Deck joist span chart
Pick the wood, the joist size and the spacing. You get the maximum span and overhang from the American Wood Council's deck guide, and whether your deck's span works, with every alternative that does.
Inputs
Result
| Joist | 12 in | 16 in | 24 in |
|---|
Deck joist span chart
Maximum span (LJ) and overhang (LO) from DCA 6 Table 2, for every species group, size and spacing.
| Species | Joist | Span at 12 in | 16 in | 24 in | Overhang at 12 in | 16 in | 24 in |
|---|
Values are from the American Wood Council's Prescriptive Residential Wood Deck Construction Guide (DCA 6-15, based on the 2015 IRC). They assume a 40 psf live load and 10 psf dead load, No. 2 grade lumber and wet service. Hot tubs, snow loads above 40 psf, roofs on the deck or a local code amendment all change the answer.
Reading the span
Joist span is measured from the face of the ledger, or the beam the joists hang from, to the face of the beam they rest on. It is not the joist's length and it does not include the overhang. The overhang is the part that cantilevers past the beam.
DCA 6 limits the overhang to the smaller of two numbers: the table value, and a quarter of the joist's actual span. A 2x10 Southern Pine joist at 16 in may overhang up to 3 ft 5 in by the table, but if its span is only 10 ft, the most it can overhang is 2 ft 6 in.
What the table assumes
- 40 psf live load and 10 psf dead load, the IRC load for decks.
- No. 2 grade lumber, wet service, deflection limited to span/360.
- Incised Douglas Fir-Larch, Hem-Fir and Spruce-Pine-Fir; Ponderosa and Red Pine from northern-species values with no incising.
- Joist length is limited to 18 ft in the guide for the footing design, so no span above 18 ft is listed.
Questions
How far can a 2x8 deck joist span?
At 16 in on centre, 11 ft 10 in in Southern Pine, 11 ft 1 in in Douglas Fir-Larch, Hem-Fir or SPF, and 10 ft 7 in in Redwood or Western Cedar, by DCA 6 Table 2. At 12 in on centre, 13 ft 1 in in Southern Pine.
How far can a 2x10 deck joist span?
At 16 in on centre, 14 ft in Southern Pine, 13 ft 7 in in Douglas Fir-Larch, Hem-Fir or SPF, and 13 ft in Redwood or Western Cedar. At 24 in on centre, 11 ft 5 in in Southern Pine.
How far can a 2x12 deck joist span?
At 16 in on centre, 16 ft 6 in in Southern Pine and 15 ft 9 in in Douglas Fir-Larch, Hem-Fir or SPF. At 12 in on centre, 18 ft, the most DCA 6 allows.
How far can a 2x6 deck joist span?
At 16 in on centre, 9 ft in Southern Pine, 8 ft 4 in in Douglas Fir-Larch, Hem-Fir or SPF, and 8 ft in Redwood or Western Cedar. 2x6 cannot be used as a ledger or for a joist carrying a guard post.
How far can deck joists cantilever?
Up to the overhang in DCA 6 Table 2, but never more than a quarter of the joist's actual span. A 2x10 Southern Pine joist at 16 in may overhang 3 ft 5 in if it spans at least 13 ft 8 in.
What spacing do I need for composite decking?
Usually 16 in on centre for straight boards and 12 in for diagonal boards, but it is set by the decking maker, not the joist table. Check the decking's installation guide.
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