Montana is now one of the most ADU-friendly states in the country, thanks to recent legislation requiring cities, towns, and zoned counties to allow a minimum of one accessory dwelling unit (ADU) on any lot with an existing single-family home.
If you’re considering building an ADU for rental income, family housing, or long-term flexibility, there are several key regulations you should understand. Keep reading to learn more about ADU requirements in your part of Montana.
Are ADUs Allowed in Montana?
Yes. Under MCA 76-2-345 (for municipalities) and SB 532 (for counties with zoning), local governments must allow at least one ADU by right on any lot that contains a single-family dwelling.
This means the ADU must be approved without a special hearing, variance, or discretionary review as long as it meets the state’s requirements.
ADUs That Are Allowed in Montana
Most places in Montana allow ADUs up to 1,000 square feet or 75% of the primary home’s floor area, whichever is smaller, as required by state law. Some cities and counties may allow larger ADUs, but none may be more restrictive than these statewide standards. All of the ADUs shown below fall within Montana’s permitted size range and can be used where local zoning and building requirements allow ADUs.
The A-Frame ADU
The Grove ADU
The Luna ADU
The Rivara
The Sonoma ADU
What Is Considered An ADU in Montana?
According to the Montana Code annotated 2023, an ADU is a self-contained living space located on the same lot as a larger single-family home, featuring its own kitchen, bedroom, and bathroom facilities, and adhering to or being exempt from relevant building codes, fire codes, and public health and safety regulations as outlined in Title 50, chapter 2.
If you think a tiny home might be a better fit for your needs, read our article on Montana’s Tiny Home Regulations to find out what’s allowed in your area.
Can Park Model Tiny Homes Be Used as ADUs in Montana?
Not automatically. Montana’s ADU laws require units to comply with (or be exempt from) residential building, fire, and health codes. Park model RVs and movable tiny homes typically do not meet Montana’s residential building or energy code standards, as noted in Montana Department of Environmental Quality (DEQ)’s Energy Code Best Practices.Because of this, they generally cannot qualify as ADUs unless a city or county specifically allows them and verifies they meet all code requirements. Always check with your local jurisdiction for confirmation.
Curious as to what other states have to say about tiny home ADUs? Take a look at the table below.
| AL | IL | MN | NC | TX |
| AZ | IN | MS | ND | UT |
| AR | IA | MO | OH | VT |
| CA | KS | MT | OK | VA |
| CO | KY | NE | OR | WA |
| CT | LA | NV | PA | WV |
| DE | ME | NH | RI | WI |
| FL | MD | NJ | SC | WY |
| GA | MA | NM | SD | |
| ID | MI | NY | TN |
Can Log Cabins Be Used as an ADU in Montana?
Yes, if they meet all applicable codes. A prefab log cabin can function as ADUs as long as it:
- is located on the same parcel as a single-family dwelling
- remains smaller than the primary dwelling
- meets all applicable building, fire, sanitation, and energy code requirements
- complies with the statewide ADU size limits (less than or equal to 75% of the main home’s floor area or less than or equal to 1,000 sq. ft., whichever is less)
If these conditions are met, a log-style unit may be approved the same way as any other ADU.
Can Modern Cabins Be Used as an ADU in Montana?
Yes. A modern-style cabin can qualify as an ADU if it:
- is smaller than the primary dwelling
- meets all applicable codes
- fits within statewide size limits
- receives required local building/zoning approvals
Montana law also prohibits cities and counties from requiring matching exterior design or materials, so a modern cabin does not need to match the primary home. Zook Cabins has several contemporary cabin models that fit within these parameters. As with any ADU, the deciding factor is always local zoning compliance, so we highly recommend checking your municipality for specific guidelines in your area.
What is the Difference Between a Prefab ADU & a Modular ADU?
The difference between these structures lies mainly in how they are constructed and delivered.
- Prefab ADUs
Built entirely off-site and delivered fully assembled. Must still comply with Montana building, fire, and health codes when placed on a permanent foundation (unless exempt). - Modular ADUs
Constructed off-site in sections, then assembled on-site. Modular units are typically reviewed under the same building codes as site-built homes.
Regardless of construction method, an ADU in Montana must comply with code requirements applicable to dwelling units.
What is the Minimum Size for an Accessory Dwelling Unit?
Montana does not set a statewide minimum square footage for ADUs. However, an ADU must meet applicable building, fire, and public health standards, which establish functional minimums for habitable space (room size, sanitation, ventilation, etc.). We suggest checking with your town’s planning and zoning department to be certain of the latest rules before planning your ADU project.
Can My ADU be Bigger Than My House?
No. Montana law states that an attached or detached ADU cannot exceed:
- 75% of the gross floor area of the single-family dwelling, or
- 1,000 sq. ft., whichever is less
This limitation applies statewide for municipalities and zoned counties.
How Close To My House Can I Build An ADU?
Montana’s ADU statutes do not establish statewide setback numbers. Therefore, setback rules are determined by local jurisdictions, and we strongly suggest checking with your local building or planning office for specific setback measurements.
Do You Need A Permit For An ADU in Montana?
You sure do. Every ADU in Montana requires a building permit, which confirms compliance with zoning, safety, and construction standards. In addition to the building permit, you may also need electrical, plumbing, and HVAC permits, plus environmental health permits if you’re connecting to a septic system. This process might seem like an additional headache
Are There Any Incentives or Grants for ADUs in montana?
No, as of right now, Montana doesn’t have any state-wide programs for ADU grants or financial assistance. With more statewide legislation potentially coming through, it is possible that there may be more federal or state funding available. If affordability is a concern, it’s worth asking your municipality if any temporary initiatives or pilot programs are in place.
Are Zook Cabin’s ADUs Built to Code?
Definitely! All of Zook’s ADUs are designed to meet and exceed all local building codes for your area and are thoroughly inspected. No matter how you utilize your ADU, you can rest assured knowing all the codes and permits are taken care of.
