Deck joist span tables (2021 IRC)

Pressure-treated deck lumber — this is its span chart

A deck gets framed in pressure-treated 2× lumber, and people go looking for a "pressure treated span chart" as though it were a separate document. It is not: 2021 IRC Table R507.6 is the table, and the spans on this page are the ones a treated 2×6, 2×8, 2×10 or 2×12 deck joist is read at. The treatment is not a separate row — the row you read is set by the species group stamped on the piece, the spacing, and the load case for your address.

What the table does carry for treated lumber is the wet service factor: the reduction that applies to framing used where it stays wet, built into every cell here and into none of the floor joist cells. The species split follows the same outdoor reality — 2021 IRC Table R507.6 gives Southern pine, which is what most treated 2× stock east of the Rockies is cut from, its own line, and groups Douglas fir-larch / Hem-fir / Spruce-pine-fir on a second. Pressure-treated lumber in those three is normally incised, knife-slit so the preservative can penetrate, which lowers their published design values. The third line, Redwood / Western cedars / Ponderosa pine / Red pine, is the table's own grouping for those species and is read the same way.

One thing the span table has nothing to say about: which treatment retention level or which fasteners and connectors your deck needs. That is not in 2021 IRC Table R507.6, and this site does not guess at it — ask your building department or your lumber yard. 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.

What this table builds in

2021 IRC Table R507.6 is a deck table, not a floor table read outdoors. Its spans carry a 10 psf dead load, No. 2 grade, the wet service factor, and deflection held to L/360 — and it runs ground snow load cases a floor table never sees. That is why deck framing is read here rather than from the floor joist tables.

The load cases are 40 psf live load, 50 psf ground snow load, 60 psf ground snow load, 70 psf ground snow load. Ground snow load is the load on the ground at your address, published by your building department — not the depth of snow sitting on the deck. 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.

The common case, size by size

16-inch centers under the 40 psf live load case, across the 3 species groups 2021 IRC Table R507.6 lists. Each size links to its own page, where the same table is sliced to that size along with its cantilever row.

2021 IRC Table R507.6 — 40 psf live load, 10 psf dead load, No. 2 grade, wet service factor included, deflection L/360, at 16-inch centers. table source

Deck joist spans — the full table

Every size 2021 IRC Table R507.6 covers. Spacing runs across the top; load case and species group run down the side; the blocks are the lumber sizes.

2021 IRC Table R507.6 — 40 psf live load, 50 psf ground snow load, 60 psf ground snow load, 70 psf ground snow load; 10 psf dead load, No. 2 grade, wet service factor included, deflection L/360. table source

Deck joist cantilever limits — the full table

The cantilever columns are keyed to the joist back span — the span behind the support the joist runs past. Find the back span across the top, read down to the size, load case, and species group, and the cell is the longest cantilever 2021 IRC Table R507.6 lists for that combination. NP means not permitted by the table. Two conditions come with these columns as the table states them: a 220-pound point load at the free end of the cantilever, and deflection at the cantilever held to L/180 rather than the L/360 that applies to the back span.

2021 IRC Table R507.6 — maximum cantilever under the same load cases (40 psf live load, 50 psf ground snow load, 60 psf ground snow load, 70 psf ground snow load), with a 220-pound point load at the free end and deflection at the cantilever held to L/180. table source

The ledger that holds it to the house — 2021 IRC R507.9

Every span on this page ends somewhere, and at the house end it ends on a ledger bolted to the band joist. 2021 IRC Table R507.9.1.3(1) is read by the deck joist span — the same number the tables above give you — so the two belong on one page: pick the joist span, then read the fastener spacing that span requires.

R507.9.1.1 — the ledger. A deck ledger is at least a 2×8 nominal, in pressure-preservative-treated Southern pine, incised pressure-preservative-treated hem-fir, or approved naturally durable lumber, No. 2 grade or better. It does not carry point loads from beams or girders, and it is not fastened to stone or masonry veneer.

R507.9.1.2 — the band joist. The band joist behind the ledger is at least 2-inch nominal solid-sawn spruce-pine-fir or better, or a 1-inch nominal engineered wood rim board under R502.1.7, and it bears fully on the structure below.

R507.9.1.3 — the connection. The fasteners in this connection are hot-dipped galvanized or stainless steel, spaced by Table R507.9.1.3(1) and placed by Table R507.9.1.3(2).

Fastener spacing by joist span — 2021 IRC Table R507.9.1.3(1)

Load case down the left in blocks, deck joist span in feet down each block, and the three fastener-and-sheathing cases the table publishes across the top. Every figure is an on-centre spacing in inches. Sheathing here means whatever sits between the back of the ledger and the face of the band joist.

2021 IRC Table R507.9.1.3(1) — deck ledger connection to band joist, on-centre fastener spacing in inches. Fasteners are hot-dipped galvanized or stainless steel. table source

Where the fasteners go — 2021 IRC Table R507.9.1.3(2)

Spacing along the ledger is only half the connection; the other half is how close to an edge or an end a fastener may sit. These are minimum distances, and they are not the same on the ledger as on the band joist behind it.

2021 IRC Table R507.9.1.3(2) — minimum end and edge distances and spacing between rows. table source

What both tables' footnotes add

• A joist span between two rows may be interpolated. Reading past the ends of the table is not permitted.
• The ledger is flashed per R703.4 so water cannot reach the house band joist.
• These rows carry a 10 psf dead load, and snow load is not taken to act at the same time as live load.
• A lag screw's tip has to pass right through the inside face of the band joist.
• For the two ½-inch sheathing cases, that sheathing is wood structural panel or solid sawn lumber.
• For the 1-inch sheathing case, the sheathing may be wood structural panel, gypsum board, fiberboard, lumber or foam sheathing, and up to ½ inch of stacked washers may stand in for up to ½ inch of that thickness where it is combined with wood structural panel or lumber sheathing.
• Fasteners are staggered top to bottom along the run of the ledger.
• The end and row-spacing distances are minimums with a 5-inch maximum on them.
• For an engineered rim joist, the manufacturer's own instructions govern instead.

Two things this page will not do. It does not reproduce the two figures the code cites for staggering and for the bottom row's distance to the ledger's top edge — those state something only a drawing states, and a paraphrase of a drawing is a guess. And it says nothing about the lateral connection in R507.9.2, which is figure-dependent in the same way.

This is also one of the tables local amendment genuinely reaches: at least one state adopts the 2021 IRC with the load rows of this table narrowed rather than printed as they are here, without changing a single spacing figure in them. Read your own jurisdiction's adopted edition before you drill. 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

The rest of the deck

Deck joist sizes: 2×6 deck joists · 2×8 deck joists · 2×10 deck joists · 2×12 deck joists

The beam the joists land on is a different table: deck beam spans (2021 IRC Tables R507.5(1)–(4)). Indoors, the same sizes are read from the floor joist span tables.

Other assemblies: ceiling joist span tables · rafter span tables · header and girder spans

What all of it weighs on the way up the ladder — by size and by the same species groups this table is read by — is on the lumber weight page.