Building permits, zoning and land rules in Big Horn County, Montana

A single-family home in unincorporated Big Horn County generally does not need a state building permit where no local ordinance requires one¹. In state jurisdiction, the exemption covers residential buildings with fewer than 5 dwelling units except when serving transient guests, plus farm and ranch buildings and private garages or storage buildings used by the owner outside a business². Hardin has a certified residential building-code program within city limits⁴.

Montana adopted the 2024 International Building and Residential Codes effective September 26, 2026; a state building-permit exemption does not establish an exemption from separate electrical, plumbing or mechanical permits^1,14. Owner-work is exempt from the construction-contractor chapter, subject to a restriction on improvements intended for prompt resale; the exemption does not waive building, trade or health requirements¹⁰.

Big Horn County is not listed as a certified countywide building-code program, so the Montana Building Codes Program handles nonexempt work outside listed local jurisdictions⁴. Hardin handles residential building-code enforcement inside city limits⁴. Start with the Big Horn County Commissioners for parcel-specific subdivision, setback, RV, tiny-home or minimum-size questions that remain unconfirmed^7,9.

For nonexempt construction under Montana's jurisdiction, submit construction plans and a Building Permit/Plan Review Application to the Montana Building Codes Program². The state issues a building permit after plan-review comments are resolved and required fees are paid, and separate trade permits may still be needed². For projects requiring a state building permit, the permit holder must notify the state inspector when work is ready for inspection⁸.

Big Horn County’s planning-area description identifies no zoning other than a wireless-communications-facilities ordinance². Subdivision regulations still apply in the unincorporated county planning area, so confirm subdivision approval and recorded conditions with the County Commissioners before planning a home^7,9. The planning-area description does not establish current countywide setbacks or minimum-home-size rules; ask the Big Horn County Commissioners about the specific parcel⁹.

Inside city limits, Hardin has its own zoning, so the county planning-area description is not the city’s zoning answer³. Septic permitting remains with Big Horn County Public Health countywide, including city addresses needing an onsite system⁵.

Big Horn County Public Health's sanitarian administers septic permitting countywide⁵. Send a written request with the address, property description and current owner, then submit the application and fee; requests should arrive two weeks before the desired site visit⁵. If a site visit is needed, the process may require an eight-foot-deep hole within 25 feet of the proposed drainfield⁵. Installation cannot begin until the sanitarian issues the permit to construct⁵.

Big Horn County requires a final inspection before burial and an installer report before the operating permit; the report is due within 10 days after inspection⁵. Montana DEQ subdivision sanitation approval does not replace the local drainfield permit¹⁵. Only 8.3% of mapped soils are rated without severe limitations for a conventional drain field, so make wastewater feasibility an early purchase contingency¹⁶. Ask Environmental Health before choosing a nonstandard sanitation system because we could not confirm countywide rules for off-grid alternatives¹⁷.

We could not confirm a Big Horn County rule allowing full-time RV occupancy or a tiny home as a permanent dwelling on private land; ask the Big Horn County Commissioners whether subdivision conditions, setbacks or minimum-home-size rules affect the parcel, and ask Environmental Health how the proposed occupancy must handle wastewater^5,7,9.

A tiny home used as a single-family residence may fit the rural building-permit exemption when no local ordinance requires a permit, but septic and trade requirements remain separate¹. Hardin's residential building-code program applies inside city limits⁴. For owner-installed plumbing in state jurisdiction, the homeowner exemption requires personal use and excludes rental property or speculative resale¹¹.

1. Ask the Big Horn County Commissioners whether subdivision review, recorded conditions, setbacks or other parcel-specific controls apply^7,9.
2. For a rural single-family home, confirm the state exemption and any separate trade permits; inside Hardin, contact the city about its residential building-code program^1,4.
3. Send the septic request early, then obtain the county permit to construct before installation and arrange inspection before burial⁵.
4. Ask the Floodplain Administrator whether county floodplain regulations and the permit requirement for a designated hazard area affect the site^6,12,13.
5. Ask the county Roads office about local access; a new or modified approach to a state highway needs a state approach permit or right-of-way agreement^18,19.

Start with wastewater feasibility because only 8.3% of mapped soils avoid severe conventional-drainfield limitations, and a local drainfield permit remains necessary even when Montana DEQ has approved subdivision sanitation^15,16. For a proposed well under Montana’s water-permit exception, file a Notice of Intent with DNRC before using the water; eligibility is not automatic²⁰.

Check the plat and subdivision conditions with the County Commissioners because subdivision regulations apply in the county planning area^7,9. Check floodplain status before planning fill, roads, excavation, a manufactured home or other development in a designated hazard area^6,12,13. Verify legal access with the Roads office, and use Montana's separate approval path when a driveway meets a state highway^18,19. For carrying costs, the effective property-tax rate is about 1%, and the median annual tax bill is $1,482¹⁶.