In plain words

Montana requires most cities, towns and zoned counties to allow ADUs. An ADU (accessory dwelling unit) is a second, smaller home on the same lot as a house. It can be inside the house, attached to it, or a separate cottage. Since 2024, every city or town with zoning must allow at least one ADU with a single-family home. Zoning means the local rules about what can be built where. Since October 2025, counties with county zoning must do the same. Approval is by right. That means no public hearing, no special permit and no vote, as long as the ADU meets the written rules. Your town cannot require you to live on the property. It cannot charge impact fees, which are one-time charges for roads and services. It cannot make the ADU match your house's look. The review fee is capped at $250, plus normal building permit fees. In cities, an attached or detached ADU can be 1,000 square feet or 75% of the house, whichever is smaller. Cities cannot require an extra parking space. Counties can, because the county law is silent on parking. Towns can still regulate short-term rentals. Much rural land in Montana has no zoning at all, so building, well and septic permits matter most there. Bigger cities that switch to the state's newer planning law may follow that law instead. Those cities also cannot require parking for small homes starting October 2026. A lawsuit challenged these rules. The Montana Supreme Court upheld them in March 2026. You still need permits, and your lot must work for an ADU.

The rules at a glance

State ADU lawYes
Where the state rule appliesAll incorporated cities, towns and consolidated city-counties that zone under the municipal zoning part of the code (SB 528), and county areas where the county commissioners have adopted zoning under the county zoning part of the code, MCA Title 76 ch. 2 part 2 (SB 532). Unzoned rural land has no zoning to override. Larger cities that move to the Montana Land Use Planning Act fall under that Act instead (see local_control_notes).
Approved without a hearing?Yes. Qualifying ADUs are approved by staff review, without a discretionary hearing.
Kinds of ADU the state protectsinternal, attached, detached
ADUs per lotAt least 1 ADU per lot with a single-family home (local governments may allow more)
Owner living on siteTowns can’t require the owner to live on the property.
ParkingCities and towns may not require extra parking or a fee in lieu of parking for an ADU. The 2025 county law does not mention parking, so counties are not barred from requiring it. From 2026-10-01, cities under the Montana Land Use Planning Act may not require any parking for homes under 1,200 sq ft (HB 492, 2025), which covers city ADUs there.
SizeCities: an attached or detached ADU may be no larger than 75% of the house's floor area or 1,000 sq ft, whichever is less (no cap stated for internal ADUs). Counties: no square-foot cap in statute. In both, an ADU must be smaller than the main house by definition.
Lot size and setbacksCities and zoned counties may not set height limits, setbacks, minimum lot sizes, lot coverage limits or frontage rules for an ADU that are stricter than for the house on the same lot, and may not add other more burdensome development standards.
FeesNo impact fees may be charged on an ADU. The ADU application review fee is capped at $250 per unit, plus the usual building permit fees. Cities may require will-serve letters from city water and sewer.
Short-term rentalsCities and counties may still regulate short-term rentals, including in ADUs.
Can towns opt out?No

What to do next

  1. Find out who zones your property: a city or town, a county zoning district, or no one; your county planning office can tell you.
  2. If you are in a city, check the 1,000 sq ft / 75% size cap and ask whether the city has adopted a new code under the Montana Land Use Planning Act (Missoula and Bozeman have).
  3. Ask for the ADU application fee in writing; state law caps the zoning review fee at $250 per ADU and bars impact fees.
  4. Line up water and sewer early: cities may ask for will-serve letters, and lots with public water and sewer can get a 15-day state sanitation review in zoned counties.
  5. If you plan to rent short term, read the local short-term rental rules, which still apply to ADUs.
  6. Check your deed or HOA covenants; state law stops towns from requiring ADU covenants but does not cancel private ones.

What your town still decides

Montana leaves a lot of land unzoned, especially in rural counties; there the state ADU rule has nothing to override, and building and septic permits are the main hurdles. Where zoning exists, ADU approval must be by right, which state law defines as no public hearing, no variance or conditional use permit, and no other discretionary vote. The 2025 county rule is written for zoning adopted under the county zoning part of the code (part 2); citizen-initiated planning and zoning districts created under part 1 are not named in it. One wrinkle: under MCA 76-25-105(4), a city that complies with the Montana Land Use Planning Act is not subject to the older zoning chapter where the SB 528 ADU rule sits. Under that Act, allowing an internal or detached ADU is one of fourteen housing options a city can pick (it must pick at least five), though from October 2026 such cities also may not require parking for homes under 1,200 sq ft. Missoula and Bozeman, both covered by the Act, adopted new codes that took effect in early 2026; Bozeman's allows ADUs on single-home lots, and Missoula's is reported to build in the 2023 state housing requirements. A 2023 lawsuit by a homeowner group against the ADU, duplex and planning laws failed: the Montana Supreme Court lifted an injunction on 2024-09-03 and upheld the laws unanimously in March 2026.

Examples of local rules

  • Missoula: Replaced its zoning with a Unified Development Code (Title 22), adopted February 2, 2026 and fully in effect March 4, 2026. Local reporting says the new code builds in the 2023 state housing requirements. Before that, the city had already removed ADU parking requirements and allowed renters or family in either unit. Check Title 22 for current ADU size and placement rules. Source
  • Bozeman: Replaced its Unified Development Code (Chapter 38) through Ordinance 2151, given final adoption on December 16, 2025 and effective February 1, 2026. The new code allows ADUs on single-home lots, removes minimum lot sizes and reduces residential parking requirements. Source

What we’re still confirming

  • Whether the state's ADU guarantee still applies in cities that have switched to the Montana Land Use Planning Act is unsettled.
  • Ask your city whether it has finished switching to the Land Use Planning Act; the general deadline was May 17, 2026.

