Deck beam spans (2021 IRC)

10 psf dead No. 2 grade wet service L/360 main span single span of joists

A Southern pine two-ply 2×10 deck beam spans up to 7’4” at an effective joist span of 12 feet, per 2021 IRC Table R507.5(1). All four beam tables are below, each with its own citation and a link to the table source.

40 psf live · 10 dead · wet service
7’4”
Per 2021 IRC Table R507.5(1) — Southern pine, two 2×10s fastened together, effective joist span 12 ft.

How the beam sizes are written

The size column pairs a ply count with a lumber size. “1-2×10” means a single 2×10; “3-2×12” means three 2×12s fastened together. On this page the same rows are printed as “2 × 2×10”, read as two 2×10s.

For a flush beam, the tables apply where the beam depth equals or exceeds the joist depth — that is a condition of the table, not a preference.

A deck beam is built from pressure-treated 2× lumber the same way the joists are, and these are the spans it is read at — there is no separate chart for treated stock. Treatment is not a row in these tables: the row is picked by the species group stamped on the piece, the ply count, and the effective joist span. The wet service factor for framing that stays wet is already carried in every cell, and the same three species-group lines the deck joist table uses run through these four. The deck joist span tables are the other half of the frame.

Effective joist span

The beam tables are not entered with the raw joist span. They are entered with the effective deck joist span: the actual deck joist span multiplied by the factor listed in 2021 IRC Table R507.5(5) for the ratio of joist cantilever to joist span. Where the joists do not cantilever past the beam, the factor listed is 0.66.

That entry only reads right on the beam these tables were written for. These tables cover a beam carrying a single span of joists, with or without joist cantilever. A beam with joists framing into it from both sides — the centre beam of a freestanding deck, say — carries about twice that floor area and is outside the tables: that's an engineer's question. Where the beam itself runs past its end post, that beam cantilever is limited to one-fourth of the adjacent beam span.

2021 IRC Table R507.5(5) — deck joist span factors
Cantilever ÷ joist span (C/J) Factor
0 (no cantilever) 0.66
1/12 0.72
1/10 0.80
1/8 0.84
1/6 0.90
1/4 1.00

2021 IRC Table R507.5(5) — factor applied to the deck joist span before entering the beam tables. table source

Deck beam span tables

Rows are species group and beam; columns are the effective joist span in feet. Values are quoted from the 2021 IRC exactly as the code prints them.

2021 IRC Table R507.5(1) — 40 psf live load

Beam Effective joist span (feet)
681012141618
Southern pine
1 × 2×6 4’7” 4’0” 3’7” 3’3” 3’0” 2’10” 2’8”
1 × 2×8 5’11” 5’1” 4’7” 4’2” 3’10” 3’7” 3’5”
1 × 2×10 7’0” 6’0” 5’5” 4’11” 4’7” 4’3” 4’0”
1 × 2×12 8’3” 7’1” 6’4” 5’10” 5’5” 5’0” 4’9”
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”
Douglas fir-larch / Hem-fir / Spruce-pine-fir
1 × 2×6 4’1” 3’6” 3’0” 2’8” 2’5” 2’3” 2’1”
1 × 2×8 5’6” 4’8” 4’0” 3’6” 3’2” 2’11” 2’9”
1 × 2×10 6’8” 5’10” 5’1” 4’6” 4’1” 3’9” 3’6”
1 × 2×12 7’9” 6’9” 6’0” 5’6” 5’0” 3’9” 3’6”
2 × 2×6 6’1” 5’3” 4’9” 4’4” 3’11” 3’7” 3’3”
2 × 2×8 8’2” 7’1” 6’4” 5’9” 5’2” 4’8” 4’4”
2 × 2×10 10’0” 8’7” 7’9” 7’0” 6’6” 6’0” 5’6”
2 × 2×12 11’7” 10’0” 8’11” 8’2” 7’7” 7’1” 6’8”
3 × 2×6 7’8” 6’8” 6’0” 5’6” 5’1” 4’9” 4’6”
3 × 2×8 10’3” 8’10” 7’11” 7’3” 6’8” 6’3” 5’11”
3 × 2×10 12’6” 10’10” 9’8” 8’10” 8’2” 7’8” 7’2”
3 × 2×12 14’6” 12’7” 11’3” 10’3” 9’6” 8’11” 8’5”
Redwood / Western cedars / Ponderosa pine / Red pine
1 × 2×6 4’2” 3’7” 3’1” 2’9” 2’6” 2’3” 2’2”
1 × 2×8 5’4” 4’7” 4’1” 3’7” 3’3” 3’0” 2’10”
1 × 2×10 6’6” 5’7” 5’0” 4’7” 4’2” 3’10” 3’7”
1 × 2×12 7’6” 6’6” 5’10” 5’4” 4’11” 4’7” 4’4”
2 × 2×6 6’2” 5’4” 4’10” 4’5” 4’0” 3’8” 3’4”
2 × 2×8 7’10” 6’10” 6’1” 5’7” 5’2” 4’10” 4’5”
2 × 2×10 9’7” 8’4” 7’5” 6’9” 6’3” 5’10” 5’6”
2 × 2×12 11’1” 9’8” 8’7” 7’10” 7’3” 6’10” 6’5”
3 × 2×6 7’8” 6’9” 6’0” 5’6” 5’1” 4’9” 4’6”
3 × 2×8 9’10” 8’6” 7’7” 6’11” 6’5” 6’0” 5’8”
3 × 2×10 12’0” 10’5” 9’4” 8’6” 7’10” 7’4” 6’11”
3 × 2×12 13’11” 12’1” 10’9” 9’10” 9’1” 8’6” 8’1”

