IRC Deck Span Tables (2021)
Maximum deck joist spans (IRC R507.6) and built-up beam spans (IRC R507.5), in feet-inches. A 2×8 joist at 16″ on center spans 11'-10" in Southern Pine; a double 2×10 beam spans 10'-4" where the joists span 6 ft onto it. All values assume 40 psf live + 10 psf dead load.
Joist span — IRC R507.6
Clear span between supports, face of ledger to centre of beam. Species matters more than most people expect — the same 2×10 loses over a foot of span moving from Southern Pine to Spruce-Pine-Fir.
| Species | 2×6 | 2×8 | 2×10 | 2×12 | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| on center → | 12″ | 16″ | 24″ | 12″ | 16″ | 24″ | 12″ | 16″ | 24″ | 12″ | 16″ | 24″ |
| Southern Pine (SP)Most common pressure-treated stock in the East/South | 9'-11" | 9'-0" | 7'-7" | 13'-1" | 11'-10" | 9'-8" | 16'-2" | 14'-0" | 11'-5" | 18'-0" | 16'-6" | 13'-6" |
| Douglas Fir-Larch · Hem-Fir · Spruce-Pine-FirOne shared row in the code — identical spans for all three | 9'-6" | 8'-4" | 6'-10" | 12'-6" | 11'-1" | 9'-1" | 15'-8" | 13'-7" | 11'-1" | 18'-0" | 15'-9" | 12'-10" |
| Redwood · Western Cedars · Ponderosa Pine · Red PineNaturally durable species — the shortest spans in the table | 8'-10" | 8'-0" | 6'-10" | 11'-8" | 10'-7" | 8'-8" | 14'-11" | 13'-0" | 10'-7" | 17'-5" | 15'-1" | 12'-4" |
Cantilever past the beam is additional. IRC Table R507.6 caps it by back span — and prints NP where no cantilever is allowed at all, which catches most 2×6 decks. Check a cantilever.
Built-up beam span — IRC R507.5
Post-to-post span by deck joist span — the full distance the joists cover onto this beam, not half of it. Reading this table at the tributary width is the single most common way to over-span a beam. Values are Southern Pine #2; the other species groups are in the full R507.5(1) chart.
| Beam | 6 ft | 8 ft | 10 ft | 12 ft | 14 ft | 16 ft | 18 ft |
|---|---|---|---|---|---|---|---|
| (2) 2×6 | 6'-11" | 5'-11" | 5'-4" | 4'-10" | 4'-6" | 4'-3" | 4'-0" |
| (2) 2×8 | 8'-9" | 7'-7" | 6'-9" | 6'-2" | 5'-9" | 5'-4" | 5'-0" |
| (2) 2×10 | 10'-4" | 9'-0" | 8'-0" | 7'-4" | 6'-9" | 6'-4" | 6'-0" |
| (2) 2×12 | 12'-2" | 10'-7" | 9'-5" | 8'-7" | 8'-0" | 7'-5" | 7'-0" |
| (3) 2×6 | 8'-6" | 7'-5" | 6'-8" | 6'-1" | 5'-8" | 5'-3" | 4'-11" |
| (3) 2×8 | 10'-11" | 9'-6" | 8'-6" | 7'-9" | 7'-2" | 6'-8" | 6'-4" |
| (3) 2×10 | 13'-0" | 11'-2" | 10'-0" | 9'-2" | 8'-6" | 7'-11" | 7'-6" |
| (3) 2×12 | 15'-3" | 13'-3" | 11'-10" | 10'-9" | 10'-0" | 9'-4" | 8'-10" |
Column headings are the deck joist span in feet. Between two columns, interpolate — or let the beam span calculator do it and check your posts at the same time.
When these tables do not apply
- Snow load. Tabulated values are 40 psf live + 10 psf dead. Ground-snow regions may require a derate or an engineered design.
- Concentrated loads. A hot tub, a planter wall, an outdoor kitchen or a roof over the deck is outside prescriptive scope — these need engineering.
- Grade and treatment. Values assume #2 grade or better and ground-contact-rated lumber where required. A stamp you cannot read is a stamp you cannot rely on.
- Local amendments win. Many jurisdictions amend the IRC. Your building department's table is the one that gets inspected.
Source: 2021 International Residential Code §R507.5–R507.6 and AWC DCA-6, the prescriptive deck guide the IRC references. See our methodology and sources. This page is a reference, not a substitute for a permit review or a licensed designer.
Check your own numbers
Span table questions
What is the maximum span for a 2x8 deck joist?
At 16 inches on center, a 2×8 deck joist spans 11'-10" in Southern Pine and 11'-1" in Douglas Fir-Larch, Hem-Fir or Spruce-Pine-Fir — the IRC gives those three species a single shared row, so they are not three different spans. Tighten to 12 inches on center and Southern Pine reaches 13'-1". These are IRC 2021 Table R507.6 values for 40 psf live plus 10 psf dead load.
How far can a double 2x10 deck beam span?
A 2-ply 2×10 built-up beam in Southern Pine spans 10'-4" post-to-post where the joists span 6 ft onto it, 8'-0" at a 10 ft joist span, and 7'-4" at 12 ft. IRC Table R507.5(1) is indexed by the DECK JOIST SPAN — the full distance the joists cover — not by the tributary width, which is half of it. Reading the table at the tributary width is the most common way a deck beam ends up over-spanned.
Do beam span tables use tributary width or joist span?
Joist span. IRC Table R507.5(1) heads its columns "EFFECTIVE DECK JOIST SPAN LENGTH", so on a 12 ft deck you read the 12 ft column, not the 6 ft one. Tributary width — half the joist span each side — is what you use to work out the LOAD on the beam in pounds per foot; it is not the table index. Mixing the two reads a column for a deck half the size and allows a beam span the code does not.
Do these span tables include snow load?
The tables on this page are the 40 psf live load blocks. The IRC does publish heavier ones: Tables R507.5(2), (3) and (4) for beams and the 50, 60 and 70 psf blocks of R507.6 for joists, all indexed by GROUND SNOW load rather than by deck live load. A hot tub, planter wall or roof over the deck is a concentrated load that no prescriptive table covers — that needs an engineer.
Are joist spans measured to the centre of the beam?
Span is the clear distance between supports — face of ledger to centre of beam for a typical attached deck. A cantilever past the beam is additional, and IRC Table R507.6 tabulates how much is allowed by joist back-span. It prints NP — not permitted at all — for shallow joists past a certain back-span, and it permits well over 24 inches on deep ones: a Southern Pine 2×12 on an 18 ft back-span is allowed 4'-1".