MT SB266

Cities with populations of at least 5,000 must allow duplex, triplex, and fourplex housing as permitted uses on any lot where single-family residences are permitted, with zoning regulations no more restrictive than those for single-family homes.

Local governments are prohibited from denying the use of duplexes, triplexes, or fourplexes on lots where single-unit dwellings are permitted, or adopting more restrictive zoning for these housing types.

Urban areas over 5,000 population with municipal water and sewer must allow multiple-unit dwellings and mixed-use developments in commercial zones, with parking limited to one off-street space per unit plus ADA-required accessible spaces.

The bill removes "allow duplex where single-unit dwelling is permitted" from the list of optional housing strategies local governments can choose from, making it a mandatory requirement instead.

Effective date is October 1, 2026.