Free Deck Building Code Calculator
Size your joists, beams, posts, footings and stairs to the IRC R507 deck codein seconds. Real span tables, your state's frost depth, and a permit-ready framing plan — no guessing, no fees.
Member sizes read from the IRC R507.6 (joists) and R507.5 (beams) tables for No. 2 Southern Pineat 40 psf live + 10 psf dead. Footings from tributary load ÷ soil bearing (R507.3); ledger fasteners per R507.9. Confirm with your local building department.
| Decking — Pressure-treated pine192 sq ft · ~28 × 16′ boards | $575–$1,730 |
| Substructure (joists, beam, posts, hardware)192 sq ft framing | $1,150–$2,495 |
| Footings (concrete piers)4 posts | $140–$360 |
| Railing / guard40 lin ft | $600–$2,400 |
| Stairs4 treads | $120–$380 |
| Permit + fasteners + miscallowance | $75–$500 |
| Total estimate | $2,660–$7,865 |
Low = DIY material budget; high = contractor-installed (labor included). Regional prices vary — treat as a planning range, not a quote.
Why build to the deck code?
Deck collapses are almost always a framing or connection failure — an undersized beam, joists spanning too far, a ledger lag-bolted into nothing, or footings that heaved out of the ground over one winter. That's why the building code (the IRC, Section R507) sets prescriptive span tables for exactly this: residential wood decks built without an engineer.
The trouble is the tables are dense — joist spans change with size, spacing and species; beam spans depend on the joist span they carry; footing depth tracks the frost line where you live. This calculator reads those tables for you and returns a complete framing plan: joist and beam sizes, post spacing, footing diameter and depth, stair layout and guard height — each with its code reference so your drawings match what the inspector checks.
Frequently asked questions
- How do I size deck joists, beams and footings?
- Pick the joist span from IRC Table R507.6 (by joist size, spacing and lumber species), the beam from Table R507.5 (by the joist span it carries), and the footing from the post's tributary load divided by your soil's bearing value. The calculator above does all three at once and shows the code reference for each.
- How far can a 2x8 deck joist span?
- A No. 2 Southern Pine 2x8 spans up to 13'1" at 12" on-center, 11'10" at 16", and 9'8" at 24" — per IRC R507.6. Douglas Fir-Larch and Hem-Fir span a little less, and cedar/redwood less again. The tool picks the smallest joist that clears your projection automatically.
- How deep do deck footings need to be?
- Footings must bear below the local frost line so they can't heave. That ranges from about 12" in frost-free states to 60" in the upper Midwest and New England. Choose your state in the calculator and it sets the depth; always confirm the exact figure with your building department.
- Do I need a permit to build a deck?
- Almost everywhere, yes — most jurisdictions require a permit for any deck attached to the house or more than ~30" above grade, and an inspection of the footings before they're poured. The calculator's framing plan is built to the IRC so your drawings line up with what the inspector checks.