How Far Can a Deck Joist Span?

A Southern Pine 2×10 at 16" centres spans 14 ft, per AWC DCA 6. The species is worth a foot, and your building department has the final say.

Start with the caveat, because it matters

This is a lookup of a published prescriptive table — Table 2 of the American Wood Council's DCA 6, Prescriptive Residential Wood Deck Construction Guide. That document is free, and it's written to be used exactly this way.

A prescriptive table is a set of pre-approved answers for ordinary cases. It is not an engineer, and it doesn't know about your site, your soil, a hot tub, a roof over the deck, or your snow load.

Your building department has the final say, always. Decks need a permit and an inspection in most jurisdictions, and local amendments are common. If your inspector's table differs from this one, theirs is the one that counts.

Your details

Species group

Check the grade stamp on the lumber. It changes the answer by up to a foot.

Joist size

Joist spacing

Span you need(ft)

FACE OF SUPPORT to face of support. Does NOT include the overhang.

Deck width(ft)

The direction the joists are spaced along — used for the joist count.

Result

Maximum allowable span

Feet, from DCA 6 Table 2. Your local code governs.

Span to spareFeet. NEGATIVE means the span you want is NOT allowed — deliberately signed.: 2
Maximum overhangFeet. The LESSER of the table figure and a quarter of your span.: 3
Overhang from the tableFeet. Not always larger at closer spacing — that is real, not a misprint.: 3.42
Quarter-span limitFeet. On ordinary spans this usually binds before the table figure does.: 3
Joists neededAcross the deck width, plus the one at the far end. Rim joists are extra.: 13
Joist lumberLinear feet, before overhangs, rim joists and waste.: 156
Deck depth achievableFeet, span plus the allowable overhang — how far the deck can come off the house on this framing.: 15

Open the Deck Joist Span Calculator on its own page to bookmark or share it.

The headline numbers

A Southern Pine 2×10 at 16" on centre spans 14 ft 0 in.

The same joist in other species:

Species group	2×10 @ 16" o.c.
Southern Pine	14' 0"
Douglas Fir-Larch / Hem-Fir / SPF	13' 7"
Redwood / Western Cedar / Ponderosa / Red Pine	13' 0"

A foot of span, from the sticker on the lumber. Two boards that look identical on the rack are not interchangeable here — check the grade stamp.

Measure the span the way the table means it

Face of support to face of support. It does not include the overhang.

This gets misread in both directions:

People measure the whole deck including the cantilever and conclude they're over the limit when they aren't
Or they measure to the centreline of the beam and conclude they're under it when they aren't

The overhang is a separate figure with its own separate limit.

Spacing is the cheapest lever you have

Take that Southern Pine 2×10:

24" on centre: 11' 5"
16" on centre: 14' 0"

Two and a half extra feet of span, for the cost of a few more joists.

Compare that with going up a nominal size, which means buying deeper lumber for the entire deck — and often deeper beams and a different ledger detail as well.

Try the spacing before you try the size.

The overhang quirk that looks like a misprint

Southern Pine 2×10 allowable overhang:

12" o.c. → 3' 1"
16" o.c. → 3' 5"
24" o.c. → 2' 10"

The overhang is larger at wider spacing, in the middle. That is not a typo — the AWC has a published FAQ addressing this exact question.

The reason: the overhang is governed by more than one criterion — deflection under distributed load, and a 220 lb point load applied at the tip. Which criterion binds changes with spacing, so the result isn't monotonic.

Read the figure off the table rather than reasoning about what it ought to be. This is a good general lesson about code tables: they're the output of several checks, and the binding one changes.

The overhang has a second limit too

It can never exceed one quarter of the actual span, whichever is smaller.

On a 12 ft span that's 3 ft — which, on most rows, binds before the table figure does. In the default case the table allows 3' 5" but the quarter-span rule caps you at 3' 0".

The calculator applies both and reports the smaller, which is what the guide requires.

What the table assumes

All of it matters, and if any of it isn't true for your deck, the numbers don't apply:

40 psf live load + 10 psf dead load — the ordinary residential figure
No. 2 grade lumber — a lower grade isn't covered at all
Wet service conditions
L/360 deflection limit
Incising assumed for Douglas Fir-Larch, Hem-Fir and SPF; the redwood/cedar group assumes northern species with no incising

A hot tub, a heavy planter wall, a roof over the deck, or significant snow means none of this applies and you need an engineer. Not a table, and not this page.

Two rules that override the span table entirely

A ledger must be at least a 2×8
So must any joist or rim joist that a guard post attaches to

Regardless of what the span table would otherwise allow for that size.

There's also a prescriptive ceiling of 18 ft on joist length in DCA 6, for footing design reasons — which is why the 2×12 entries stop there rather than continuing.

And the thing that actually causes collapses

Not joists.

Deck failures overwhelmingly happen at the ledger — the connection to the house — rather than in the middle of a span.

Flashing that keeps water out of the rim joist, and fastening into real structure rather than just sheathing, matter more than any number in this table.

Get the permit. Book the inspection before anything is covered up.