Can an ADU Have Multiple Bedrooms and Bathrooms?
Yes. As long as your ADU is within size and code requirements, multi-bedroom layouts are permissible. Zook Cabins offers several 1 bedroom ADU models that are perfect for a cozier, minimalist lifestyle. We also design and sell several two bedroom models that may fit the needs of a small family better. Our Grove ADU has the option for two bedrooms and two bathrooms while still fitting under 1,000 square feet!
Are ADUs A Good Investment?
Yes. ADUs are a valuable investment, offering multiple financial benefits. They generate extra income through rental opportunities and, in certain areas, can be sold independently of the main house. Also, the addition of an ADU can enhance the property’s total market value, significantly improving its potential for resale.
As noted, some areas have restrictions on owner occupancy and the ability to sell an ADU separately, so read on to learn what your locality allows.
What Are the Requirements for ADUs in Each County in Montana?
Below is a list of all 56 counties in Montana, along with their ADU requirements and the appropriate government officials to contact for questions or to certify your ADU plans. All areas in Montana, regardless of local government rules, must allow at least one ADU that is 800 square feet, 16 feet in height, and no more than 4 feet from the rear and side property lines. However, each county may enforce slightly different minimum and maximum size standards beyond the state baseline.
You can skip this list to view the requirements for your city.
Does Anaconda-Deer Lodge County Allow ADUs?
Yes. Anaconda-Deer Lodge County allows ADUs in areas where zoning applies, and all ADUs must meet the statewide requirements under MCA 76-2-345 and SB 532.
Maximum Square Footage:
- Up to 75% of the primary dwelling’s floor area or 1,000 sq. ft., whichever is less.
- Larger sizes may be allowed only if the county’s zoning district permits it.
Setbacks:
- The county cannot impose stricter setbacks, height limits, or lot coverage standards on ADUs than those applied to the primary dwelling.
- Exact setback numbers vary by zoning district.
Please contact the Anaconda-Deer Lodge County Planning Department to confirm zoning coverage for your property and to verify applicable standards.
Does Beaverhead County Allow ADUs?
Yes, but Beaverhead County has very limited zoning. ADUs are allowed under state law, but only areas with adopted zoning districts are required to approve ADUs by right.
Maximum Square Footage:
- Up to 75% of the main home or 1,000 sq. ft., whichever is less.
Setbacks:
- Setbacks may not be stricter for ADUs than for the primary dwelling.
- In non-zoned areas, general building/septic placement rules apply instead of zoning setbacks.
Other Requirements:
- No additional parking or owner-occupancy rules may be imposed.
ADUs must comply with building, sanitation, and public health codes.
Please contact the Beaverhead Land Services Department to confirm that your parcel is inside a zoned area and what standards apply.
Does Big Horn County Allow ADUs?
Yes, Big Horn allows ADUs, but does not administer countywide zoning.
ADU approvals depend primarily on state building, sanitation, and subdivision regulations.
Maximum Square Footage:
- Less than or equal to 75% of the primary home or 1,000 sq. ft., whichever is less.
Setbacks:
- Since there is no countywide zoning, there are no zoning setbacks for ADUs.
- Building codes, well/septic separation distances, and floodplain rules still apply.
Please contact the Big Horn Planning and Zoning Office to confirm placement rules relevant to your parcel.
Does Blaine County Allow ADUs?
Yes, Blaine County allows ADUs, but does not have countywide zoning.
ADUs in this county default to state law and building/sanitation requirements, with no county zoning overlay.
Maximum Square Footage:
- Less than or equal to 75% of the main dwelling or 1,000 sq. ft. (state limit).
Setbacks:
- No zoning setbacks apply outside municipal boundaries.
- Only building code separation distances and sanitation rules apply.
Please contact the Blaine County Planning Office to verify requirements for your specific parcel.
Does Broadwater County Allow ADUs?
Yes. Broadwater County has limited zoning, and ADUs are allowed under state law wherever zoning exists.
Maximum Square Footage:
- Up to 75% of the primary dwelling’s area or 1,000 sq. ft., whichever is less.
Setbacks:
- Setbacks for ADUs cannot be stricter than those applied to the primary dwelling.
- In areas without zoning, only construction and sanitation codes govern placement.
Other Requirements:
- No parking, owner-occupancy, or design-matching requirements can be imposed.
- ADUs must comply with Montana building and sanitation regulations.
Please contact the Broadwater Community Development & Planning Department to determine if your location falls within a zoning district.
Does Butte-Silver Bow County Allow ADUs?
Yes. Butte-Silver Bow is a consolidated city-county with zoning, and ADUs must be allowed by right under MCA 76-2-345.
Maximum Square Footage:
- Less than or equal to 75% of the primary dwelling or 1,000 sq. ft.
- Larger sizes may be permitted depending on the zoning district.
Setbacks:
- ADUs cannot face stricter setbacks, height limits, or lot coverage restrictions than the main house.
- Actual setback distances vary by zoning district.
Please contact the Butte–Silver Bow City-County Planning Department to confirm zoning district standards for your property.
Does Carbon County Allow ADUs?
Yes, ADUs are allowed under Montana state law, but Carbon County does not administer countywide zoning. This means ADUs are regulated primarily through state building, sanitation, and subdivision requirements, not zoning.
Maximum Square Footage:
- Up to 75% of the main dwelling or 1,000 sq. ft., whichever is less.
Setbacks:
- No countywide zoning setbacks apply.
- Only building code separations, floodplain regulations, and sanitation distances apply.
Please contact the Carbon County Planning & Development to confirm parcel-specific constraints or local municipal requirements inside city limits.
Does Carter County Allow ADUs?
Yes. Carter County allows ADUs, but the county has no countywide zoning. ADUs therefore follow state ADU law and standard building/sanitation rules.
Maximum Square Footage:
- Less than or equal to 75% of the primary home or 1,000 sq. ft. (state limit).