2021 IRC Table R507.5(1) — 40 psf live load with 10 psf dead load, No. 2 grade, wet service, beam span measured between post centers, a single span of joists, beam cantilever limited to one-fourth of the adjacent beam span. table source

2021 IRC Table R507.5(2) — 50 psf ground snow load

Beam Effective joist span (feet)
681012141618
Southern pine
1 × 2×6 4’6” 3’11” 3’6” 3’2” 2’11” 2’9” 2’7”
1 × 2×8 5’9” 4’11” 4’5” 4’0” 3’9” 3’6” 3’3”
1 × 2×10 6’9” 5’10” 5’3” 4’9” 4’5” 4’2” 3’11”
1 × 2×12 8’0” 6’11” 6’2” 5’8” 5’3” 4’11” 4’7”
2 × 2×6 6’8” 5’9” 5’2” 4’9” 4’4” 4’1” 3’10”
2 × 2×8 8’6” 7’4” 6’7” 6’0” 5’7” 5’2” 4’11”
2 × 2×10 10’1” 8’9” 7’10” 7’1” 6’7” 6’2” 5’10”
2 × 2×12 11’11” 10’3” 9’2” 8’5” 7’9” 7’3” 6’10”
3 × 2×6 7’11” 7’2” 6’6” 5’11” 5’6” 5’1” 4’10”
3 × 2×8 10’5” 9’3” 8’3” 7’6” 6’11” 6’6” 6’2”
3 × 2×10 12’8” 10’11” 9’9” 8’11” 8’3” 7’9” 7’3”
3 × 2×12 14’11” 12’11” 11’6” 10’6” 9’9” 9’1” 8’7”
Douglas fir-larch / Hem-fir / Spruce-pine-fir
1 × 2×6 4’0” 3’5” 2’11” 2’7” 2’4” 2’2” 2’0”
1 × 2×8 5’4” 4’7” 3’11” 3’5” 3’1” 2’10” 2’8”
1 × 2×10 6’7” 5’8” 4’11” 4’5” 4’0” 3’8” 3’5”
1 × 2×12 7’7” 6’7” 5’11” 5’4” 4’10” 4’6” 4’2”
2 × 2×6 6’0” 5’2” 4’7” 4’2” 3’10” 3’5” 3’2”
2 × 2×8 8’0” 6’11” 6’2” 5’8” 5’0” 4’7” 4’2”
2 × 2×10 9’9” 8’5” 7’7” 6’11” 6’4” 5’10” 5’4”
2 × 2×12 11’4” 9’10” 8’9” 8’0” 7’5” 6’11” 6’6”
3 × 2×6 7’6” 6’6” 5’9” 5’3” 4’11” 4’7” 4’4”
3 × 2×8 10’0” 8’8” 7’9” 7’1” 6’6” 6’1” 5’8”
3 × 2×10 12’3” 10’7” 9’6” 8’8” 8’0” 7’6” 7’0”
3 × 2×12 14’3” 12’4” 11’0” 10’1” 9’4” 8’9” 8’3”
Redwood / Western cedars / Ponderosa pine / Red pine
1 × 2×6 4’1” 3’6” 3’0” 2’8” 2’5” 2’3” 2’1”
1 × 2×8 5’2” 4’6” 4’0” 3’6” 3’2” 2’11” 2’9”
1 × 2×10 6’4” 5’6” 4’11” 4’6” 4’1” 3’9” 3’6”
1 × 2×12 7’4” 6’4” 5’8” 5’2” 4’10” 4’6” 4’3”
2 × 2×6 6’1” 5’3” 4’8” 4’4” 3’11” 3’6” 3’3”
2 × 2×8 7’8” 6’8” 5’11” 5’5” 5’0” 4’8” 4’3”
2 × 2×10 9’5” 8’2” 7’3” 6’8” 6’2” 5’9” 5’5”
2 × 2×12 10’11” 9’5” 8’5” 7’8” 7’2” 6’8” 6’3”
3 × 2×6 7’1” 6’5” 5’11” 5’5” 5’0” 4’8” 4’5”
3 × 2×8 9’4” 8’4” 7’5” 6’10” — 5’11” 5’7”
3 × 2×10 11’9” 10’2” 9’1” 8’4” 7’8” 7’2” 6’9”
3 × 2×12 13’8” 11’10” 10’7” 9’8” 8’11” 8’4” 7’10”

