How far can a 2x8 joist span for a deck?
| Most common case — 2x8, Southern Pine, 16″ o.c. | 11′ 10″ |
|---|---|
| Same size in redwood or cedar | 10′ 7″ |
| Maximum cantileverone quarter of the ACTUAL span, not of this maximum | 2′ 11″ |
| — Southern Pine — | |
| 2x8 at 12″ o.c. | 13′ 1″ |
| 2x8 at 16″ o.c.the spacing most decks are built at | 11′ 10″ |
| 2x8 at 24″ o.c. | 9′ 8″ |
| — Douglas Fir-Larch — | |
| 2x8 at 12″ o.c. | 12′ 6″ |
| 2x8 at 16″ o.c.the spacing most decks are built at | 11′ 1″ |
| 2x8 at 24″ o.c. | 9′ 1″ |
| — Redwood, Western Cedar — | |
| 2x8 at 12″ o.c. | 11′ 8″ |
| 2x8 at 16″ o.c.the spacing most decks are built at | 10′ 7″ |
| 2x8 at 24″ o.c. | 8′ 8″ |
| — Other sizes, Southern Pine at 16″ — | |
| 2x6 at 16″ o.c., Southern Pine | 9′ 0″ |
| 2x8 at 16″ o.c., Southern Pine | 11′ 10″ |
| 2x10 at 16″ o.c., Southern Pine | 14′ 0″ |
| 2x12 at 16″ o.c., Southern Pine | 16′ 6″ |
Notes
- Species is worth more than most people expect. The same 2x8 at 16″ o.c. spans 11′ 10″ in Southern Pine and 10′ 7″ in redwood or cedar — a difference of 1′ 3″ on the identical board. Buying whatever the yard has in stock can quietly cost you a post line.
- Spacing buys less than going up a size. Dropping from 24″ to 12″ o.c. takes this 2x8 from 9′ 8″ to 13′ 1″ — 3′ 5″ for twice the joists. Going up to a 2x10 at 16″ reaches 14′ 0″ instead.
- This is the JOIST table, not the beam table. Joists carry the decking; the beam carries the joists and is sized from a different table against the joist span. A 2x8 joist spanning 11′ 10″ needs a beam sized for that span, and the beam is almost always a built-up member of two or three plies.
- Four assumptions, and all four have to hold. 40 psf live plus 10 psf dead, No. 2 grade, wet service conditions, no cantilever included in the span. A hot tub, a planter wall, a roof over the deck, or a jurisdiction with snow load all put the deck outside this table.
- Cantilever is a quarter of the ACTUAL span. If your joists run 10 ft, the overhang can be 2½ ft — not a quarter of the 11′ 10″ maximum. This is read wrong constantly and it is the difference between a springy deck edge and a failing one.
- The building official has the last word. Local amendments to the IRC are common and are usually stricter. Pull the permit before buying lumber.
What the 2x8 table says
Every number above is IRC Table R507.6 for deck joists: 40 psf live load, 10 psf dead, No. 2 grade lumber, wet service conditions, no cantilever included.
The three spacings and three species groups are the whole table for this size. Read down the species you can actually buy locally, not the one with the longest span.
Joists and beams are different tables
This is the joist span — how far the boards carrying the decking can run between supports. The beam that carries those joists is sized from a separate table against the joist span, and it is almost always a built-up member of two or three plies rather than a single board.
Sizing a beam from the joist table is the most consequential mistake in deck framing, and it is common because both tables look alike.
Cantilever is a quarter of the actual span
Not a quarter of the maximum in the table. If your joists run 10 ft, the overhang can be 2½ ft, whatever the maximum for that size happens to be.
Nearby sizes
Read more
- How to Tell if a Deck Is Unsafe: The Seven Checks, in Order of What Kills PeopleDeck collapses are almost never a broken board. They are the ledger letting go, all at once, with everyone standing on it.
- Deck Post Size by Height: When 4×4 Stops Being AllowedThe 8 ft line is where 4×4 stops. Above it the question is not only size but bracing, and the connection at each end matters more than the post between them.
- Deck Beam Span Table: Why the Span Depends on the Joists, Not the DeckA beam span table has two inputs, and the one people forget is the joist span the beam is carrying. Read it with one input and the answer is wrong by feet.
- Deck Joist Cantilever: One Quarter of the Actual Span, Not the MaximumThis is the most misread line in the deck code, and it is misread in the direction that puts the beam too far in.