Assumptions & Data Source
Transparency for builders, inspectors, and anyone verifying our deck joist span tool.
Official source
All span and overhang figures come from American Wood Council DCA 6-15, Table 2. Maximum Joist Spans and Overhangs, in the Prescriptive Residential Wood Deck Construction Guide based on the 2015 IRC.
PDF: awc.org — AWC-DCA62015-DeckGuide-1804.pdf
Design assumptions (from Table 2 footnotes)
- 40 psf live load and 10 psf dead load
- No. 2 grade lumber
- Wet service conditions
- Main span deflection limit L/360
- Overhang: cantilever length/180 deflection with 220 lb point load; also ≤ L/4 of actual span
- Incising assumed for Douglas Fir-Larch, Hem-Fir, and Spruce-Pine-Fir
- Ponderosa Pine and Red Pine use northern-species values without incising
- Ledger minimum 2x8; joists/rim joists with guard posts minimum 2x8
- Joist length limited to 18'-0" for the guide’s footing design
What we did (and did not do)
We transcribed Table 2 cells into data/span-table.json as literal feet-inch strings and documented the copy in data/TABLE2-TRANSCRIPTION.md. We did not invent spans, average competitor sites, or adjust for snow, hot tubs, or roofs.
Limits of this site
Single-level residential decks within DCA 6 scope only. Not a substitute for the IRC, local amendments, or a licensed engineer. See the footer disclaimer on every page.