ADU rules in Bozeman

Bozeman repealed and replaced its entire Chapter 38 Unified Development Code by Ordinance 2151 (adopted 12-16-2025, effective 2-1-2026) under the Montana Land Use Planning Act. In the new code an ADU, defined as 'an accessory residential building, either attached or detached, which contains a dwelling unit', is a permitted accessory use with standards (A*) in every residential district (R-A, R-B, R-C, R-D) plus REMU, NEHMU, M-1 and M-2; each residential district's intent statement lists ADUs among the housing types the district is meant to accommodate. One ADU is allowed per lot. The one bite: detached ADUs (including units above detached garages) 'may be approved only if found compatible and consistent with the existing character and fabric of the neighborhood', an administrative design-compatibility finding that attached ADUs do not face. A detached ADU may not exceed 25 feet in height but may be taller than the principal dwelling.

The ADU definition covers 'either attached or detached' accessory residential buildings, and the standards allow ADUs attached to or above garages; the Planned Development Zone provisions likewise describe ADUs 'either within the primary building or in a freestanding accessory building', so internal conversions count as the attached form. Attached and internal ADUs follow the same Table 38.320.120.B-1 standards (one per lot, size cap, no deviations) but are not subject to the neighborhood-compatibility design finding that applies only to detached ADUs. The addition of an ADU on an infill lot is expressly excused from full compliance with minimum density standards (sec. 38.260.030).

Table 38.320.120.B-1: 'In no case may an ADU be larger than 1,000 square feet or 75% of the principal unit, whichever is larger', measured as the sum of habitable and occupiable spaces under the adopted building code. The larger-of formula is deliberately more generous than the floor set for non-MLUPA cities by MCA 76-2-345(1)(c), which caps ADUs at 75% or 1,000 sq ft 'whichever is less'; on a 2,400 sq ft house Bozeman allows an 1,800 sq ft ADU. Height: a detached ADU may exceed the principal building's height but not 25 feet; no accessory building may exceed the footprint of the principal building (38.320.120.A.5).

The ADU standards table has no occupancy or ownership row, and the only owner-occupancy rule anywhere in the new Chapter 38 is in the bed-and-breakfast definition; nothing requires the owner to live in either unit, and no familial relationship is required. While Bozeman zoned under MCA Title 76 ch. 2, state law (76-2-345(2)(c)) barred owner-occupancy mandates outright; the city's MLUPA-based code continues without one even though that bar no longer directly applies (76-25-105(4)). The one occupancy tie that remains is for short-term rental only: renting the ADU as an STR requires the host's primary residence on the same lot (Type-2B).

Table 38.320.120.B-1: 'ADUs are not subject to minimum parking requirements. If parking is provided it must conform to all applicable standards.' The catch is garage conversions: 'Garages may not be converted for use as ADUs unless all required parking for all uses on the lot is otherwise provided prior to conversion', though building an ADU above a garage is fine. The no-parking rule carried over from the SB 528 era (MCA 76-2-345(2)(a) barred ADU parking minimums for ch. 2 cities) and Bozeman kept it in the 2026 MLUPA rewrite even though the statutory bar no longer directly binds it.

ADUs are an accessory use ('A', not 'S' special use) in the allowed use table, and 'Accessory dwelling units' appear on the sketch plan list (38.740.060.A.3.d): a staff-level review that 'may be conducted as part of building permit review or as an independent application'. Sketch plans go to the community development department 'for a determination of compliance with the requirements of this chapter. Once compliance is achieved, the application will be approved for construction'; no public hearing or conditional use permit is involved. Two frictions: detached ADUs need the review authority's neighborhood-compatibility finding (Table 38.320.120.B-1), and inside the neighborhood conservation overlay a certificate of appropriateness is required for accessory structures unless exempt (38.320.120.A.7).

Nothing restricts renting an ADU on ordinary leases, and no owner-occupancy or familial tie applies. Short-term rental (under 28 consecutive days) requires a city hosting permit: an ADU STR is classified Type-2B, 'a short term rental of an accessory dwelling unit (ADU) on the same lot as the host's primary residence', so an investor who lives elsewhere cannot STR the ADU. Zone limits apply: in the R-A district only Type 1 STRs (bedrooms in the host's occupied home) are allowed, so ADU STRs are effectively unavailable there (use table as corrected by City Attorney Order 2026-01 per Ord. 2149); Types 1 and 2 are allowed in R-B, R-C, R-D, most business districts, REMU and NEHMU. Dedicated non-primary-residence STRs (old Type 3) have been banned citywide since Ordinance 2149 took effect 12-14-2023; pre-2023 permitted Type 3s survive only as legacy permits.