ADU Regulations in Montana (MT)
Montana is rated Easy for ADU construction with an ADU-friendliness score of 78/100 (Very ADU-Friendly). Montana has a statewide ADU law that sets baseline rules across all municipalities. No owner-occupancy requirement. No additional parking required for ADUs. Montana passed SB 245 and HB 429 in 2023, requiring cities with over 5,000 population to allow at least one ADU per single-family lot. The law prohibits owner-occupancy requirements and parking mandates for ADUs. Montana's reforms were driven by severe housing shortages in cities like Bozeman and Missoula.
Full ADU Regulations Summary for Montana
| ADUs Allowed | Yes |
| Statewide ADU Law | Yes |
| Maximum ADU Size | Set locally |
| Owner Occupancy Required | No |
| Parking Required | No |
| Minimum Setback | Set locally |
| Permitting Timeline | Varies by jurisdiction |
| Impact Fees | Limited by state law |
| Long-Term Rental Allowed | Yes |
| Short-Term Rental (Airbnb) Allowed | Yes |
| Ease of Building | Easy |
ADU Regulations by City in Montana
ADU rules can vary by city even within the same state. While Montana's statewide law sets minimum standards, some cities have additional local provisions. Below are ADU details for 3 cities in Montana.
Bozeman
ADUs allowed by right. Bozeman has high ADU demand due to housing costs. No owner-occupancy requirement per state law.
Missoula
ADUs permitted on most residential lots. Missoula was already ADU-friendly before the state mandate.
Helena
ADUs allowed per state law. Helena updated zoning in 2024 for compliance.
How Montana Compares to Other States
Below is a comparison of Montana with five states that have similar ADU-friendliness scores. This comparison helps illustrate where Montana stands nationally.
| State | Score | Statewide Law | Parking Req? | Owner Occ? | Ease |
|---|---|---|---|---|---|
| Montana (MT) | 78 | Yes | No | No | Easy |
| Florida (FL) | 78 | Yes | No | No | Easy |
| Nevada (NV) | 78 | Yes | No | No | Moderate |
| Maine (ME) | 80 | Yes | No | No | Easy |
| New York (NY) | 76 | Yes | No | Yes | Easy |
| Hawaii (HI) | 75 | Yes | No | No | Moderate |
Frequently Asked Questions About ADUs in Montana
Can I build an ADU in Montana?
Yes, ADUs are allowed in Montana. Montana has a statewide ADU law that requires local jurisdictions to permit ADUs on residential lots. This means your city cannot outright ban ADUs. The ease of building is rated "Easy" with a friendliness score of 78/100.
Do I need to live on the property to have an ADU in Montana?
No, Montana does not require owner occupancy for ADUs. You can rent out both the main house and the ADU, which maximizes rental income potential.
How big can an ADU be in Montana?
Montana does not set a statewide maximum ADU size — this is determined by your local jurisdiction. Common local limits range from 600 to 1,200 square feet. Check your city's zoning code for the specific maximum.
Do I need extra parking for an ADU in Montana?
No, Montana does not require additional parking for ADUs. This is a significant advantage, as parking requirements are often the biggest barrier to ADU construction on smaller lots.
Can I rent out my ADU in Montana?
Yes, long-term rentals of ADUs are allowed in Montana. Short-term rentals (like Airbnb) are also generally permitted, though your city may have separate short-term rental regulations.
How long does it take to get an ADU permit in Montana?
The permitting timeline in Montana is: Varies by jurisdiction. The statewide law sets maximum review periods that cities must comply with. Actual timelines can be affected by plan review backlogs, inspection scheduling, and the complexity of your project. Pre-approved ADU plans, where available, can significantly speed up the process.
Check ADU Rules for Your City
Use our ADU regulations lookup tool to find the specific rules for your city in Montana, or browse all 50 states to compare ADU regulations across the country. Remember that local rules may be more specific than state-level regulations.