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 |
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| 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″ |