2021 IRC Table R507.5(2) — 50 psf ground snow load with 10 psf dead load, No. 2 grade, wet service, beam span measured between post centers, a single span of joists, beam cantilever limited to one-fourth of the adjacent beam span. table source

The published 2021 IRC prints an unreadable value for this cell — confirm with your building department.

2021 IRC Table R507.5(3) — 60 psf ground snow load

Beam Effective joist span (feet)
681012141618
Southern pine
1 × 2×6 4’2” 3’7” 3’3” 2’11” 2’9” 2’6” 2’5”
1 × 2×8 5’3” 4’7” 4’1” 3’9” 3’5” 3’3” 3’0”
1 × 2×10 6’3” 5’5” 4’10” 4’5” 4’1” 3’10” 3’7”
1 × 2×12 7’5” 6’5” 5’9” 5’3” 4’10” 4’6” 4’3”
2 × 2×6 6’2” 5’4” 4’9” 4’4” 4’0” 3’9” 3’7”
2 × 2×8 7’10” 6’10” 6’1” 5’7” 5’2” 4’10” 4’6”
2 × 2×10 9’4” 8’1” 7’3” 6’7” 6’1” 5’8” 5’4”
2 × 2×12 11’0” 9’6” 8’6” 7’9” 7’2” 6’9” 6’4”
3 × 2×6 7’5” 6’9” 6’0” 5’6” 5’1” 4’9” 4’6”
3 × 2×8 9’9” 8’6” 7’8” 6’11” 6’5” 6’0” 5’8”
3 × 2×10 11’8” 10’2” 9’1” 8’3” 7’8” 7’2” 6’9”
3 × 2×12 13’9” 11’11” 10’8” 9’9” 9’0” 8’5” 7’11”
Douglas fir-larch / Hem-fir / Spruce-pine-fir
1 × 2×6 3’8” 3’1” 2’8” 2’4” 2’2” 2’0” 1’10”
1 × 2×8 5’0” 4’1” 3’6” 3’1” 2’10” 2’7” 2’5”
1 × 2×10 6’1” 5’2” 4’6” 4’0” 3’7” 3’4” 3’2”
1 × 2×12 7’1” 6’1” 5’5” 4’10” 4’5” 4’1” 3’10”
2 × 2×6 5’6” 4’9” 4’3” 3’10” 3’5” 3’1” 2’10”
2 × 2×8 7’5” 6’5” 5’9” 5’0” 4’6” 4’1” 3’9”
2 × 2×10 9’0” 7’10” 7’0” 6’4” 5’9” 5’2” 4’10”
2 × 2×12 10’6” 9’1” 8’1” 7’5” 6’10” 6’4” 5’10”
3 × 2×6 6’11” 6’0” 5’4” 4’11” 4’6” 4’2” 3’10”
3 × 2×8 9’3” 8’0” 7’2” 6’6” 6’1” 5’6” 5’0”
3 × 2×10 11’4” 9’10” 8’9” 8’0” 7’5” 6’11” 6’5”
3 × 2×12 13’2” 11’5” 10’2” 9’4” 8’7” 8’1” 7’7”
Redwood / Western cedars / Ponderosa pine / Red pine
1 × 2×6 3’9” 3’2” 2’9” 2’5” 2’2” 2’0” 1’11”
1 × 2×8 4’10” 4’2” 3’7” 3’2” 2’11” 2’8” 2’6”
1 × 2×10 5’10” 5’1” 4’6” 4’1” 3’8” 3’5” 3’3”
1 × 2×12 6’10” 5’11” 5’3” 4’10” 4’5” 4’2” 3’11”
2 × 2×6 5’7” 4’10” 4’4” 3’11” 3’6” 3’2” 2’11”
2 × 2×8 7’1” 6’2” 5’6” 5’0” 4’7” 4’2” 3’10”
2 × 2×10 8’8” 7’6” 6’9” 6’2” 5’8” 5’4” 4’11”
2 × 2×12 10’1” 8’9” 7’10” 7’2” 6’7” 6’2” 5’10”
3 × 2×6 6’8” 6’1” 5’5” 5’0” 4’7” 4’3” 3’11”
3 × 2×8 8’9” 7’9” — 6’4” — 5’5” 5’3”
3 × 2×10 10’11” 9’5” 8’5” 7’8” 7’3” 6’8” 6’3”
3 × 2×12 12’8” 10’11” 9’9” 8’11” 8’3” 7’9” 7’3”

