Deck joist span check
Maximum deck joist span for a lumber species, size and spacing, and whether your span works.
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Comes with the civil engineer plan: every tool for the role, from $10.20 a month at the launch price.
- Your own numbers, worked out as often as you like
- The full deck plan you can print or save to My work
- 4 cited sources, linked, with the checks to make
- Every other tool for the same role, in the same plan
- A plain-words read of your result (a fuller AI read with the Bifrost AI add-on)
Included in these role plans
Example result · fictional numbers
What you get: deck plan
Worked out by this tool from its default inputs. Its role plan lets you run your own numbers, print the sheet and save it.
13 2x8 joists at 16 in, 3 posts on 18 in footings, span works
- Maximum joist span
- 11 ft 9 15/16 in
- Your span
- 11 ft 0 in
- Result
- Works, with 0 ft 9 15/16 in to spare
- Max cantilever (rule of thumb)
- 2 ft 0 in
Framing plan
- Joists
- 13 × 2x8 at 16 in on center, 11 ft 0 in long (order 12 ft)
- Span check
- 11 ft 0 in of 11 ft 10 in allowed (IRC Table R507.6)
- Overhang
- None
- Ledger
- 2x8 (2x8 minimum), 1 × 16 ft; lags or through-bolts per DCA 6 Table 5 for the 11 ft 0 in joist span; flash over it; never into brick veneer
- Beam
- 1 beam, 16 ft 0 in long, posts every 8 ft 0 in; size it in IRC Table R507.5 for Southern pine, the 12 ft joist-span column and a 8 ft 0 in beam span
- Posts
- 3 × 6x6 (DCA 6 minimum), 3 per beam; check height in IRC R507.4
and 1 more lines
Also on the sheet
- Footings · 5 lines, starting with “Load on the busiest post”
- Hardware and order list · 6 lines, starting with “Joist hangers”
The plain-words read of this example
Southern pine 2x8 joists at 16 in can span 11 ft 10 in, so your 11 ft 0 in span works. A 16 ft deck takes 13 joists of 12 ft and 3 posts every 8 ft 0 in; the busiest post carries about 2,200 lb, so on 1,500 psf soil its footing needs about 18 in across. Size the beam from IRC Table R507.5, check the footing against DCA 6 Table 4, and use the larger. Flash and bolt the ledger to the house band and add the two 1,500 lb hold-downs; a loose ledger is how decks fail.
4 cited sources
- IRC 2021, Chapter 5 Floors (R507 Exterior decks) (International Code Council)
- DCA 6: Prescriptive Residential Wood Deck Construction Guide (2015 IRC) (American Wood Council, as posted by the Town of West Hartford, CT)
- IRC 2021, Chapter 4 Foundations (Table R401.4.1, R403.1.4) (International Code Council)
- Deck Center: deck code compliance (Simpson Strong-Tie)
Plus 7 step-by-step checks, a print layout and a link that reopens it with your numbers.