Montana residential & ADU permit data

Montana enacted statewide accessory-dwelling-unit reform as part of the 2023 'Montana Miracle' housing package. Senate Bill 528 (2023), codified at section 76-2-345 of the Montana Code, requires every municipality to adopt regulations allowing at least one ADU on any lot or parcel that already contains a single-family dwelling, effective January 1, 2024. The statute is aimed squarely at the usual obstacles — it constrains the owner-occupancy mandates, off-street-parking minimums and impact fees that cities had used to make backyard units impractical.

SB 528 travels with SB 323 (2023), which requires municipalities of more than 5,000 residents to allow duplexes wherever single-family homes are permitted, under standards no stricter than those applied to a single-family house. Together they ended single-family-only zoning across Montana's larger cities while guaranteeing an ADU option in every municipality in the state.

The reforms survived an immediate legal fight. A group called Montanans Against Irresponsible Densification won a preliminary injunction in district court, but the Montana Supreme Court reversed that injunction in 2024 — finding the challengers had not met the burden for emergency relief — which let SB 528 and SB 323 take effect, and a district court later sustained the laws on the merits. The 2025 legislature then revisited the framework, with Senate Bill 532 building on and revising the original SB 528 ADU rules, so the details continue to evolve session to session.

Montana's approach is broader in reach than most reform states even if its city sizes are small: like California, Washington and Oregon it guarantees ADUs by right statewide, but the ADU duty reaches every municipality rather than only larger or transit-served cities, and it is paired with a duplex mandate that kicks in above 5,000 residents. That is a sharper break from pure local control than the targeted, big-city-only mandates in Colorado and Arizona. Igni sources live Bozeman permit data from the city's open-data portal, so new ADU and duplex activity surfaces as the statewide rules bed in across one of the fastest-growing housing markets in the Mountain West.

This is an informational summary, not legal advice; each city's adopted regulations control the specifics and the statute was amended in 2025, so verify the current law before relying on it.