Setbacks:
- No zoning setbacks apply outside municipalities.
- Only state building code and sanitation clearances apply.
Please contact the Carter County Commissioners Office to determine any local considerations such as floodplain or septic capacity.
Does Cascade County Allow ADUs?
Yes. Cascade County has zoning in certain areas, and ADUs must be allowed by right in those zones under MCA 76-2-345 and SB 532.
Maximum Square Footage:
- Up to 75% of the primary dwelling or 1,000 sq. ft., whichever is less.
Setbacks:
- Setbacks for ADUs cannot be stricter than setbacks for the primary dwelling.
- Actual setback distances depend on your specific zoning district.
Please contact the Cascade County Planning Division to verify if your parcel lies within a zoning district and which standards apply.
Does Chouteau County Allow ADUs?
Yes, Chouteau County allows ADUs, but has no countywide zoning, so ADU regulation is dictated by state law and building/sanitation requirements rather than zoning districts.
Maximum Square Footage:
- Less than or equal to 75% of the principal dwelling or 1,000 sq. ft.
Setbacks:
- No zoning setbacks apply.
- Setbacks instead come from building code separations and sanitation rules.
Please contact the Chouteau County Planning Department for parcel-specific placement guidance.
Does Custer County Allow ADUs?
Yes, Custer County allows ADUs, but the county does not administer countywide zoning. ADUs rely on Montana’s statewide rules plus building/sanitation requirements.
Maximum Square Footage:
- Less than or equal to 75% of the main home or 1,000 sq. ft.
Setbacks:
- No zoning setbacks apply outside incorporated municipalities.
- Building code separations, well/septic distances, and floodplain standards apply.
Please contact the Custer County Land Use Department for confirmation of local infrastructure and septic capacity requirements.
Does Daniels County Allow ADUs?
Yes. Daniels County allows ADUs, but like many rural counties in Montana, it has no countywide zoning. ADUs are regulated under statewide ADU laws and standard building/sanitation codes.
Maximum Square Footage:
- Up to 75% of the primary residence or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply in unincorporated areas.
- Only state building code and well/septic separation distances apply.
Please contact the Daniels County Planning Board to verify parcel constraints related to septic, floodplains, or building code requirements.
Does Dawson County Allow ADUs?
Yes. Dawson County allows ADUs, but the county does not administer countywide zoning. ADUs follow Montana’s statewide ADU requirements along with local building, sanitation, and subdivision regulations.
Maximum Square Footage:
- Up to 75% of the primary dwelling or 1,000 sq. ft., whichever is less.
Setbacks:
- No countywide zoning setbacks exist.
- Only building code separation distances, floodplain rules, and sanitation requirements apply.
Please contact the Dawson County Planning Department for site-specific guidance on septic capacity, floodplain limits, or building code compliance.
Does Fallon County Allow ADUs?
Yes. Fallon County allows ADUs, but the county has no countywide zoning, meaning ADUs are governed solely by statewide ADU law and standard building/sanitation regulations.
Maximum Square Footage:
- Less than or equal to 75% of the main dwelling or 1,000 sq. ft., whichever is smaller.
Setbacks:
- No zoning setbacks apply.
- State building code spacing and sanitation separation distances apply instead.
Please contact the Fallon County Planning Department for parcel-specific details, especially regarding septic compliance or well placement.
Does Fergus County Allow ADUs?
Yes. Fergus County allows ADUs, but it does not administer countywide zoning. ADU requirements are therefore dictated by state law and building/sanitation codes unless the parcel lies inside a municipality.
Maximum Square Footage:
- Less than or equal to 75% of the primary dwelling or 1,000 sq. ft. (state limit).
Setbacks:
- No zoning setbacks apply in unincorporated areas.
- Only building/fire code clearances and sanitation separation distances apply.
Please contact the Fergus County Planning Office to confirm building site suitability, septic requirements, and other parcel constraints.
Does Flathead County Allow ADUs?
Yes. Flathead County has zoning in several areas and must allow ADUs by right in those zoning districts under MCA 76-2-345 and SB 532.
Maximum Square Footage:
- Up to 75% of the main home’s floor area or 1,000 sq. ft., whichever is less.
- Larger ADUs may be permitted depending on the zoning district.
Setbacks:
- ADUs cannot face more restrictive setbacks or height limits than the principal dwelling.
- Setback distances vary by zoning district (e.g., R-1, R-2, R-3, etc.).
Please contact the Flathead County Planning & Zoning Department to determine your specific zoning district and confirm applicable development standards.
Does Gallatin County Allow ADUs?
Yes. Gallatin County has adopted zoning in several areas (such as the Gallatin County/Bozeman Area Zoning District), and ADUs must be allowed by right wherever zoning exists.
Maximum Square Footage:
- Up to 75% of the primary residence or 1,000 sq. ft., whichever is smaller.
- Zoning districts may allow additional square footage if stated in the regulations.
Setbacks:
- ADUs may not be subject to stricter setbacks or height limits than the main dwelling.
- Setback distances depend on the zoning district (e.g., Residential, Agricultural, Rural zoning overlays).
Please contact the Gallatin Planning and Community Development to verify zoning coverage and exact placement standards for your property.
Does Garfield County Allow ADUs?
Yes, ADUs are permitted under Montana state law, but Garfield County has no countywide zoning. As a result, ADUs are regulated through statewide ADU law, sanitation approvals, and standard building code requirements.
Maximum Square Footage:
- Less than or equal to 75% of the primary home or 1,000 sq. ft.
Setbacks:
- No zoning setbacks exist.
- Building code spacing, floodplain rules, and septic/well distances apply.
Please contact the Garfield County Clerk & Recorder for septic and property development requirements.
Does Glacier County Allow ADUs?
Yes. Glacier County allows ADUs, but it has no countywide zoning, so ADUs are regulated according to Montana’s statewide ADU laws and local sanitation/building requirements rather than zoning ordinances.
