ – 9″ 7′ – 11″ 7′ – 3″ 6′ – 9″ 6′ – 3′ 5′ – 11″
    3-2×10 12′ – 4″ 10′ – 10″ 9′ – 6″ 8′ – 10″ 8′ – 2″ 7′ – 6″ 7′ – 4″
    3-2×12 14′ – 6″ 12′ – 7″ 11′ – 3″ 10′ – 3″ 9′ – 6″ 8′ – 11″ 8′ – 5″
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