Laws, bills and citations

The laws behind this (4)
  • Limits on city parking requirements (HB 492 (2025), Laws of 2025 ch. 682 (amends MCA 76-2-304 and 76-25-303), signed May 13, 2025, in effect October 1, 2026). Not ADU-specific. Cities zoning under the Montana Land Use Planning Act may not require any parking for homes under 1,200 sq ft, which closes the parking gap for ADUs in cities that left the older zoning chapter. Other zoned cities may not require more than half a space for homes under 1,200 sq ft (their ADUs were already exempt from extra parking). It does not apply to county zoning. Read it
  • County zoning must allow ADUs (SB 532 (2025), Laws of 2025 ch. 619; MCA 76-2-215 (amends MCA 76-4-130), signed May 12, 2025, in effect October 1, 2025). Requires counties that have adopted county zoning to allow at least one attached, detached or internal ADU by right on any lot with a single-family home. Counties may not require owner occupancy, matching design, impact fees, street improvements, or stricter height, setback, lot-size or coverage rules than for the house. It sets a $250 cap on the ADU application fee and creates a 15-day state sanitation review for ADUs on lots with public water and sewer. Read it
  • City and town zoning must allow ADUs (SB 528 (2023), Laws of 2023 ch. 502; MCA 76-2-345, signed May 17, 2023, in effect January 1, 2024). Requires every incorporated city, town and consolidated city-county with zoning to let every lot with a single-family home have at least one ADU by right. Attached and detached ADUs can be up to 75% of the house's floor area or 1,000 sq ft, whichever is less. Cities may not require extra parking, owner occupancy, matching design, impact fees or street improvements, and may charge at most $250 to review the application. Read it
  • Montana Land Use Planning Act (ADU option on a housing menu) (SB 382 (2023), Montana Land Use Planning Act, Laws of 2023 ch. 500; MCA 76-25-105 and 76-25-302, signed January 1, 2023, in effect May 17, 2023). Requires cities of 5,000 or more people in counties of 70,000 or more to adopt at least five of fourteen housing strategies. One option is allowing at least one internal or detached ADU as a permitted use on a lot whose house is someone's primary residence; another is cutting ADU impact fees. Cities that comply with this Act are no longer governed by the older zoning chapter that contains the SB 528 ADU rule. Read it
Proposed and failed bills (1). None of these is law.
  • HB 802 (2025): died as of October 3, 2026. Would have stopped local bans on rentals, including short-term rentals, from applying to an owner's primary home, an ADU on the same lot, or a home on an adjoining lot. It was tabled in committee on March 4, 2025 and died after missing the transmittal deadline. Bill page

Sources

  1. HB 492 (2025), Laws of 2025 ch. 682 (amends MCA 76-2-304 and 76-25-303) · official source
  2. SB 532 (2025), Laws of 2025 ch. 619; MCA 76-2-215 (amends MCA 76-4-130) · official source
  3. SB 528 (2023), Laws of 2023 ch. 502; MCA 76-2-345 · official source
  4. SB 382 (2023), Montana Land Use Planning Act, Laws of 2023 ch. 500; MCA 76-25-105 and 76-25-302 · official source
  5. MCA 76-2-215 Accessory dwelling units, county zoning (Montana Code Annotated 2025) · official source · checked 2026-10-03
  6. MCA 76-25-105 Applicability and compliance (MLUPA) · official source · checked 2026-10-03
  7. 2023 Land Use Legislation summary, Montana Legislative Fiscal Division · official source · checked 2026-10-03
  8. Governor Gianforte praises Montana Supreme Court ruling upholding pro-housing reforms (2026-03-17) · official source · checked 2026-10-03
  9. Montanans Against Irresponsible Densification v. State, DA 24-0039 (Mont. Sept. 3, 2024) · checked 2026-10-03
  10. Daily Montanan: Montana Supreme Court said zoning laws meant to ease housing crisis are valid (2026-03-18) · checked 2026-10-03
  11. MTFP Capitol Tracker 2023: SB 528 · checked 2026-10-03
  12. MTFP Capitol Tracker 2025: SB 532 · checked 2026-10-03
  13. HB 802 (2025) introduced bill text · official source · checked 2026-10-03
  14. MTFP Capitol Tracker 2025: HB 802 status · checked 2026-10-03
  15. Missoula Unified Development Code (Title 22) · official source · checked 2026-10-03
  16. Missoula ADU FAQs (Engage Missoula) · official source · checked 2026-10-03
  17. Missoula near-term code amendments for 2023 state legislation · official source · checked 2026-10-03
  18. Bozeman UDC adoption draft, December 2025 · official source · checked 2026-10-03
  19. Bozeman Daily Chronicle: Bozeman provisionally adopts UDC increasing zoning density · checked 2026-10-03
  20. MCA 76-25-303 Limitations on zoning authority (MLUPA; version effective 2026-10-01) · official source · checked 2026-10-03
  21. MTFP Capitol Tracker 2025: HB 492 (signed 2025-05-13) · checked 2026-10-03
  22. City of Bozeman: Unified Development Code adopted (Ordinance 2151) · official source · checked 2026-10-03

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.