Rules by State
/ Montana
Montana MT ADU Rules
Last updated: April 2025 · Reviewed by ADU Journal editorial team
ADU Friendliness Score
28
★ Restrictive
Size & Dimensions
Max ADU Size (Detached)
Determined locally
Max ADU Size (Attached)
Determined locally
Min ADU Size
Determined locally
JADU Max Size
Not recognized statewide
Max Height (Detached)
Determined locally
Stories Allowed
Determined locally
Setbacks & Lot Coverage
Rear Setback
Determined locally
Side Setback
Determined locally
Front Setback
Determined locally
Minimum Lot Size
Determined locally
Fire Sprinklers
Determined locally
Owner Occupancy & Rental Rules
Owner Occupancy Required?
Locally Regulated
Short-Term Rental (Airbnb)
Determined locally
Rental Income Allowed?
Yes
ADUs Per Lot
Determined locally
No statewide standard
Permitting Process
Review Timeline (Ministerial)
Determined locally
Permit Fees
Determined locally
Design Review Required?
Determined locally
Preapproved Plans Available?
No statewide program