Accessory Structures in Billings, MT

If you live in Billings or are thinking about moving there, accessory structures are one of those things you probably won't think about until they affect you directly. Billings has 3 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.

ADU Owner Occupancy

Billings requires the property owner to live in either the main house or the ADU at least six months a year, with a recorded deed restriction.

Key details: Owner-occupancy minimum: 6 months per year. Deed restriction required: Recorded with Yellowstone County. Third-party rentals: Barred in owner-occupied unit. By-right districts: N1, N2 (N3 needs special review).

Renting both units to third parties without owner-occupancy, or skipping the recorded deed restriction, puts the ADU out of compliance with the zoning approval and can trigger code enforcement action by the Planning and Community Services Department.

Shed & Carport Rules

Billings zoning caps detached accessory buildings like sheds and shops at 1,500 square feet once they pass 200 square feet, and bars building in a required setback or within 5 feet of another structure.

Key details: Size cap over 200 sq ft: 1,500 sq ft or house footprint. Building setback: min. 5 ft from another building. Combined cap, N1/N2/N3/RMH: 2,000 sq ft total. Timing rule: not more than 180 days early. Enforcement: municipal infraction, civil penalty.

Violations are a municipal infraction with civil penalties under BMCC Sec. 18-1300, or a misdemeanor; the zoning coordinator can also issue a stop-work order or withhold permits. Each day of noncompliance counts as a separate offense.

ADU Rules

Billings allows one accessory dwelling unit per residential lot by right in N1/N2 zones, by special review in N3, with owner-occupancy and size caps.

Key details: Units allowed: 1 per residential lot. By-right zones: N1, N2 (special review in N3). Min. lot size: 3,000 sq ft. Max detached size: 80% of primary or 750 sq ft. Occupancy rule: Owner in primary or ADU 6+ months/yr.

Building an ADU without planning approval or exceeding the size/height caps is a zoning violation subject to the city's standard code enforcement and permit-revocation process under the Unified Development Code.

The Bottom Line

Billings's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Billings is broadly strict or permissive.

These rules come from Billings's publicly available municipal code. For complete penalty schedules, exemption details, and answers to common questions, see the individual ordinance pages throughout this guide.