Do I Need a Permit to Build a Deck in Montana?
Quick Answer
Yes — unless it's a small ground-level platform under 200 sq ft.
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.
Permit fees by city in Montana
Verified from each city’s published fee schedule. Where a city has no separate fee listed for this project, open the city page for the current requirements and amount.
| City | Permit fee | Source |
|---|---|---|
| Anaconda-Deer Lodge | $12.50Verifiedvia Residential Building Permit (New Construction) | Residential Building Permit (New Construction) → |
| Billings | $30.00Verifiedvia Residential Building Permit (New Construction) | Residential Building Permit (New Construction) → |
| Bozeman | (Administrative Charges/Employee/Hour + Inspector's Hourly Pay Rate) x Table A factor (amount of inspection time per sq ft, by construction type and fire rating) x Building Square FootageVerifiedvia Residential New Construction Permit | Residential New Construction Permit → |
| Butte-Silver Bow | $75.00 per hour, one-hour minimumVerifiedvia New Residential Construction Permit | New Residential Construction Permit → |
| Great Falls | Ranges from $62.61 (value $1-$1,000) up to $710.45 (value $49,001-$50,000), per the $1,000-increment table in Exhibit AVerifiedvia Residential Building Permit (New Construction) | Residential Building Permit (New Construction) → |
| Havre | $23.50Verifiedvia Residential Building Permit (New Construction / Addition / Remodel) | Residential Building Permit (New Construction / Addition / Remodel) → |
| Helena | Per Ordinance 3134 Appendix A valuation table, based on deck construction valuationVerified | Deck Permit → |
| Kalispell | $23.50Verifiedvia Residential Building Permit (New Construction) | Residential Building Permit (New Construction) → |
| Missoula | $36 permit fee + $11.00 plan review feeVerifiedvia Residential Building Permit (New Construction) | Residential Building Permit (New Construction) → |
| Unincorporated Yellowstone County | Calculated based on project valuation (fee schedule not published inline on the application; contact Building Codes Bureau at (406) 841-2056 for the current valuation-based fee table)Verifiedvia Residential Building Permit | Residential Building Permit → |