Maximum Square Footage:
- Up to 75% of the primary dwelling’s floor area or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply in unincorporated areas.
- Only building code spacing, floodplain management, and sanitation requirements (well/septic distances) apply.
Please contact the Glacier County Clerk & recorder Department to verify sanitation capacity, floodplain restrictions, and any municipal rules if the parcel falls inside a city boundary.
Does Golden Valley County Allow ADUs?
Yes. Golden Valley County allows ADUs, but the county has no countywide zoning, meaning ADU approval depends on state ADU rules and general building/sanitation requirements.
Maximum Square Footage:
- Less than or equal to 75% of the principal residence or 1,000 sq. ft., whichever is smaller.
Setbacks:
- No zoning setbacks apply.
- Applicable distances come from building code clearances and well/septic separation requirements.
Please contact the Golden Valley County Clerk & Recorder to confirm parcel-specific development requirements.
Does Granite County Allow ADUs?
Yes. Granite County allows ADUs in accordance with statewide law, but the county has no countywide zoning. ADUs therefore follow Montana’s ADU statute along with building, sanitation, and environmental requirements.
Maximum Square Footage:
- Up to 75% of the primary home or 1,000 sq. ft., whichever is less.
Setbacks:
- Since there is no countywide zoning, no zoning setbacks apply.
- State building code spacing, floodplain standards, and sanitation rules govern placement.
Please contact the Granite County Planning Department to verify building site suitability, septic capacity, and floodplain limitations.
Does Hill County Allow ADUs?
Yes. Hill County allows ADUs, but the county has no countywide zoning. ADUs are regulated under state ADU requirements, sanitation approvals, and building codes.
Maximum Square Footage:
- Less than or equal to 75% of the main dwelling or 1,000 sq. ft. (state limitation).
Setbacks:
- No zoning setbacks apply in the unincorporated county.
- Only building/fire code spacing and sanitation separation distances apply.
Please contact the Hill County Planning Department for septic approvals, floodplain maps, and parcel-specific considerations.
Does Jefferson County Allow ADUs?
Yes. Jefferson County allows ADUs, but the county has very limited zoning, and large portions of the county remain unzoned. ADUs are governed primarily by Montana’s statewide ADU law and building/sanitation codes unless a parcel is inside a zoning district.
Maximum Square Footage:
- Up to 75% of the primary dwelling or 1,000 sq. ft., whichever is less.
Setbacks:
- Where zoning exists, ADUs cannot face stricter setbacks or height limits than the main dwelling.
- In unzoned areas, only building code spacing and sanitation distances apply.
Please contact the Jefferson County Planning Department to determine if your property lies within a zoning district and what standards apply.
Does Judith Basin County Allow ADUs?
Yes. Judith Basin County allows ADUs, but the county has no countywide zoning, so ADUs are governed by Montana’s statewide ADU statute and local building/sanitation regulations.
Maximum Square Footage:
- Less than or equal to 75% of the primary home or 1,000 sq. ft.
Setbacks:
- There are no zoning setbacks.
- Only sanitation rules, fire/building code spacing, and floodplain requirements apply.
Please contact the Judith Basin County Clerk & Recorder Office for parcel-specific placement, septic, and infrastructure requirements.
Does Lake County Allow ADUs?
Yes. Lake County allows ADUs, but the county has no countywide zoning, meaning ADUs are regulated primarily through Montana’s statewide ADU law plus county sanitation and building requirements.
Maximum Square Footage:
- Up to 75% of the primary dwelling’s square footage or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply outside incorporated municipalities.
- Placement is determined by building code spacing, floodplain rules, and well/septic separation distances.
Other Requirements:
- No owner-occupancy, design-matching, or additional parking requirements may be imposed under state law.
- ADUs must comply with building, fire, sanitation, and energy codes.
Please contact the Lake County Planning Department for guidance on septic approvals, floodplain constraints, and parcel-specific requirements.
Does Lewis & Clark County Allow ADUs?
Yes. Lewis & Clark County has multiple zoning districts, and ADUs must be allowed by right in those areas under MCA 76-2-345 and SB 532.
Maximum Square Footage:
- Less than or equal to 75% of the primary home or 1,000 sq. ft.
- Some zoning districts (such as more urbanized areas) may allow additional size flexibility.
Setbacks:
- ADUs may not face stricter setbacks or height limits than the main dwelling.
- Actual setback distances depend on your specific zoning district.
Other Requirements:
- No additional parking or owner-occupancy requirements can be imposed.
- ADUs must satisfy Montana’s building, sanitation, fire, and energy code requirements.
Please contact the Community Development and Planning Department to confirm your zoning district and applicable placement standards.
Does Liberty County Allow ADUs?
Yes. Liberty County allows ADUs, but the county has no countywide zoning, so ADUs follow state law along with building and sanitation rules.
Maximum Square Footage:
- Less than or equal to 75% of the main dwelling or 1,000 sq. ft., whichever is smaller.
Setbacks:
- No zoning setbacks apply.
- Only building/fire codes, floodplain regulations, and sanitation distances apply.
Other Requirements:
- No owner-occupancy or parking requirements are allowed under Montana law.
- ADUs must comply with all required building, sanitation, and energy code standards.
This county does not issue local building permits. Therefore, all structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Lincoln County Allow ADUs?
Yes. Lincoln County allows ADUs, but it has no countywide zoning, meaning ADU placement and approval depend on state ADU law, sanitation review, and building code requirements.
Maximum Square Footage:
- Up to 75% of main home area or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks exist in unincorporated areas.
- Only well/septic distances, fire separation distances, and floodplain requirements apply.
Other Requirements:
- No design-style, parking, or owner-occupancy requirements can be added under state law.
- Units must comply with Montana building, sanitation, and energy code provisions.
Please contact the Lincoln County Planning Department to determine sanitation capacity and floodplain restrictions.