2021 IRC Table R507.5(3) — 60 psf ground snow load with 10 psf dead load, No. 2 grade, wet service, beam span measured between post centers, a single span of joists, beam cantilever limited to one-fourth of the adjacent beam span. table source

The published 2021 IRC prints an unreadable value for this cell — confirm with your building department.

2021 IRC Table R507.5(4) — 70 psf ground snow load

Beam Effective joist span (feet)
681012141618
Southern pine
1 × 2×6 3’11” 3’4” 3’0” 2’9” 2’6” 2’4” 2’3”
1 × 2×8 4’11” 4’3” 3’10” 3’6” 3’3” 3’0” 2’10”
1 × 2×10 5’10” 5’1” 4’6” 4’2” 3’10” 3’7” 3’4”
1 × 2×12 6’11” 6’0” 5’4” 4’11” 4’6” 4’3” 4’0”
2 × 2×6 5’9” 5’0” 4’6” 4’1” 3’9” 3’6” 3’4”
2 × 2×8 7’4” 6’4” 5’8” 5’2” 4’10” 4’6” 4’3”
2 × 2×10 8’9” 7’7” 6’9” 6’2” 5’8” 5’4” 5’0”
2 × 2×12 10’3” 8’11” 8’0” 7’3” 6’9” 6’3” 5’11”
3 × 2×6 7’0” 6’3” 5’7” 5’1” 4’9” 4’5” 4’2”
3 × 2×8 9’3” 8’0” 7’2” 6’6” 6’0” 5’8” 5’4”
3 × 2×10 10’11” 9’6” 8’6” 7’9” 7’2” 6’8” 6’4”
3 × 2×12 12’11” 11’2” 10’0” 9’1” 8’5” 7’11” 7’5”
Douglas fir-larch / Hem-fir / Spruce-pine-fir
1 × 2×6 3’5” 2’10” 2’5” 2’2” 2’0” 1’10” 1’9”
1 × 2×8 4’7” 3’8” 3’2” 2’10” 2’7” 2’5” 2’4”
1 × 2×10 5’8” 4’9” 4’1” 3’8” 3’4” 3’1” 2’11”
1 × 2×12 6’7” 5’8” 5’0” 4’6” 4’1” 3’10” 3’7”
2 × 2×6 5’2” 4’6” 4’0” 3’5” 3’1” 2’10” 2’7”
2 × 2×8 6’11” 6’0” 5’3” 4’7” 4’1” 3’8” 3’5”
2 × 2×10 8’5” 7’4” 6’6” 5’10” 5’2” 4’9” 4’5”
2 × 2×12 9’10” 8’6” 7’7” 6’11” 6’4” 5’9” 5’4”
3 × 2×6 6’6” 5’7” 5’0” 4’7” 4’2” 3’9” 3’5”
3 × 2×8 8’8” 7’6” 6’8” 6’1” 5’6” 5’0” 4’7”
3 × 2×10 10’7” 9’2” 8’2” 7’6” 6’11” 6’4” 5’10”
3 × 2×12 12’4” 10’8” 9’7” 8’9” 8’1” 7’7” 7’1”
Redwood / Western cedars / Ponderosa pine / Red pine
1 × 2×6 3’6” 2’11” 2’6” 2’3” 2’0” 1’11” 1’9”
1 × 2×8 4’6” 3’10” 3’3” 2’11” 2’8” 2’6” 2’4”
1 × 2×10 5’6” 4’9” 4’2” 3’9” 3’5” 3’2” 3’0”
1 × 2×12 6’4” 5’6” 4’11” 4’6” 4’2” 3’11” 3’8”
2 × 2×6 5’3” 4’7” 4’1” 3’6” 3’2” 2’11” 2’8”
2 × 2×8 6’8” 5’9” 5’2” 4’8” 4’2” 3’10” 3’6”
2 × 2×10 8’2” 7’1” 6’4” 5’9” 5’4” 4’10” 4’6”
2 × 2×12 9’5” 8’2” 7’4” 6’8” 6’2” 5’9” 5’5”
3 × 2×6 6’4” 5’8” 5’1” 4’8” 4’3” 3’10” 3’6”
3 × 2×8 8’4” 7’3” 6’5” 5’11” 5’5” 5’1” 4’8”
3 × 2×10 10’2” 8’10” 7’11” 7’2” 6’8” 6’3” 5’11”
3 × 2×12 11’10” 10’3” 9’2” 8’4” 7’9” 7’3” 6’10”

