Building permits in Yellowstone County, Montana
Find the right authority before you build. Yellowstone County permitting follows Montana law — here is exactly who issues the permit and where to start.
Cities issue permits
City of Billings Building Division (Yellowstone County does not issue building permits)
Yellowstone County does not issue building permits or certificates of occupancy for structures outside city limits; the City of Billings Building Division issues permits within Billings (and Laurel issues its own). Unincorporated areas fall under the Montana state building-code program administered by the MT DLI.
Permit cheat-sheet (Montana rules)
| Project | Permit? | Authority | Typical fee | Timeline | Go / No-Go | Key notes |
|---|---|---|---|---|---|---|
| 🏠 Accessory Dwelling Unit (ADU) | Conditional | city | Where a certified city/county enforces, fees follow that jurisdiction; in non-certified areas a single-family home is exempt from the state building permit (trade permits still apply). Verify locally. | Where enforced, plan review typically 1-4 weeks depending on scope. | Case by case | ADU allowances are set by local zoning. In certified cities (Billings, Missoula) a permit is required; in non-certified areas, residential buildings with fewer than five dwelling units are exempt from the state building permit under MCA 50-60-102, though state electrical/plumbing/mechanical permits are still required. |
| 🪵 Deck / Porch | Conditional | city | Where enforced, fees follow the local schedule; verify locally. | Where enforced, simple decks often over-the-counter to a few weeks. | Generally allowed | In certified cities a permit is required for elevated or attached decks. In non-certified areas, single-family homes are exempt from the state building permit. State trade permits still apply. Exempt: Freestanding decks not over 30 in above grade are typically exempt (2021 IRC R105.2). Billings requires a permit for decks over 30 in above grade. |
| 🧱 Fence / Wall | Conditional | city | Where enforced, fencing permits apply above local height limits; verify locally. | Where enforced, often over-the-counter. | Generally allowed | Local zoning sets height/setback rules. Confirm with your city building department. |
| 🛖 Shed / Outbuilding | Conditional | city | Where enforced, small detached sheds may be exempt; verify locally. | Where enforced, often over-the-counter. | Generally allowed | In non-certified areas a single-family home (and its accessory structures) is exempt from the state building permit, but state electrical/plumbing/mechanical permits still apply. Confirm locally. Exempt: Billings exempts detached sheds not exceeding 200 sq ft. In non-certified areas, single-family residential is exempt from the state building permit. |
| 🪜 Basement Finish | Conditional | city | Where a certified city enforces, a building permit fee applies; in non-certified areas the state building permit is exempt for single-family homes (trade permits still apply). Verify locally. | Where enforced, typically several weeks for full plan review. | Generally allowed | Finishing a basement into habitable space requires permits (egress, framing, electrical, plumbing, mechanical) where a code is enforced. In non-certified areas, the state building permit is exempt for single-family homes but trade permits are still required. |
| 🚗 Garage / Carport | Conditional | city | Where enforced, attached garages (additions) are permitted; verify locally. | Where enforced, typically several weeks for plan review. | Generally allowed | An attached garage is an addition requiring a permit where a code is enforced. A small detached garage may be exempt (e.g., Billings exempts detached sheds/accessory structures under 200 sq ft). In non-certified areas, single-family homes are exempt from the state building permit. |
| ☀️ Rooftop Solar PV | Permit required | state | Electrical permit required statewide by the MT DLI Building Codes Program (NEC); local jurisdictions may also be involved. | Electrical permits are typically issued promptly. | Generally allowed | Rooftop solar PV requires a state electrical permit (Montana requires electrical permits statewide regardless of local building-code adoption). Structural modifications may also need a permit where a local code is enforced. |
| 🌡️ HVAC Replacement | Permit required | state | Mechanical permit required statewide by the MT DLI Building Codes Program; licensed contractors perform the work. | Mechanical permits are typically issued promptly. | Generally allowed | Furnace/AC/heat-pump replacement requires a mechanical permit, which Montana requires statewide regardless of whether the local government enforces building codes. |
| 🍳 Kitchen Remodel | Conditional | city | Where enforced, a building permit plus trade permits apply; verify locally. | Where enforced, typically several weeks for full plan review. | Generally allowed | Relocating plumbing/electrical or moving walls requires a permit where a code is enforced. In non-certified areas, single-family homes are exempt from the state building permit but electrical/plumbing/mechanical permits are still required. Cosmetic-only work may be exempt. |