Does Madison County Allow ADUs?
Yes. Madison County allows ADUs, but the county does not administer countywide zoning, so ADUs follow statewide ADU laws, along with building and sanitation regulations.
Maximum Square Footage:
- Less than or equal to 75% of the primary home or 1,000 sq. ft., whichever is smaller.
Setbacks:
- No zoning setbacks apply.
- Building, fire safety, floodplain, and sanitation separation distances govern placement.
Please contact the Madison County Planning Office for local infrastructure and septic review requirements.
Does McCone County Allow ADUs?
Yes. McCone County allows ADUs, but the county has no countywide zoning, so ADUs default to state law and local building/sanitation approvals.
Maximum Square Footage:
- Up to 75% of the main residence or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply.
- Only sanitation clearances (well/septic), building code spacing, and floodplain requirements apply.
Other Requirements:
- No parking, architectural, or owner-occupancy requirements may be imposed.
- ADUs must comply with all relevant building, sanitation, and public health regulations.
Please contact the McCone Land Planning Office for parcel-specific development requirements and septic approval procedures.
Does Meagher County Allow ADUs?
Yes. Meagher County allows ADUs, but it has no countywide zoning, meaning ADUs are reviewed under Montana’s statewide ADU statute along with local building, sanitation, and environmental health rules.
Maximum Square Footage:
- Up to 75% of the primary dwelling’s floor area or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply in unincorporated areas.
- ADU placement is governed by building code spacing, floodplain rules, and well/septic separation distances.
Other Requirements:
- No owner-occupancy, architectural matching, or additional parking requirements can be imposed under Montana law.
- ADUs must meet applicable building, sanitation, and energy code standards.
Please contact the Meagher County Consolidated Planning Board for septic reviews, floodplain information, and property-specific requirements.
Does Mineral County Allow ADUs?
Yes. Mineral County allows ADUs, but the county does not administer countywide zoning. ADU approval is based on statewide ADU law plus building, sanitation, and floodplain regulations.
Maximum Square Footage:
- Less than or equal to 75% of the main residence or 1,000 sq. ft., whichever is smaller.
Setbacks:
- No zoning setbacks apply in unincorporated county areas.
- Only building code separations, fire safety spacing, and sanitation distances apply.
Other Requirements:
- No additional parking, design-matching, or owner-occupancy rules may be imposed under MCA 76-2-345.
- ADUs must meet state building code, sanitation, and energy code requirements.
This county does not issue local building permits. Therefore, all structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Missoula County Allow ADUs?
Yes. Missoula County has adopted zoning in many areas, and ADUs must be allowed by right in those zones under Montana’s statewide ADU statute. Zoning standards within the Missoula Urban Growth Area may also apply.
Maximum Square Footage:
- Up to 75% of the primary dwelling or 1,000 sq. ft., whichever is less.
- Some zoning districts may allow more permissive sizes depending on local code updates.
Setbacks:
- ADUs cannot face stricter setbacks, height limits, or lot coverage standards than those applied to the main dwelling.
- Setbacks depend on the specific zoning district (e.g., Residential, Rural, Urban Zones).
Other Requirements:
- No owner-occupancy or additional parking requirements may be imposed under state law.
- ADUs must meet building, fire, sanitation, and energy code standards.
Please contact the Planning, Development and Sustainability for zoning verification and parcel-specific standards.
Does Musselshell County Allow ADUs?
Yes. Musselshell County allows ADUs, but the county has no countywide zoning, so ADU regulation is based on state ADU legislation and local sanitation/building requirements.
Maximum Square Footage:
- Less than or equal to 75% of the principal home or 1,000 sq. ft.
Setbacks:
- No zoning setbacks apply.
- Building code spacing, septic/well distances, and floodplain rules apply instead.
Other Requirements:
- No owner-occupancy, parking, or architectural matching rules are permitted.
- ADUs must comply with Montana codes governing building, sanitation, fire, and energy performance.
This county does not issue local building permits. Therefore, all structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Park County Allow ADUs?
Yes. Park County has zoning in certain areas, meaning ADUs are required to be allowed by right within those zoning districts under Montana’s ADU statute.
Maximum Square Footage:
- Less than or equal to 75% of the primary dwelling’s area or 1,000 sq. ft., whichever is less.
Setbacks:
- Setbacks for ADUs cannot be stricter than those applied to the primary dwelling.
- Actual setback distances are determined by the zoning district (e.g., Rural Residential, Urban Residential).
Other Requirements:
- No extra parking, owner-occupancy, or exterior design-matching requirements may be imposed.
- ADUs must meet Montana’s building, sanitation, and energy code requirements.
Please contact the Park County Planning Department to verify your parcel’s zoning district and applicable ADU requirements.
Does Petroleum County Allow ADUs?
Yes. Petroleum County allows ADUs, but the county has no countywide zoning, meaning ADUs are governed entirely by Montana’s statewide ADU rules and local sanitation/building requirements.
Maximum Square Footage:
- Less than or equal to 75% of the main dwelling or 1,000 sq. ft. (state limit).
Setbacks:
- No zoning setbacks apply.
- Setbacks default to fire/building code spacing, well/septic separation distances, and floodplain considerations.
Other Requirements:
- No owner-occupancy, parking, or architectural-style controls are allowed under state law.
- ADUs must comply with state building, sanitation, fire, and energy codes.
This county does not issue local building permits. Therefore, all structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Phillips County Allow ADUs?
Yes. Phillips County allows ADUs, but the county has no countywide zoning, so ADUs are governed by Montana’s statewide ADU law along with building, sanitation, and subdivision regulations.
Maximum Square Footage:
- Up to 75% of the primary dwelling or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply.
- Placement requirements come from building code spacing, floodplain rules, and well/septic separation distances.
This county does not issue local building permits. Therefore, all structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Pondera County Allow ADUs?