2021 IRC Table R507.5(4) — 70 psf ground snow load with 10 psf dead load, No. 2 grade, wet service, beam span measured between post centers, a single span of joists, beam cantilever limited to one-fourth of the adjacent beam span. table source

Point loads, cantilevers beyond the table footnotes, unusual snow loads, or anything else outside the table's stated conditions — that's an engineer's question.

Common questions

What does 2-2x10 mean in the deck beam table?

It is the number of plies followed by the lumber size. A 1-2×10 beam is a single 2×10; a 2-2×10 is two 2×10s fastened together; a 3-2×12 is three 2×12s fastened together. Each ply count is its own row in the table, so read the row that matches the beam you have.

What is the effective joist span the deck beam table is entered with?

The beam tables are entered with the effective deck joist span, which is the actual joist span multiplied by the factor listed in 2021 IRC Table R507.5(5). That factor depends on the ratio of the joist cantilever to the joist span; where the joists do not cantilever past the beam, the factor listed is 0.66. The tables behind that entry cover a single span of joists, beam cantilever limited to one-fourth of the adjacent beam span.

Do the deck beam tables cover a beam with joists framing in from both sides?

No. These tables cover a beam carrying a single span of joists, with or without joist cantilever. A beam with joists framing into it from both sides — the centre beam of a freestanding deck, say — carries about twice that floor area and is outside the tables: that's an engineer's question. Where the beam itself runs past its end post, that beam cantilever is limited to one-fourth of the adjacent beam span.

How far apart should deck posts be?

No farther apart than the beam on top of them may span. Every cell in Tables R507.5(1) to (4) is a maximum beam span measured between post centers, so the post spacing along a beam is read from the beam's row: its species group, its ply count and size, and the effective joist span it carries. A two-ply 2×10 Southern pine beam at a 12-foot effective joist span, for instance, is listed at 7’4” under a 40 psf live load (Table R507.5(1)) — posts no more than that far apart, center to center. Where the beam itself runs past its end post, that beam cantilever is limited to one-fourth of the adjacent beam span. On a single-level deck the post itself is sized by a different table, R507.4 (deck post height), which this site does not carry.

Which of the four deck beam tables applies?

Table R507.5(1) covers a 40 psf live load; Tables R507.5(2), (3) and (4) cover 50, 60 and 70 psf ground snow loads. Use the table that matches the load case for your location, and confirm the ground snow load with your building department.

Deck joists

The joists the beam carries have their own table — 2021 IRC Table R507.6, in full on the deck joist span tables page, or by size: 2×6 deck joists , 2×8 deck joists , 2×10 deck joists , 2×12 deck joists .

Local codes amend these tables and your inspector has the final word — confirm with your building department.