Deck Joist Span Chart — IRC R507.6 Maximum Spans by Species & Spacing
Maximum deck joist spans from 2021 IRC Table R507.6: southern pine, DF-L/hem-fir/SPF, and redwood/cedar 2x6–2x12 joists at 12, 16, and 24 in o.c.
Updated August 20, 2026
How far a deck joist can span is a table lookup, not a judgment call: 2021 IRC Table R507.6 — published in identical form as Table 2 of the American Wood Council’s Prescriptive Residential Wood Deck Construction Guide (DCA 6) — fixes the maximum allowable span for every combination of species group, joist size, and on-center spacing. The table’s basis is a 40 psf live load plus 10 psf dead load, an L/360 deflection limit, No. 2 grade lumber, and wet service conditions, with incising assumed for the Douglas fir-larch / hem-fir / SPF group; the redwood / western cedars / ponderosa pine / red pine values are for northern species with no incising. One prescriptive cap rides the table: a 2×12 at 12″ o.c. is limited to 18′-0″ for footing design regardless of species.
The three tables below are generated from the same encoded R507.6 table the deck joist span calculator reads, so chart and tool can never drift apart. Beside each span is the maximum cantilever — the farthest the joists may overhang a dropped beam — computed as one-fourth of the joist span per the IRC R507.6 quarter-span rule. Southern pine spans the farthest of the three groups at every size, and tightening the spacing buys real reach: a southern pine 2×8 gains 15 inches of span going from 16″ to 12″ on center.
Southern pine — Maximum Joist Span (No. 2 grade)
| Joist size | Span @ 12″ o.c. | Cantilever @ 12″ (in) | Span @ 16″ o.c. | Cantilever @ 16″ (in) | Span @ 24″ o.c. | Cantilever @ 24″ (in) |
|---|---|---|---|---|---|---|
| 2x6 | 9 ft 11 in | 29.8 | 9 ft 0 in | 27.0 | 7 ft 7 in | 22.8 |
| 2x8 | 13 ft 1 in | 39.3 | 11 ft 10 in | 35.5 | 9 ft 8 in | 29.0 |
| 2x10 | 16 ft 2 in | 48.5 | 14 ft 0 in | 42.0 | 11 ft 5 in | 34.3 |
| 2x12 | 18 ft 0 in | 54.0 | 16 ft 6 in | 49.5 | 13 ft 6 in | 40.5 |
Spans per 2021 IRC Table R507.6 / AWC DCA 6 Table 2: 40 psf live + 10 psf dead, L/360 deflection, No. 2 grade, wet service. Cantilever = span ÷ 4 (IRC R507.6 quarter-span rule), computed — DCA 6’s own overhang column adds a 220 lb point-load deflection check and can allow less.
Douglas fir-larch / hem-fir / SPF — Maximum Joist Span (No. 2 grade)
| Joist size | Span @ 12″ o.c. | Cantilever @ 12″ (in) | Span @ 16″ o.c. | Cantilever @ 16″ (in) | Span @ 24″ o.c. | Cantilever @ 24″ (in) |
|---|---|---|---|---|---|---|
| 2x6 | 9 ft 6 in | 28.5 | 8 ft 4 in | 25.0 | 6 ft 10 in | 20.5 |
| 2x8 | 12 ft 6 in | 37.5 | 11 ft 1 in | 33.3 | 9 ft 1 in | 27.3 |
| 2x10 | 15 ft 8 in | 47.0 | 13 ft 7 in | 40.8 | 11 ft 1 in | 33.3 |
| 2x12 | 18 ft 0 in | 54.0 | 15 ft 9 in | 47.3 | 12 ft 10 in | 38.5 |
Spans per 2021 IRC Table R507.6 / AWC DCA 6 Table 2: 40 psf live + 10 psf dead, L/360 deflection, No. 2 grade, wet service. Cantilever = span ÷ 4 (IRC R507.6 quarter-span rule), computed — DCA 6’s own overhang column adds a 220 lb point-load deflection check and can allow less.