Yes. Pondera County allows ADUs. However, the county has no countywide zoning, so ADUs follow state ADU standards and county sanitation/building requirements.
Maximum Square Footage:
- Less than or equal to 75% of the principal dwelling or 1,000 sq. ft., whichever is smaller.
Setbacks:
- No zoning setbacks apply outside incorporated cities.
- Only building code spacing and sanitation separation distances govern placement.
Other Requirements:
- No additional parking, architectural requirements, or owner-occupancy rules may be imposed under state law.
- ADUs must meet applicable state building, fire, sanitation, and energy codes.
This county does not issue local building permits. Therefore, all structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Powder River County Allow ADUs?
Yes. Powder River County allows ADUs, but it has no countywide zoning, so ADUs rely solely on statewide ADU law and building/sanitation regulations.
Maximum Square Footage:
- Up to 75% of the main dwelling or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply in unincorporated areas.
- Building code spacing, fire safety distances, and well/septic rules apply instead.
Other Requirements:
- No design-style restrictions, parking requirements, or owner-occupancy rules are permitted under MCA 76-2-345.
- ADUs must comply with building, sanitation, fire, and energy codes.
This county does not issue local building permits. Therefore, all structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Powell County Allow ADUs?
Yes. Powell County allows ADUs, but the county has no countywide zoning, so ADU approval is based on statewide ADU law plus building/sanitation/floodplain requirements.
Maximum Square Footage:
- Less than or equal to 75% of the primary home or 1,000 sq. ft., whichever is smaller.
Setbacks:
- No zoning setbacks apply.
- Only sanitation, fire/building code spacing, and floodplain rules govern ADU placement.
Other Requirements:
- No architectural matching, parking, or owner-occupancy requirements may be imposed.
- ADUs must meet Montana’s building, sanitation, and energy code standards.
Please contact the Powell County Planning Department for guidance on permits and code compliance
Does Prairie County Allow ADUs?
Yes. Prairie County allows ADUs, but it has no countywide zoning, so ADUs are approved under statewide ADU law and standard sanitation/building rules rather than zoning standards.
Maximum Square Footage:
- Up to 75% of the main dwelling or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply.
- Building code spacing and well/septic distances govern placement.
Other Requirements:
- No parking or owner-occupancy rules are allowed.
- ADUs must comply with building, fire, sanitation, and energy code requirements.
This county does not issue local building permits. Therefore, all structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Ravalli County Allow ADUs?
Yes. Ravalli County has adopted zoning in several areas, and ADUs must be allowed by right in those zoning districts under Montana’s statewide ADU law (MCA 76-2-345 and SB 532). The county’s Planning Department administers zoning and land-use review for parcels located within these districts.
Maximum Square Footage:
- Up to 75% of the primary dwelling’s floor area or 1,000 sq. ft., whichever is less.
Larger ADUs may be permitted if the governing zoning district specifically allows them.
Setbacks:
- ADUs may not face stricter setbacks or height limits than the primary dwelling.
- Actual setback distances depend on the parcel’s zoning district (e.g., Residential, Rural, or Agricultural zoning).
Other requirements apply, and many vary by zoning district. Please contact the Ravalli Planning & Zoning Commission to confirm which rules apply to your property.
Does Richland County Allow ADUs?
Yes. Richland County allows ADUs, but the county has no countywide zoning, meaning ADUs are regulated according to Montana’s statewide ADU statute together with local building, sanitation, and floodplain requirements. Most ADU approvals in Richland County occur through the Environmental Health/Sanitarian Office.
Maximum Square Footage:
- Up to 75% of the primary dwelling’s floor area or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply in unincorporated areas.
- ADU placement must comply with building/fire code separation distances, well/septic requirements, and any floodplain restrictions.
All structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Roosevelt County Allow ADUs?
Yes. Roosevelt County allows ADUs, but the county has no countywide zoning, meaning ADU requirements come from Montana’s ADU statute and county building/sanitation rules.
Maximum Square Footage:
- Less than or equal to 75% of the primary home or 1,000 sq. ft.
Setbacks:
- No zoning setbacks apply in unincorporated county areas.
- Only well/septic distances, floodplain rules, and building code spacing apply.
Please contact the Roosevelt County Land Planning Department for septic approvals, floodplain issues, and infrastructure considerations.
Does Rosebud County Allow ADUs?
Yes. Rosebud County allows ADUs, but the county has no countywide zoning, meaning ADUs are reviewed under Montana’s statewide ADU law along with building, sanitation, and floodplain requirements.
Maximum Square Footage:
- Up to 75% of the primary dwelling’s floor area or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply in unincorporated areas.
- Building/fire code spacing, floodplain limits, and well/septic separation distances govern placement.
All structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Sanders County Allow ADUs?
Yes. Sanders County allows ADUs, but the county has no comprehensive countywide zoning, so ADUs are governed by statewide ADU law and county sanitation/building rules.
Maximum Square Footage:
- Less than or equal to 75% of the principal residence or 1,000 sq. ft., whichever is smaller.
Setbacks:
- With no zoning ordinance, setbacks are governed by building code spacing, floodplain rules, and sanitation separation distances.
All structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Sheridan County Allow ADUs?
Yes. Sheridan County allows ADUs, but the county has no countywide zoning, so ADU approval falls under statewide ADU law and county building/sanitation regulations.
Maximum Square Footage:
- Up to 75% of the main dwelling or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply in unincorporated areas.
- Building/fire code spacing and sanitation distances determine placement.
Please contact the Sheridan County Commission for specific requirements for your property.
Does Stillwater County Allow ADUs?
Yes. Stillwater County allows ADUs, but it has no countywide zoning, so ADUs depend on Montana’s statewide ADU statute and county sanitation/building/floodplain rules.
Maximum Square Footage:
- Less than or equal to 75% of the primary residence or 1,000 sq. ft.
