Montana ADU Laws

Complete 2026 guide to accessory dwelling unit regulations

✓Strong Statewide Law

📋Quick Facts

Max Size
1,000 sq ft
Size Limit
75% of primary
Owner Occupancy
✓ Not required
Parking
✓ Limited by state
Approval Process
✓ By-right
Effective Date
1/1/2023

📜Recent Legislation

76-2-345 MCA (2023) - Statewide ADU mandate requires municipalities to allow minimum one ADU by right on single-family lots

⚠️Key Requirements & Restrictions

  • •Max 75% of primary dwelling floor area OR 1,000 sqft, whichever is less
  • •Cannot set parking requirements or fees in lieu of parking
  • •Cannot require owner-occupancy
  • •Cannot assess impact fees on ADU construction
  • •Max $250 application fee allowed

📖Detailed Analysis

Strong statewide ADU law 76-2-345 MCA enacted 2023. Municipalities must allow minimum one ADU by right on single-family lots. Law explicitly prohibits many common restrictions: parking requirements, owner-occupancy mandates, impact fees, architectural matching requirements. Cities that hadn't adopted compliant regulations by Jan 1, 2024 must review/permit under state standards. Law preserves local authority for building/fire/health codes and utility requirements.

🔗Official Resources

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⚠️ Disclaimer

The information provided on this website is for general informational purposes only and does not constitute legal, financial, or professional advice. ADU laws, regulations, and requirements vary by jurisdiction and change frequently. While we strive to keep this information accurate and up-to-date, we make no representations or warranties of any kind about the completeness, accuracy, reliability, or suitability of this information. Always consult with qualified local professionals, including attorneys, architects, and your local planning department, before making any decisions regarding ADU construction or investment. Use of this information is at your own risk.

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Last updated: February 2026