ADU Laws in Montana (2026)
Montana state ADU law details, key provisions, preemption status, and recent legislative changes for accessory dwelling units.
Law Name
Montana HB 245 (2023) — Montana Zoning Act Reforms
Effective Date
2023-10-01
Preempts Local Ordinances
Yes — state law overrides local restrictions
Has State Law
Yes
Key Provisions
Montana HB 245 requires municipalities to allow ADUs by right in all residential zones · Source
ADUs must receive ministerial approval — no discretionary review, variance, or special use permit required for qualifying ADUs · Source
Municipalities may not impose owner-occupancy requirements on ADU applicants · Source
Local regulations may set reasonable dimensional standards (setbacks, height, size limits) but cannot ban ADUs · Source
Montana HB 245 was part of a broader package of housing supply legislation passed in the 2023 session · Source
Montana HB 337 (companion bill) reformed large-scale zoning restrictions for middle housing types · Source
Montana's rapid growth in cities like Bozeman, Missoula, and Billings created urgent housing supply needs driving this legislation · Source
Legislative History
2023 — See official source
Montana required municipalities to allow ADUs by right in residential zones. Part of the landmark 2023 Montana housing reform session that also included HB 337 (middle housing), SB 382 (streamlined permitting), and other supply-side measures. Effective October 1, 2023. · Source
2023 — See official source
Companion to HB 245 — required municipalities to allow middle housing types (duplexes, triplexes, townhouses) in residential zones previously limited to single-family use. Montana became one of the first states to pair ADU reform with missing middle housing reform. · Source
Official Sources
What Does Preemption Mean for Local Cities?
Because Montana law preempts local ordinances, individual cities cannot impose restrictions stricter than the state standard. A city may still have additional administrative requirements, but cannot deny ADU applications that comply with state minimums.
Learn about Montanazoning preemption →Source: Montana HB 245 (2023) — Montana Zoning Act Reforms. Last verified April 5, 2026. View source