Deck joist span calculator
Maximum allowable deck joist spans per IRC Table R507.5. Pressure-treated or naturally durable lumber — 40 psf live load, 10 psf dead load.
ft
Check against maxSpan check
16'-7" max — OK
Maximum allowable span
16'-7"
Douglas Fir-Larch #1 · 2x10 @ 16" o.c.
Douglas Fir-Larch #1 — All spans (IRC R507.5)
| Size | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|
| 2x6 | 10'-10" | 9'-10" | 8'-1" |
| 2x8 | 14'-4" | 13'-0" | 10'-8" |
| 2x10 | 18'-3" | 16'-7" | 13'-7" |
| 2x12 | 22'-2" | 20'-2" | 16'-6" |
Deck Joist Spans per IRC R507.5
Deck joist spans are governed by IRC Section R507.5, which provides separate tables from interior floor joists. Deck joists must be pressure-treated or naturally durable species (redwood, cedar) since they're exposed to weather.
Deck joist spans are generally shorter than interior floor joist spans for the same lumber size due to the different loading conditions and environmental exposure.
Key Differences from Interior Joists
- Must use pressure-treated or naturally durable lumber
- Cantilevers limited to 1/4 of the allowable joist span
- Lateral bracing required at supports
- No 19.2" o.c. option — only 12", 16", and 24"
Span values reference IRC Table R507.5. Always verify with your local building code. Not a substitute for professional engineering judgment.