Redwood / western cedars / ponderosa pine / red pine — Maximum Joist Span (No. 2 grade)
| Joist size | Span @ 12″ o.c. | Cantilever @ 12″ (in) | Span @ 16″ o.c. | Cantilever @ 16″ (in) | Span @ 24″ o.c. | Cantilever @ 24″ (in) |
|---|---|---|---|---|---|---|
| 2x6 | 8 ft 10 in | 26.5 | 8 ft 0 in | 24.0 | 6 ft 10 in | 20.5 |
| 2x8 | 11 ft 8 in | 35.0 | 10 ft 7 in | 31.8 | 8 ft 8 in | 26.0 |
| 2x10 | 14 ft 11 in | 44.8 | 13 ft 0 in | 39.0 | 10 ft 7 in | 31.8 |
| 2x12 | 17 ft 5 in | 52.3 | 15 ft 1 in | 45.3 | 12 ft 4 in | 37.0 |
Spans per 2021 IRC Table R507.6 / AWC DCA 6 Table 2: 40 psf live + 10 psf dead, L/360 deflection, No. 2 grade, wet service. Cantilever = span ÷ 4 (IRC R507.6 quarter-span rule), computed — DCA 6’s own overhang column adds a 220 lb point-load deflection check and can allow less.
Sources & Further Reading
- 2021 International Residential Code, Table R507.6 — Deck Joist Spans for Common Lumber Species (40 psf live load), as encoded and verified in the deck joist span calculator
- AWC DCA 6-2015, Prescriptive Residential Wood Deck Construction Guide, Table 2 — Maximum Joist Spans and Overhangs (independent published reproduction; every span cell re-verified against it)
- Cantilever column: computed as span × 1/4 per IRC R507.6 (never transcribed)
Frequently Asked Questions
How far can a 2x8 deck joist span at 16 inches on center?
Per 2021 IRC Table R507.6 at 40 psf live load: 11 ft 10 in for southern pine, 11 ft 1 in for the Douglas fir-larch / hem-fir / SPF group, and 10 ft 7 in for redwood / western cedars. Tighten to 12″ o.c. and southern pine reaches 13 ft 1 in; open up to 24″ o.c. and it drops to 9 ft 8 in.
How far can deck joists cantilever past the beam?
One-fourth of the actual joist span, per IRC R507.6. A southern pine 2×10 spanning 14 ft 0 in (168 in) at 16″ o.c. may overhang up to 42 in. DCA 6’s Table 2 additionally checks a 220 lb point load at the overhang tip, which can trim the allowance for small joists — its printed overhang column governs where it is smaller.
What loads does Table R507.6 assume — and when does it not apply?
A 40 psf live load, 10 psf dead load, L/360 deflection, No. 2 grade lumber, and wet service, with incising assumed for Douglas fir-larch, hem-fir, and SPF. It does not cover decks where ground snow exceeds 40 psf or concentrated loads like hot tubs — those need engineered design.
Why do southern pine joists span farther than Douglas fir or cedar?
The table groups species by design values under wet-service deck conditions. Southern pine No. 2 carries the highest tabulated spans of the three groups at every size and spacing; the Douglas fir-larch / hem-fir / SPF group is tabulated with incising assumed (treatment incisions reduce design values), and the redwood / western cedars / ponderosa / red pine group has the lowest spans — about a foot less than southern pine at the common 2×8 @ 16″ setup.
Try the Calculators
Deck Joist Span Chart — IRC R507.6 Maximum Spans by Species & Spacing — reuven.tools/reference/deck-joist-spans — verified against: 2021 International Residential Code, Table R507.6 — Deck Joist Spans for Common Lumber Species (40 psf live load), as encoded and verified in the deck joist span calculator; AWC DCA 6-2015, Prescriptive Residential Wood Deck Construction Guide, Table 2 — Maximum Joist Spans and Overhangs (independent published reproduction; every span cell re-verified against it); Cantilever column: computed as span × 1/4 per IRC R507.6 (never transcribed)