DeckSpec
IRC 2021 and 2024
Size the whole frame before you buy the lumber. Joist and beam spans, post and footing loads, ledger fastener spacing, guard and stair geometry — every result citing the IRC section it came from.
What it calculates
- Joist span and spacing for a given species, grade, and size
- Beam size and span given tributary width and post spacing
- Post size and footing area from the load path down to the soil
- Ledger fastener size, spacing, and required edge distances
- Guard height and infill spacing, plus stair rise, run, and stringer layout
- Cantilever and overhang limits
Code sections it cites
DeckSpec names the section behind every result so you can look it up, defend it to an inspector, or check it against the edition your town adopted. It describes what each section requires in plain language — it does not reproduce the code text itself. Why that matters.
IRC R507
The exterior deck provisions as a whole — the parent section every other deck reference below sits under.
IRC R507.3
Footing requirements: minimum sizes, bearing, and frost depth considerations.
IRC R507.4
Deck post requirements and how posts bear on their footings.
IRC R507.5
Deck beams, including the prescriptive beam span tables and bearing requirements.
IRC R507.6
Deck joists — allowable spans, spacing, and permitted cantilever limits.
IRC R507.7
Decking material and the span limits for decking boards.
IRC R507.9
Vertical and lateral attachment of the deck to the house, including ledger fastener schedules and the lateral load connection.
IRC R311.7
Stairway geometry: riser height, tread depth, headroom, and handrail requirements.
IRC R312.1
Guards — when one is required, how tall it must be, and opening limitations.
IRC Table R301.5
The minimum uniformly distributed live loads that decks are designed for.
Screenshots
Coming once the interface settles.
What it costs
Free
$0Ad-supported. No account required.
- Every calculator: joists, beams, posts and footings, ledger attachment, guards and stairs
- Section citation on every result
- Works fully offline
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DeckSpec Pro
$9.99- Export any calculation as a permit-ready PDF, with its code citations attached
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- One payment, on this device. No account, no subscription, nothing uploaded
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