ADU rules in Belgrade

Detached ADUs are a permitted accessory use on single-family lots in every district except Open Space & Parks and the two Airport districts (Table 10.3.4 marks ADU P in the other 12 districts, subject to 10-3-39). In the Rural and Residential Suburban zones the code expressly allows an ADU attached or detached from the main dwelling. The Neighborhood Residential zone text says an ADU shall be attached or located above a detached garage, but MCA 76-2-345 (binding on municipalities since 1-1-2024) guarantees one attached, detached, or internal ADU by right on any lot with a single-family dwelling and voids more onerous local standards, so a fully detached backyard ADU cannot be refused on that basis. In the Mixed Use, Commercial Corridor, Downtown, Flex Employment, and Industrial districts the allowance is framed as one ADU per lot for an owner, manager, guard, or caretaker.

Attached and above-garage ADUs are allowed wherever ADUs are permitted. The Rural and Residential Suburban zones allow attached or detached units; the Neighborhood Residential zone allows attached units or units above a detached garage; 10-3-39.E lets an ADU be added above an existing garage if structurally viable. One ADU is allowed per single-family lot, with a kitchen, bathroom facilities, and at most two bedrooms, and it must meet the size, height, setback, and lot coverage rules of its district.

10-3-39.C caps ADUs at 1,000 sq ft in the Rural and Residential Suburban zones and 800 sq ft in the Neighborhood Residential zone; no ADU-specific cap is written for the Mixed Residential, Community Living, or commercial districts, and every ADU is limited to two bedrooms. MCA 76-2-345(1)(c) entitles each single-family lot to an ADU of up to 75% of the gross floor area of the single-family dwelling or 1,000 square feet, whichever is less, and voids stricter local rules, so the 800 sq ft Neighborhood cap cannot cut below that statutory line for a larger home. Detached ADUs also fall under the general accessory-structure rules of 10-3-38 (at most two accessory buildings per lot and a cumulative 1,000 sq ft accessory ground-floor area in residential districts, with a not-taller-than-the-house height rule), though 76-2-345(2)(g) bars applying height, setback, or coverage standards to an ADU that are stricter than the primary dwelling's.

No owner occupancy may be required, but the unamended code still prints the requirement. Belgrade's 10-3-39.B.6 reads: the property owner shall occupy either the primary dwelling or accessory dwelling unit as their principal residence. MCA 76-2-345(2)(c) forbids a municipality to require that the single-family dwelling or the ADU be occupied by the owner, and subsection (5) declares non-compliant ADU regulations in effect on or after 1-1-2024 void. The ADU section has not been amended since adoption (Ord. 2023-7, 7-17-2023), so the printed text and operative law diverge; the statute controls, and the Montana Supreme Court definitively upheld the ADU statute in March 2026 (MAID v. State, 2026 MT 53).

MCA 76-2-345(2)(a) bars municipalities from requiring additional parking to accommodate an ADU or fees in lieu, and subsection (5) voids non-compliant regulations. Belgrade's ADU section nonetheless still reads that one paved off-street parking space shall be provided for the exclusive use of the ADU in addition to the principal dwelling's parking (10-3-39.D), and it conditions garage-to-ADU conversions on meeting parking minimums for both units (10-3-39.E.1). Both provisions date to Ord. 2023-7 (7-17-2023), have never been amended, and are void as applied to ADUs; parking requirements for the primary dwelling itself are unaffected.

ADU review is administrative. Table 10.6.7 (Specific Uses Permit Staff Level Approval) routes an ADU through a Building Permit plus a Land Use Application, with the Community Development Director as the final decision-making authority and the Building Official commenting; the Director must approve, conditionally approve, or disapprove within 90 days of a complete application (10-6-15.F). ADUs do not appear in the public-hearing table (10.6.8) and need no conditional use permit in any district, which matches MCA 76-2-345's by-right mandate (no hearing, no discretionary action beyond site-plan conformance, application fee capped at $250 plus normal building fees). Interim Zoning Ordinance 2026-6 (July 2026) shifts former Planning Board and Board of Adjustment roles to the new MLUPA Planning Commission but leaves staff-level ADU review unchanged.

Nothing in the ADU section restricts renting the unit long-term, and the printed owner-occupancy rule that would have tied rentals to an on-site owner is void under MCA 76-2-345(2)(c). Short-term rentals are a defined residential use: any dwelling or portion rented for under 30 consecutive days is an STR, allowed in residential districts and mixed-use districts within residential units, which covers ADUs; RVs may not be used as STRs. An STR requires a Short-Term Rental Permit (10-6-8), a city STR license under Title 2 (Business and License Regulations), and registration with the Montana Department of Revenue (10-3-47.A); city guidance adds a fire inspection and a Gallatin City-County Health Department public accommodations license. MCA 76-2-345(3) expressly preserves this local STR regulation. The code has no separate-sale provision; an ADU remains accessory to its single-family lot.