Accessory Structures in Montana (2026)
10 rules on the books across Montana, 2 cities and counties. Select a rule to read the full details.
Severity: Few Restrictions · Light Restrictions · Some Restrictions · Significant Restrictions · Heavy Restrictions
ADU Rules
Rules for building accessory dwelling units (granny flats, in-law suites) including size limits, parking requirements, and owner-occupancy rules.
Montana: statewide
StatewideFew RestrictionsMontana SB 528, codified in 2023, requires cities and counties to allow accessory dwelling units on lots zoned for…
Read full rule →Billings
Some RestrictionsBillings allows one accessory dwelling unit per residential lot by right in N1/N2 zones, by special review in N3, with…
Read full rule →Yellowstone County
Some RestrictionsIn Yellowstone County's zoning area around Billings, "accessory living quarters" (guest houses) are allowed within an…
Read full rule →ADU Owner Occupancy
Whether the property owner must live on-site to operate an ADU, deed-restriction requirements, and recent state-law changes lifting owner-occupancy rules.
Yellowstone County
Significant RestrictionsIn unincorporated Yellowstone County, an accessory dwelling unit only gets approved if the property owner actually…
Read full rule →Billings
Some RestrictionsBillings requires the property owner to live in either the main house or the ADU at least six months a year, with a…
Read full rule →Shed & Carport Rules
When a storage shed or carport needs a permit, the square-footage exemption thresholds, and the setback and height limits that apply either way.
Billings
Some RestrictionsBillings zoning caps detached accessory buildings like sheds and shops at 1,500 square feet once they pass 200 square…
Read full rule →Yellowstone County
Some RestrictionsYellowstone County's zoning ordinance has no separate carport standard; a carport is treated as an accessory building…
Read full rule →Garage Conversions
Rules for converting a garage into living space, including whether you need to replace the lost parking and what building codes apply.
Tiny Homes
Zoning rules for tiny houses on wheels and foundations, including minimum square footage requirements and where they can be placed.
Montana: statewide
StatewideSome RestrictionsMontana adopts statewide building and residential codes through the Department of Labor and Industry. Tiny houses on…
Read full rule →Yellowstone County
Heavy RestrictionsYellowstone County's zoning code will not let a mobile home, manufactured home, RV, travel trailer, or any other…
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