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 on any lot where a single dwelling is permitted or already exists, as long as the lot holds at least 3,000 square feet. The ADU is capped at 80 percent of the main home's floor area or 1,000 square feet, whichever is less, and it can never be sold separately from the primary dwelling or lot.

Key details: Minimum lot size: 3,000 square feet with a primary home and an ADU. ADUs per lot: One, on the same lot as the primary unit. Maximum ADU size: 80 percent of the principal home or 1,000 sq ft, whichever is less. Required facilities: Kitchen or food prep area, bathroom and sleeping area. Banned structures: Mobile homes, RVs, travel trailers, wheeled structures.

Under Section 27-1704(G), violating the zoning code is a misdemeanor, and each day the violation continues counts as a separate offense. The zoning coordinator can also withhold or revoke permits, issue a stop work order that names the code section violated, or order a use stopped. Owners, contractors and occupants who control the property can be held jointly responsible under Section 27-1703. Aggrieved parties can appeal final administrative land use decisions under Section 27-1616.

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.