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Guides / Decks and patios · Updated

Deck beam span chart

From IRC 2021 Table R507.5(1), 40 psf live load. Your town can amend it, so the building department has the final say.

Short answer

With 12 ft joists in southern pine, a double 2x10 beam spans 7 ft 4 in post to post. A double 2x12 spans 8 ft 7 in, and a triple 2x12 spans 10 ft 9 in. Longer joists mean shorter beam spans.

How to read it

Find the column for how far your joists span to the beam. Then go down to your beam. The number is the farthest apart your posts can be. A 2-2x10 is two 2x10s nailed together.

Joist span here is the effective span. If your joists hang past the beam, see the factor below first.

Max beam span

Southern pine: max beam span by joist span
Beam6 ft8 ft10 ft12 ft14 ft16 ft18 ft
1-2x64 ft 7 in4 ft3 ft 7 in3 ft 3 in3 ft2 ft 10 in2 ft 8 in
1-2x85 ft 11 in5 ft 1 in4 ft 7 in4 ft 2 in3 ft 10 in3 ft 7 in3 ft 5 in
1-2x107 ft6 ft5 ft 5 in4 ft 11 in4 ft 7 in4 ft 3 in4 ft
1-2x128 ft 3 in7 ft 1 in6 ft 4 in5 ft 10 in5 ft 5 in5 ft4 ft 9 in
2-2x66 ft 11 in5 ft 11 in5 ft 4 in4 ft 10 in4 ft 6 in4 ft 3 in4 ft
2-2x88 ft 9 in7 ft 7 in6 ft 9 in6 ft 2 in5 ft 9 in5 ft 4 in5 ft
2-2x1010 ft 4 in9 ft8 ft7 ft 4 in6 ft 9 in6 ft 4 in6 ft
2-2x1212 ft 2 in10 ft 7 in9 ft 5 in8 ft 7 in8 ft7 ft 5 in7 ft
3-2x68 ft 6 in7 ft 5 in6 ft 8 in6 ft 1 in5 ft 8 in5 ft 3 in4 ft 11 in
3-2x810 ft 11 in9 ft 6 in8 ft 6 in7 ft 9 in7 ft 2 in6 ft 8 in6 ft 4 in
3-2x1013 ft11 ft 2 in10 ft9 ft 2 in8 ft 6 in7 ft 11 in7 ft 6 in
3-2x1215 ft 3 in13 ft 3 in11 ft 10 in10 ft 9 in10 ft9 ft 4 in8 ft 10 in
Douglas fir-larch, hem-fir, SPF: max beam span by joist span
Beam6 ft8 ft10 ft12 ft14 ft16 ft18 ft
1-2x64 ft 1 in3 ft 6 in3 ft2 ft 8 in2 ft 5 in2 ft 3 in2 ft 1 in
1-2x85 ft 6 in4 ft 8 in4 ft3 ft 6 in3 ft 2 in2 ft 11 in2 ft 9 in
1-2x106 ft 8 in5 ft 10 in5 ft 1 in4 ft 6 in4 ft 1 in3 ft 9 in3 ft 6 in
1-2x127 ft 9 in6 ft 9 in6 ft5 ft 6 in5 ftSee codeSee code
2-2x66 ft 1 in5 ft 3 in4 ft 9 in4 ft 4 in3 ft 11 in3 ft 7 in3 ft 3 in
2-2x88 ft 2 in7 ft 1 in6 ft 4 in5 ft 9 in5 ft 2 in4 ft 8 in4 ft 4 in
2-2x1010 ft8 ft 7 in7 ft 9 in7 ft6 ft 6 in6 ft5 ft 6 in
2-2x1211 ft 7 in10 ft8 ft 11 in8 ft 2 in7 ft 7 in7 ft 1 in6 ft 8 in
3-2x67 ft 8 in6 ft 8 in6 ft5 ft 6 in5 ft 1 in4 ft 9 in4 ft 6 in
3-2x810 ft 3 in8 ft 10 in7 ft 11 in7 ft 3 in6 ft 8 in6 ft 3 in5 ft 11 in
3-2x1012 ft 6 in10 ft 10 in9 ft 8 in8 ft 10 in8 ft 2 in7 ft 8 in7 ft 2 in
3-2x1214 ft 6 in12 ft 7 in11 ft 3 in10 ft 3 in9 ft 6 in8 ft 11 in8 ft 5 in
Redwood, western cedar, ponderosa or red pine: max beam span by joist span
Beam6 ft8 ft10 ft12 ft14 ft16 ft18 ft
1-2x64 ft 2 in3 ft 7 in3 ft 1 in2 ft 9 in2 ft 6 in2 ft 3 in2 ft 2 in
1-2x85 ft 4 in4 ft 7 in4 ft 1 in3 ft 7 in3 ft 3 in3 ft2 ft 10 in
1-2x106 ft 6 in5 ft 7 in5 ft4 ft 7 in4 ft 2 in3 ft 10 in3 ft 7 in
1-2x127 ft 6 in6 ft 6 in5 ft 10 in5 ft 4 in4 ft 11 in4 ft 7 in4 ft 4 in
2-2x66 ft 2 in5 ft 4 in4 ft 10 in4 ft 5 in4 ft3 ft 8 in3 ft 4 in
2-2x87 ft 10 in6 ft 10 in6 ft 1 in5 ft 7 in5 ft 2 in4 ft 10 in4 ft 5 in
2-2x109 ft 7 in8 ft 4 in7 ft 5 in6 ft 9 in6 ft 3 in5 ft 10 in5 ft 6 in
2-2x1211 ft 1 in9 ft 8 in8 ft 7 in7 ft 10 in7 ft 3 in6 ft 10 in6 ft 5 in
3-2x67 ft 8 in6 ft 9 in6 ft5 ft 6 in5 ft 1 in4 ft 9 in4 ft 6 in
3-2x89 ft 10 in8 ft 6 in7 ft 7 in6 ft 11 in6 ft 5 in6 ft5 ft 8 in
3-2x1012 ft10 ft 5 in9 ft 4 in8 ft 6 in7 ft 10 in7 ft 4 in6 ft 11 in
3-2x1213 ft 11 in12 ft 1 in10 ft 9 in9 ft 10 in9 ft 1 in8 ft 6 in8 ft 1 in

No. 2 grade, wet service, 10 psf dead load. In-between joist spans can be interpolated. "See code" marks two cells we couldn't confirm from a clean copy.

When the joists overhang the beam

Multiply your joist span by this factor to get the effective joist span, then use that column.

Overhang ÷ joist spanFactor
No overhang0.66
1/120.72
1/100.80
1/80.84
1/60.90
1/41.00

12 ft joists with a 2 ft overhang is 1/6, so the effective span is 12 × 0.90 = 10.8 ft.

Building the beam

Nail the plies together with two rows of 10d nails, 16 in apart, on each side. The beam needs 1 1/2 in of bearing on a wood post or metal cap, 3 in on concrete. It can run past the last post a quarter of its span.

These spans assume 40 psf of people and furniture. A hot tub loads a deck far past that, so its beam needs an engineer.

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