Setbacks:
- No zoning setbacks exist in the unincorporated areas.
- Only building code spacing, well/septic distances, and floodplain requirements apply.
Please contact the Stillwater County Planning Office to confirm specific rules and guidelines.
Does Sweet Grass County Allow ADUs?
Yes. Sweet Grass County allows ADUs, but the county has no countywide zoning, so ADUs follow statewide law and county sanitation/building requirements.
Maximum Square Footage:
- Up to 75% of the primary dwelling or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply.
- Placement must comply with building/fire code spacing and sanitation requirements.
Please contact the Sweet Grass City-County Planning Office for specific requirements.
Does Teton County Allow ADUs?
Yes. Teton County allows ADUs, but the county has no countywide zoning, so ADUs are regulated under statewide ADU law and building/sanitation requirements.
Maximum Square Footage:
- Less than or equal to 75% of the primary home or 1,000 sq. ft. (state limit).
Setbacks:
- No zoning setbacks apply in unincorporated areas.
- Building code spacing, sanitation distances, and floodplain rules govern placement.
Please contact the Teton County Planning Department to confirm specific requirements for your property.
Does Toole County Allow ADUs?
Yes. Toole County allows ADUs, but the county has no countywide zoning, so ADUs are governed by statewide Montana ADU law along with county sanitation and building requirements.
Maximum Square Footage:
- Less than or equal to 75% of the primary dwelling’s area or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks exist in unincorporated Toole County.
- Building/fire code spacing, floodplain rules, and well/septic separation distances apply.
All structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Treasure County Allow ADUs?
Yes. Treasure County allows ADUs, but it has no countywide zoning, meaning ADUs follow statewide ADU requirements and county building/sanitation standards.
Maximum Square Footage:
- Up to 75% of the principal dwelling or 1,000 sq. ft. (state limit).
Setbacks:
- No zoning setbacks apply.
Placement relies on building/fire code spacing, well/septic requirements, and floodplain regulations.
Please contact the Treasure County Planning Department for specific requirements.
Does Valley County Allow ADUs?
Yes. Valley County allows ADUs, but the county has no countywide zoning, so ADUs are regulated under Montana’s state ADU law plus building, sanitation, and floodplain requirements.
Maximum Square Footage:
- Less than or equal to 75% of the primary dwelling or 1,000 sq. ft., whichever is smaller.
Setbacks:
- No zoning setbacks exist in the unincorporated county.
- Building code spacing, sanitation separations, and floodplain restrictions apply instead.
Please contact the Valley County Planning Department for specific requirements.
Does Wheatland County Allow ADUs?
Yes. Wheatland County allows ADUs, but the county has no countywide zoning, so ADUs rely on statewide ADU law and county sanitation/building regulations.
Maximum Square Footage:
- Up to 75% of the primary home or 1,000 sq. ft., whichever is less.
Setbacks:
- No zoning setbacks apply.
- Setbacks derive from building/fire code spacing and sanitation separation distances.
All structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Wibaux County Allow ADUs?
Yes. Wibaux County allows ADUs, but the county has no countywide zoning, so ADUs are regulated only by statewide ADU law and county sanitation/building requirements.
Maximum Square Footage:
- Less than or equal to 75% of the primary dwelling or 1,000 sq. ft.
Setbacks:
- No zoning setbacks apply.
- Placement must satisfy fire/building code spacing, well/septic distances, and floodplain requirements.
All structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Does Yellowstone County Allow ADUs?
Yes. Yellowstone County has zoning in certain areas, and ADUs must be allowed by right in those zoning districts under Montana state ADU law.
Maximum Square Footage:
- Up to 75% of the primary residence or 1,000 sq. ft., whichever is less.
Certain zoning districts may permit larger ADUs depending on local standards.
Setbacks:
- ADUs cannot be held to stricter setbacks or height limits than the main home.
- Exact setback distances depend on the zoning district (e.g., Agricultural, Suburban Residential, Urban Residential).
All structural and building-code requirements are handled by the Montana Building Codes Program. Please consult their office for guidance on permits and code compliance.
Which Cities in Montana Allow ADUs?
Thanks to statewide legislation (SB 528, codified at §76-2-345, MCA), Montana cities must allow at least one accessory dwelling unit (ADU) by right on any lot with a single-family home, with a maximum size of the lesser of 1,000 sq. ft. or the floor area of the primary dwelling.
Below are 10 of Montana’s larger cities with links to their planning/building offices and a brief summary of how each handles ADUs. Please note that townships and boroughs often enforce their own regulations, so be sure to check with them to ensure compliance.
Montana Cities & Contacts
Does Belgrade, MT, Allow ADUs?
Yes, but you must meet specific requirements, including:
Size:
- Rural Zone & Suburban Residential Zone: ADU may be attached or detached and is limited to a maximum of 1,000 sq. ft.
- Neighborhood Zone: ADU must be attached to the main dwelling or located above a detached garage and is limited to a maximum of 800 sq. ft.
Permitted Zoning Districts:
- Rural Zone and Suburban Residential Zone (attached or detached ADUs)
- Neighborhood Zone (attached or over-garage ADUs)
- Mixed Use Center, Commercial Corridor, Downtown District, Flex Employment, and Industrial zones (one ADU per lot for an owner, manager, guard, or caretaker)
Be sure to take all necessary steps to get your structure approved with the Belgrade Building Department.
Does Billings, MT, Allow ADUs?
Yes, but you must meet specific requirements, including:
Size:
- Detached ADU: Up to 75% of the primary dwelling’s gross floor area or 1,000 sq. ft., whichever is less
- Attached ADU: Up to 80% of the primary dwelling’s gross floor area or 1,000 sq. ft., whichever is less
(From the 2025 Billings City/County Planning Division code interpretation.)
Permitted Zoning Districts:
- N1 – Neighborhood 1
- N2 – Neighborhood 2
- N3 – Neighborhood 3
(ADUs allowed by right wherever a single-family dwelling is permitted in these districts.)