| 🛁 Bathroom Remodel | Conditional | city | Where enforced, a building permit plus trade permits apply; verify locally. | Where enforced, typically several weeks for full plan review. | Generally allowed | Relocating plumbing/electrical or moving walls requires a permit where a code is enforced. In non-certified areas, single-family homes are exempt from the state building permit but trade permits are still required. |
| 🏗️ Room Addition | Conditional | city | Where a certified city enforces, a building permit based on valuation applies; in non-certified areas the state building permit is exempt for single-family homes (trade permits still apply). Verify locally. | Where enforced, typically several weeks for full plan review. | Generally allowed | Room additions require a full building permit where a code is enforced. In non-certified areas, single-family residential is exempt from the state building permit under MCA 50-60-102, but state electrical/plumbing/mechanical permits still apply. |
| 🪟 Window / Door Replacement | Conditional | city | Where enforced, a permit fee applies if enlarging the opening; in-kind swap often exempt. Verify locally. | Where enforced, in-kind swaps often same-day. | Generally allowed | Enlarging or adding openings requires a permit where a code is enforced. Confirm locally. |
| 🏘️ Roof Replacement | Conditional | city | Where enforced, an in-kind re-roof may be exempt; structural deck replacement requires a permit. Verify locally. | Where enforced, simple re-roofs often over-the-counter. | Generally allowed | Billings notes re-siding/re-roofing often does not require a plan. Structural deck replacement triggers a full building permit. Confirm locally. |
| 🅿️ Driveway / Parking Pad | Conditional | city | No building permit for private flatwork where enforced; a right-of-way permit may be needed. Verify locally. | Where enforced, often over-the-counter. | Generally allowed | A permit may be required for right-of-way work. Confirm with your city building department. |
| 🏊 Swimming Pool / Spa | Conditional | city | Where enforced, a building permit plus barrier fencing applies; verify locally. | Where enforced, typically several weeks. | Generally allowed | Pools need a permit and barrier fencing where a code is enforced. Confirm with your local building department. |
| 🧱 Retaining Wall | Conditional | city | Where enforced, a permit applies if over 4 ft; verify locally. | Where enforced, often over-the-counter to a few weeks. | Generally allowed | Walls over 4 ft or supporting a surcharge require a permit. Confirm with your local building department. Exempt: Retaining walls not over 4 ft (bottom of footing to top) and not supporting a surcharge are exempt (2021 IRC R105.2). |
| 💥 Demolition / Teardown | Permit required | city | Demolition permit fee set by the issuing authority; verify locally. | — | Generally allowed | A full teardown or major strip-out requires a demolition (building) permit. Municipalities require utility disconnects (electric, gas, water, sewer) and, for pre-1978 homes, an asbestos/lead-paint clearance before demolition. |
| 🚰 Septic System | Permit required | county | Septic permit fee set by the local environmental/health authority; engineered systems cost more. | — | Generally allowed | New or replacement onsite wastewater (septic) systems require a permit from the Montana Department of Environmental Quality (subsurface wastewater treatment systems under ARM 17.36); site evaluation and engineered design are typically required and permits are issued locally by the county sanitarian. |
| 🔌 EV Charger | Conditional | city | Electrical permit; fee set by the issuing authority. | — | Generally allowed | A home EV charging station (240V branch circuit + wall-mounted EVSE) requires an electrical permit and must meet the NEC (Article 625). Many jurisdictions fast-track residential EVSE. |
| ⚡ Standby Generator | Conditional | city | Mechanical/electrical permit; fee set by the issuing authority. | — | Generally allowed | A permanently installed standby generator requires mechanical and electrical permits (transfer switch, fuel gas/propane line). Setback, carbon-monoxide ventilation, and noise rules apply. |
Frequently asked questions
Who issues building permits in Yellowstone County, Montana?
City of Billings Building Division (Yellowstone County does not issue building permits) is the permitting authority for Yellowstone County. Permits are issued by the incorporated cities; the county handles only unincorporated areas. Start at the official portal linked above.
Do I go to the county or my city for a building permit in Yellowstone County?
Permits are issued by the incorporated cities; the county handles only unincorporated areas.
What home projects need a permit in Yellowstone County?
The same project types shown in the cheat-sheet above (ADU, deck, fence, shed, solar, and more) — rules follow Montana state law. Whether the county or your city issues it depends on your property's incorporation status.
How do I apply for a permit in Yellowstone County?
Use the official permit portal linked above. Most offices accept online submissions; have your plans, site information, and contractor details ready before applying.