Do I Need a Permit to Build a Deck in Idaho?
Quick Answer
Yes — unless it's a small ground-level platform under 200 sq ft.
Idaho-specific rules
Adopted code: 2020 Idaho Residential Code (based on the 2018 IRC with Idaho amendments) — the statewide baseline under the Idaho Building Code Act, effective January 1, 2021. Local jurisdictions enforce it and may amend only to be more stringent.
When a Permit Is Required
Most jurisdictions require a deck permit for: decks over 200 square feet, decks more than 30 inches above grade, any deck attached to the house via a ledger board, and decks with structural modifications. A small freestanding platform under 200 sq ft and under 30 inches high may be exempt — but check with your city.
Footings and Frost Line
Deck footings must extend below the local frost line — the required depth varies by climate and elevation, so confirm the depth your city requires. This is one of the most common inspection points. Footings that are too shallow will fail inspection.
Guards and Railings
Guards are required when the deck surface is 30 inches or more above grade. Minimum guard height is 36 inches for residential decks (42 inches for commercial) under the IRC. Baluster spacing must be less than 4 inches — the classic 'sphere test' (a 4-inch sphere should not pass through).
Ledger Board Attachment
The ledger board (where the deck attaches to the house) is the #1 failure point for decks. Inspectors check that ledger boards are attached with lag screws or through-bolts — nails are never acceptable. Proper flashing above the ledger is also required to prevent water damage.
Bottom Line
Most useful decks need a permit. Plan for three inspections (footings, framing, final) and confirm your local frost-line footing depth.