Building permits, zoning and septic rules in Stillwater County, Montana

Stillwater County does not operate a certified local building-code program, so Montana handles building permits and inspections for projects under state building-code jurisdiction^1,7. Montana requires state building permits for nonexempt buildings; exemptions include farm and ranch buildings, private homes and apartments with four or fewer units that do not serve transient guests, and private storage buildings and garages². Separately, Stillwater County requires a conditional-use permit before new multifamily, work-camp, commercial, industrial or planned-unit construction begins³. Qualifying agricultural uses do not require that county development permit, but septic permits, floodplain development permits, access requirements and applicable state building permits remain separate^8,10,11. Ask Planning to classify the use; for a state building permit, submit plans and the application to the Montana Building Codes Program^7,10.

Direct state building-permit and inspection questions to the Montana Building Codes Program because Stillwater County has no certified local building-code program^1,7. Start county land-use and conditional-use-permit questions with the Stillwater County Planning Office at 431 Quarry Road, Columbus, MT 59019, or 406-322-8050¹. Planning routes submitted forms to Environmental Health, the Floodplain Administrator, GIS/Rural Addressing, and Road & Bridge when needed¹². Stillwater County Environmental Health handles county septic construction authorization and inspections, but septic systems are prohibited inside Columbus town limits^5,6. Floodplain development permits go through the Floodplain Administrator, and county-road encroachment-permit applications go to Road & Bridge^1,13.

Stillwater County's development and zoning regulations govern unincorporated land outside the City of Columbus extra-territorial zoning jurisdiction and state and federal land⁸. Columbus sets its own zoning, including an extra-territorial area shown on its zoning map; County Planning administers county and Columbus subdivision regulations^4,10. Septic systems are prohibited inside Columbus town limits⁵. Stillwater County sets no general setback for residential property, but development requiring a conditional-use permit must be set back at least half the structure’s height, with minimums of 10 feet at the front and 5 feet at the sides and rear^1,8. For a newly subdivided parcel with individual water and sewer, at least one acre of buildable land must lie outside the delineated floodway, and every lot needs at least 30 feet of frontage on its access street or road¹⁴. Those are subdivision standards, not a general minimum lot size for every existing parcel¹⁴. Countywide rules for RV living, tiny homes, minimum dwelling size and lot coverage could not be confirmed; ask Planning about the exact parcel and use.

Stillwater County septic construction requires DEQ or county sanitation approval first: properties under 20 acres require a DEQ Certificate of Subdivision Approval, and properties over 20 acres require county sanitary approval⁶. Ask Environmental Health which approval applies to a parcel of exactly 20 acres⁶. Obtain county construction authorization before installation; the published septic-system permit fee is $200^6,15. The contractor must request inspection before 3 p.m. the preceding day, and the sanitarian issues the septic permit after a compliant inspection⁶. Inspection or licensed-installer verification is required before covering the system; confirm the accepted procedure with Environmental Health^11,16. Only 7.6% of county soils lack severe limitations for conventional drain fields, so obtain a site evaluation early¹⁷. Off-grid wastewater systems, including gray-water disposal, require authorized-consultant design and county approval; holding tanks, outhouses and porta-potties are prohibited⁶. Septic systems are prohibited inside Columbus town limits⁵.

Stillwater County's general rules for residential or long-term RV occupancy and tiny-home occupancy could not be confirmed; ask Planning about the exact parcel, structure and duration. Within a regulated flood-hazard area, an RV may stay without a floodplain permit for fewer than 180 consecutive days only if it remains licensed and highway-ready, uses quick-disconnect utilities, has no permanent additions, and requires no structures, fill, grading or excavation⁹. That floodplain exception does not establish that residential RV use is allowed by zoning or other law⁹. A tiny home or RV still needs an approved wastewater solution: consultant-designed gray-water disposal needs county approval, while holding tanks, outhouses and porta-potties are prohibited⁶. Countywide rules for minimum dwelling size, temporary camping, manufactured homes also could not be confirmed; put the exact proposal in writing to Planning.

1. Ask Planning which jurisdiction controls the parcel and whether the proposed use needs a county conditional-use permit^3,10.

1. Ask the Floodplain Administrator whether the site is regulated; grading, fill, excavation and construction in a regulated flood-hazard area require a floodplain development permit¹⁰.

1. Obtain DEQ or county sanitation approval, then county septic construction authorization through Environmental Health; schedule inspection before backfilling^6,16.

1. Before using a qualifying exempt well, file the required Notice of Intent; uses over 35 gallons per minute or 10 acre-feet per year require a water permit¹⁸.

1. Ask the Montana Building Codes Program which state building, plumbing and other trade permits and inspections apply^2,7. A homeowner personally doing plumbing in a personal residence may be exempt from the plumbing permit if the home is neither speculative construction nor a rental¹⁹.

1. Confirm legal and physical access; county conditional-use review requires legal and physical access and may require road-maintenance agreements or bonding, while a state-highway approach needs MDT approval^8,20.

Make septic suitability, legal access, flood status and water rights purchase contingencies. Only 7.6% of Stillwater County soils are rated without severe limitations for conventional drain fields, so obtain a site evaluation before treating a homesite as buildable¹⁷. A qualifying exempt well requires a Notice of Intent before use, and groundwater use over 35 gallons per minute or 10 acre-feet per year requires a water permit¹⁸. Ask the Floodplain Administrator about the exact building area because grading, excavation, fill and construction in regulated flood-hazard areas require a floodplain development permit¹. Confirm whether access meets a county road or state highway because county encroachment permits and state-highway approach permits have different authorities^13,20. Ask Planning about land-division review, including certificate-of-survey and exempt divisions; the published survey-review fee is $200^1,10. New lots with individual water and sewer also have buildable-area and road-frontage standards¹⁴.