Most decks require a building permit. Here’s what triggers the permit requirement, what inspectors look for, and the IRC 2021 requirements for footings, ledgers, joists, guardrails, and stairs.
A building permit is required for most attached decks and for freestanding decks more than 30 inches above grade. The permit process involves a footing inspection, framing inspection, and final inspection. Key IRC 2021 requirements: footings below frost line, ledger properly flashed and bolted, joists within span limits, guardrails 36″ high with 4″ baluster spacing.
The general rule under IRC 2021 and most local codes:
The 30-inch threshold is where guardrail requirements kick in under IRC R312, which is also a common permit trigger. But local jurisdictions vary — some require permits for any deck regardless of height. Always call your building department before starting.
⚠️ Don’t skip the permit. An unpermitted deck can create disclosure issues at resale, void insurance claims if someone is injured, and result in a demolition order if discovered by the building department. The permit fee is minor compared to the risk.
Check your joist size, species, and spacing against IRC 2021 Table R507.5.
Deck footings must extend below the local frost depth. Frost depth varies from a few inches in Florida to 48″+ in Minnesota. Your building department will specify the required footing depth for your location. Footings must also bear on undisturbed soil or engineered fill.
The ledger board is the single most critical structural connection on an attached deck — and the most commonly failed inspection item. IRC R507.9 requires:
IRC Table R507.5 sets maximum allowable joist spans based on lumber species group, joist size, and on-center spacing. A 2×8 Southern Pine joist at 16″ o.c. can span up to 13′1″. Exceeding the allowable span requires either larger lumber, closer spacing, or an additional beam. Use the deck joist span calculator to check your specific situation.
Required on any deck surface more than 30″ above grade:
| Requirement | IRC 2021 Minimum |
|---|---|
| Guardrail height | 36″ (some interpretations 42″ above 30″) |
| Baluster spacing | 4″ sphere cannot pass through |
| Top rail load | 200 lb concentrated horizontal load |
| Bottom rail opening | 4″ sphere at base of rail |
| Post spacing | Typically 6′ max (verify structurally) |
Deck stairs follow the same IRC stair requirements as interior stairs. Maximum 8&frac3⁄4;″ rise, minimum 9″ run (10″ recommended for exterior), minimum 36″ width. A graspable handrail is required on stairs with four or more risers.
All wood used in ground contact or within 6″ of grade must be rated for ground contact (UC4A or UC4B). Joists and ledgers not in direct ground contact but in wet or exposed conditions require above-ground pressure treatment (UC3B). Connectors and fasteners must be hot-dipped galvanized or stainless steel rated for use with pressure-treated lumber — standard zinc-plated hardware corrodes rapidly in contact with PT wood.
Most building departments require the following documents with a deck permit application:
Species, size, spacing — instant pass/fail against IRC 2021 Table R507.5.
Do I need a permit to build a deck?
In most jurisdictions yes — attached decks almost always require a permit. Freestanding decks over 30 inches above grade typically require one. Always check with your local building department first.
What inspections are required for a deck?
Typically three: footing inspection before concrete is poured, framing inspection before decking is installed, and final inspection after all work is complete.
What is the minimum footing depth for a deck?
Below the local frost line, per IRC R403.1.4. Depth varies by location — ask your building department for the required depth in your area.
What are the guardrail requirements for a deck?
Required when deck surface is more than 30 inches above grade. Minimum 36 inches high. Balusters spaced so a 4-inch sphere cannot pass through. Top rail must withstand 200 lb concentrated load.
How is a deck ledger attached to the house?
With lag screws or through-bolts sized and spaced per IRC Table R507.9.1.3, with flashing installed between the ledger and house sheathing. Ledger attachment is the most commonly failed inspection item on decks.
Can I build a deck without a permit?
You shouldn't. Unpermitted decks create problems at resale, can void insurance, and may result in a demolition order. The permit fee is minimal compared to the risk.
Deck Joist Span Guide — Handrail & Guardrail Requirements — Stair Code Requirements — IRC 2021 Overview