State ADU law
Montana ADU laws: one ADU by right in every city
Montana’s 2023 law (SB 528) gives every city and town lot with a house the right to one ADU.
What to do next: use this research to check your own lot and bids, then tell us about your project. Matching is not live yet, so we reply with information, not a quote.
Get ADU optionsWritten by HyreADU Research Desk Primary-source statute research
The short answer
Montana ADU laws require every city and town to allow at least one accessory dwelling unit by right on any lot with a single-family home. MCA 76-2-345 lets the ADU be attached, detached or inside the house.
An attached or detached unit may be up to 75% of the house’s floor area or 1,000 square feet, whichever is less. A city may not require extra parking, owner-occupancy, matching design, or impact fees.
It may charge a one-time application fee of up to $250 per ADU, plus its usual building fees. Local rules that conflicted with the statute became void on January 1, 2024.
What Montana law requires of cities
Each row is from MCA 76-2-345 (En. Sec. 1, Ch. 502, L. 2023) as published in the Montana Code Annotated 2025.
| Question | What the Montana statute says | Citation |
|---|---|---|
| Must the city allow ADUs? | Yes. At least one ADU by right on a lot with a single-family home. “By right” means no hearing, variance or conditional use permit. | MCA 76-2-345(1)(a), (9)(b) |
| Attached, detached or internal? | Any of the three. | MCA 76-2-345(1)(b) |
| Size? | An attached or detached ADU may be up to 75% of the house’s gross floor area or 1,000 square feet, whichever is less. | MCA 76-2-345(1)(c) |
| Parking? | A city may not require more parking or fees in lieu of parking. | MCA 76-2-345(2)(a) |
| Owner-occupancy? | Banned. Nor may a city require a family or employment link between occupants. | MCA 76-2-345(2)(c)–(d) |
| Design, height, setbacks? | No matching design rule. Height, setback, lot size and coverage rules may not be stricter than for the house. | MCA 76-2-345(2)(b), (g) |
| Fees? | No impact fees. A one-time application fee of up to $250 per ADU is allowed, plus usual building fees. | MCA 76-2-345(2)(e), (4) |
| Utilities? | A city may require a will-serve letter from the municipal water and sewer systems. | MCA 76-2-345(7) |
Montana ADU rules set by state law, as read on the official statute page on October 27, 2026.
Who the law covers and when it took effect
The rule applies to incorporated cities, towns and consolidated city-counties that zone under Title 76, chapter 2, part 3 (MCA 76-2-345(9)(d)). Unincorporated county land is not covered by this section.
Cities that had not updated their rules by January 1, 2024 must review ADUs under the statute until they do, and conflicting local rules in effect on or after that date are void (MCA 76-2-345(5)).
What is still up to your city or county
Cities can still regulate short-term rentals (MCA 76-2-345(3)) and apply building, fire and health codes (subsection 6). They can be more permissive than the statute (subsection 8).
Private covenants between neighbors still bind, but a city may not make a permit depend on one (subsection 2(i)). Check your deed and any HOA rules separately.
How to check your own city
Answer these in order, in writing, before you pay for drawings.
- 1 Confirm you are inside city or town limits
MCA 76-2-345 covers municipalities. County land follows county zoning.
- 2 Get the will-serve letters
Ask the water and sewer utilities first. A city may require both.
- 3 Check your house’s gross floor area
An attached or detached ADU is capped at 75% of it, or 1,000 square feet if less.
- 4 Ask for the application fee in writing
The statute caps the ADU application fee. Building permit fees are separate.
- 5 Read your deed and HOA covenants
Private covenants are not voided by this law.
What this page does not cover
This page covers the Montana statute only. It does not cover building codes, septic and well rules, HOA covenants, flood or wildfire overlays, or your city’s fee schedule. Those can still stop a project the statute allows.
We read the statute on October 27, 2026. Laws change, and courts read them.
If your project depends on one clause, have a land-use attorney or the planning department confirm it for your parcel.
For the national picture, see which states have ADU laws; for what to ask at the counter, see the ADU permit guide.
Questions
Can I build an ADU in Montana without a hearing?
How big can an ADU be in Montana?
Do Montana cities charge impact fees on ADUs?
Does Montana require owner-occupancy for an ADU?
Written and audited by
HyreADU Research Desk
Primary-source research, data analysis and fact checking
We are a research desk, not a builder. We read the permit extract, the statute, the HCD return or the fee schedule ourselves, and publish each figure with its source and retrieval date.
Where a number cannot be traced to a primary source, we leave it out and say what we could not verify. Our store-based claims cover California only.
- CA
- the only state this desk will make store-based claims about
- 5
- jurisdictions with extracted ADU permit evidence
- 735
- CSLB-verified companies in the California store
- 0
- national claims from a one-state store
How this desk works
- Primary sources only. Permit counts come from the city or county that issued the permit. Production counts come from HCD’s Annual Progress Report. Rents come from HUD or the Census. We do not cite an article that cites a source; we download the source and compute the figure ourselves.
- This is a California site. The company store is 734 California firms and one New Mexico firm. Permit evidence exists for five named jurisdictions: Los Angeles, San Francisco, Sacramento, San José and unincorporated Marin. A number from that store is titled to those places, never to the United States.
- A permit is not a completion, and a license is not an ADU grade. California licenses no ADU classification. Being named on an ADU permit is evidence of engagement in that jurisdiction, not of quality, completion, or work anywhere else. Owner-builder permits are excluded from contractor counts.
- Calculation is labeled as calculation. Figures we derive are never presented as something HCD, HUD, the Census or a city published. Terner Center research is cited as Terner’s, never restated as ours.
- We do not design, permit or build ADUs, and we take no payment for placement, ranking or a favorable mention. Pages that look like rankings are not: they publish public-record counts and let the reader decide.
- Nothing here is legal, tax or financial advice. Zoning, underwriting and appraisal practice vary by jurisdiction, lender and appraiser. The useful next step on a specific lot is the planning counter and a licensed professional.
Data as of MCA 76-2-345 read on leg.mt.gov (Montana Code Annotated 2025), retrieved 2026-10-27.. Authorship on this site is organizational: the analysis belongs to the desk rather than to a named individual, and we do not publish credentials we do not hold.
Our editorial policy sets out how we source, date and correct what we publish.
Sources & retrieval dates
- MCA 76-2-345, Accessory dwelling units, regulations, restrictions , Montana Code Annotated 2025, Montana Legislature Retrieved October 27, 2026.
Planning an ADU in Montana?
Tell us about your lot and what you want to build. Matching is not live yet, so this is not a quote. We will send ADU options and the next questions to ask your city.
HyreADU is a publisher. It does not design, permit or build ADUs, and matching with builders is not live yet. This page describes state statutory text as published on the retrieval date.
It is not legal advice. Your city or county applies the rules to your lot, and its planning department is the authority for your parcel.