Maximum span by grade
| Grade | Maximum span |
|---|---|
| Select Structural | 9′-6″ |
| No. 1 | 9′-1″ |
| No. 2 | 8′-11″ |
| No. 3 | 6′-10″ |
Span tables · Ceiling joists · 20 psf
20 psf live · L/240
2x4 Douglas Fir-Larch ceiling joist span at 16″ o.c.
At 16″ o.c., a 2x4 Douglas Fir-Larch #2 ceiling joist spans up to 8′-11″ under this table's load case. Select Structural and No. 1 reach further; No. 3 less. See the full grade breakdown below.
Douglas Fir-Larch #2, 20 psf
What this span means
This is the maximum clear span the Table R802.5.1(2) permits for a 2x4 Douglas Fir-Larch ceiling joist spaced 16″ o.c., carrying 20 psf of live load plus 10 psf dead load with a L/240 deflection limit. A blank cell means the span exceeds the maximum shown in the source table for that size.
Actual allowable spans depend on your real loads, the lumber's moisture and exact grade stamp, bearing and connection details, and any point loads or openings. Treat this as a starting point, then confirm the member with your local code and a design professional.
Source: International Residential Code (IRC), 2018 — Table R802.5.1(2) — Ceiling Joist Spans, 20 psf Live Load (limited attic storage). Published by International Code Council.
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