Building permits in Lewis and Clark County, Montana
Find the right authority before you build. Lewis and Clark County permitting follows Montana law — here is exactly who issues the permit and where to start.
County + cities (mixed)
Lewis and Clark County Community Development & Planning (unincorporated areas); City of Helena issues within city limits
Lewis and Clark County issues building permits for unincorporated areas through its Community Development & Planning Department; the City of Helena issues permits within city limits.
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 Lewis and Clark County, Montana?
Lewis and Clark County Community Development & Planning (unincorporated areas); City of Helena issues within city limits is the permitting authority for Lewis and Clark County. Permitting is split — cities issue for incorporated areas, the county for unincorporated areas. Start at the official portal linked above.
Do I go to the county or my city for a building permit in Lewis and Clark County?
Permitting is split — cities issue for incorporated areas, the county for unincorporated areas.
What home projects need a permit in Lewis and Clark 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 Lewis and Clark County?
Use the official permit portal linked above. Most offices accept online submissions; have your plans, site information, and contractor details ready before applying.