Be sure to take all necessary steps to get your structure approved with the Billings City/County Planning Division.
Does Bozeman, MT, Allow ADUs?
Yes, but you must meet specific requirements, including:
Size:
- Subject to the statewide ADU size cap: if the ADU is attached or detached, it may not exceed 75% of the gross floor area of the single-family dwelling or 1,000 sq. ft., whichever is less, plus any additional limits in Bozeman’s Unified Development Code.
Permitted Zoning Districts:
- The Bozeman Municipal Code provides that any parcel on which a single-household detached dwelling will be constructed is permitted to construct an accessory dwelling unit, either within the primary building or in a freestanding accessory building, in compliance with §38.360.040.
Be sure to take all necessary steps to get your structure approved with Bozeman Community Development.
Does Butte-Silver Bow, MT, Allow ADUs?
Yes, but you must meet specific requirements, including:
Size:
- In the consolidated city-county of Butte–Silver Bow, ADUs must comply with Montana Code §76-2-345, which caps attached or detached ADUs at no more than 75% of the gross floor area of the single-family dwelling or 1,000 sq. ft., whichever is less, along with any additional limits in local zoning regulations.
Permitted Zoning Districts:
- ADUs are administered under the Butte–Silver Bow zoning ordinance; specific districts and standards are set in local land use regulations for parcels with single-family dwellings.
Be sure to take all necessary steps to get your structure approved with the Butte–Silver Bow Planning Department.
Does Great Falls, MT, Allow ADUs?
Yes, but you must meet specific requirements, including:
Size:
- ADUs in Great Falls must meet the statewide size standard in Montana Code §76-2-345, which limits attached or detached ADUs to no more than 75% of the gross floor area of the single-family dwelling or 1,000 sq. ft., whichever is less, in addition to any local standards in the City’s Land Development Code (Title 17).
Permitted Zoning Districts:
- ADU permissions are implemented through the City of Great Falls Land Development Code (Title 17) and applied through the zoning and permitting process for lots with single-family dwellings.
Be sure to take all necessary steps to get your structure approved with Great Falls Planning & Community Development.
Does Helena, MT, Allow ADUs?
Yes, but you must meet specific requirements, including:
Size:
- If the ADU is detached from or attached to the single-dwelling unit, it may not be more than 75% of the gross floor area of the single-dwelling unit or 1,000 sq. ft., whichever is less, as set out in Helena City Code draft §11-4-5.
Permitted Zoning Districts:
- ADUs are regulated in Title 11, Chapter 4 (District Dimensional Standards) of the Helena City Code and are reviewed in conjunction with the zoning district applicable to the lot.
Be sure to take all necessary steps to get your structure approved with the City of Helena Planning Division.
Does Kalispell, MT, Allow ADUs?
Yes, but you must meet specific requirements, including:
Size:
- An ADU may not exceed 1,000 sq. ft. in size under Kalispell Zoning Ordinance §27.20.082.
Permitted Zoning Districts:
- ADUs are allowed as a permitted use on a single lot in the following zones: R-4, R-5, RA-1, RA-2, H-1, B-1, B-2, B-3, and B-4, either as a duplex or as a principal structure plus an accessory dwelling unit, subject to the conditions in §27.20.082.
Be sure to take all necessary steps to get your structure approved with the Kalispell Planning Department.
Does Livingston, MT, Allow ADUs?
Yes, but you must meet specific requirements, including:
Size:
- ADUs must comply with the statewide standard in Montana Code §76-2-345 (maximum 75% of the gross floor area of the single-family dwelling or 1,000 sq. ft., whichever is less) and the detailed standards for accessory dwellings adopted in Livingston Municipal Code Chapter 30 (including recent amendments by Ordinance 3056).
Permitted Zoning Districts:
- ADUs are governed by the City of Livingston zoning ordinance (Chapter 30); specific districts and dimensional standards are applied through the Building & Planning review process.
Be sure to take all necessary steps to get your structure approved through the Livingston Building & Planning Department.
Does Missoula, MT, Allow ADUs?
Yes, but you must meet specific requirements, including:
Size:
- ADUs cannot be larger than 600 square feet under Missoula’s ADU standards in Title 20.
Permitted Zoning Districts:
- ADUs are allowed on parcels occupied by a single detached house in all Residential, Business, Commercial, and Limited Industrial-Residential (M1-R) zoning districts under Missoula’s zoning ordinance (Title 20).
Be sure to take all necessary steps to get your structure approved with Missoula Development Services.
Does Whitefish, MT, Allow ADUs?
Yes, but you must meet specific requirements, including:
Size:
- An ADU may be up to 1,000 sq. ft. or 75% of the size of the main house, whichever is smaller.
Permitted Zoning Districts:
- ADUs are allowed in all zoning districts accessory to a single-family residence, subject to applicable setback and lot-coverage rules.
Be sure to take all necessary steps to get your structure approved with the Whitefish Planning & Building Department.
Searching for an ADU Builder Serving Montana?
If ADUs are allowed in your Montana, the next step is to find a trustworthy ADU builder you can partner with. Zook Cabins is pleased to offer our experience and skills to make your dream ADU become a reality. Contact us and talk to a sales representative or request a free quote to move the process ahead.
We understand how hard it can be to choose a reliable company that prioritizes your satisfaction. That’s why we promise transparent pricing, a commitment to project completion, and an excellent work ethic. Choose Zook Cabins today and watch your vision of the ideal ADU unfold from start to finish.
Tiny Home & ADU Rules By State: See How They Compare?
In some cases, park model tiny homes can be used as ADUs, while in others, they can’t. As you’ve come to learn, this really depends on where you live. If you’re interested in using a park model tiny home as an ADU, but aren’t sure where it’s allowed, you can use the chart below to check out tiny home regulations across the U.S., including in MT.