Douglas fir-larch (DF-L) span tables (2021 IRC)

What the tables list for Douglas fir-larch

Cut in the West and the Rocky Mountain states — Douglas fir graded and sold together with western larch — and stocked through the western half of the country.

It carries the highest published values of the four at 2×8 No. 2: Fb = 1,240 psi and E = 1,600,000 psi (AWC Design Values for Joists and Rafters). Two numbers do the work in a span table — E is how much the piece sags under load, Fb is how hard it is to break in bending — and this species leads the four on both.

Across the 416 cells the six floor, ceiling and rafter tables list for all four species, Douglas fir-larch lists the longest span of the four outright in 344, ties for longest in 43, and lists the shortest in none of them. Against Southern pine alone, over the same 416 cells: Southern pine lists a longer span in 29, the same span in 42, and a shorter span in 345.

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.

Douglas fir-larch floor joist spans

Both floor joist tables the code publishes, sliced to Douglas fir-larch: grade and on-center spacing down the side, lumber size across the top. Each size column links to the page carrying that size across all four species.

The two tables differ in one thing: the live load the floor is checked against. Both carry the same 10 psf dead load and the same L/360 deflection limit, so the lighter live load is what lets the sleeping-area table list a longer span for the same stick of lumber. Both in full, all four species: the 2021 IRC floor joist span tables.

Douglas fir-larch ceiling joist spans

Both ceiling joist tables, sliced to Douglas fir-larch. These are attic floors, not living-area floors: the load cases are lighter and deflection is held to L/240, which is why so many cells run past the end of the table.

Both in full, all four species: the 2021 IRC ceiling joist span tables.

Douglas fir-larch rafter spans

Two of the eight rafter span tables in the 2021 IRC R802.4.1 set, sliced to Douglas fir-larch — both of them ceiling-not-attached cases, at the L/180 deflection limit those tables state. The other six load variants in that set are not covered on this site.

Both in full, all four species, plus the raised-tie note: the 2021 IRC rafter span tables.

Douglas fir-larch deck joist spans

2021 IRC Table R507.6 does not split these three. Douglas fir-larch, hem-fir and spruce-pine-fir share one line, and the deck spans below are that line — the same numbers for all three of them. Southern pine sits on its own line above it and lists a longer span in 47 of the 48 cells the two lines share.

Deck joists are quoted from their own table, not the floor table: 2021 IRC Table R507.6 carries a 10 psf dead load, No. 2 grade, the wet service factor for lumber that gets wet, and deflection held to L/360 — and it runs ground snow load cases a floor table never sees. This is the table pressure-treated deck framing is read from.

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, Douglas fir-larch / Hem-fir / Spruce-pine-fir. table source

The same table's cantilever limits — the maximum overhang past the beam, against each joist back span — are on the 2021 IRC deck joist span tables. The beam those joists land on is a different table again: deck beam spans.

Douglas fir-larch grades, and what the stamp says

Species is only half the row. Every species is graded, and the grade is a visual sort — how many knots, how big, where they fall, how straight the grain runs. Tighter sort, longer listed span. Taking a 2×8 Douglas fir-larch at 16-inch centers straight down the grade column of 2021 IRC Table R502.3.1(2):

• Select Structural — 13’7” — the tightest sort, and the longest span the table lists for this species and size.
• No. 1 — 13’1” — a step down in knot size and grain slope.
• No. 2 — 12’9” — the everyday framing grade, and the grade the R507 deck tables are listed for.
• No. 3 — 9’9” — the loosest sort of the four, and the shortest listed span.

No. 1 and No. 2 are different rows for Douglas fir-larch: of the 104 cells the six tables list at both grades, 3 match and the rest do not.

The number that applies is the one stamped on the piece. A grade stamp names the grading agency, the species or species combination, the grade, and the moisture condition at surfacing — and that stamp, not the invoice or the bin label, is what an inspector reads.

Headers and girders are not split by species

2021 IRC Tables R602.7(1) and R602.7(2) list one set of spans for Douglas fir-larch, hem-fir, Southern pine and spruce-pine-fir together, so a Douglas fir-larch header is read off the same row as any of the other three, with the same jack-stud count at each end. Those tables — exterior bearing walls, and the interior bearing walls and floor girders of R602.7(2) — are on the header and girder spans page.

Common questions

The other three species

Same tables, one species at a time: Southern pine spans · Hem-fir spans · Spruce-pine-fir spans

All four side by side, and why the same 2×8 lists a different span in each row: the species comparison.