State ADU Laws
Plain-language summaries of statewide ADU laws, updated quarterly. Each guide covers maximum size, setbacks, owner-occupancy requirements, and permit timelines.
California has the most permissive ADU laws in the United States. State law preempts most local ADU restrictions, requiring cities to allow ADUs on virtually any single-family lot.
Massachusetts passed historic statewide ADU legislation in 2024 as part of the Affordable Homes Act, allowing ADUs by-right on single-family lots in most municipalities.
Washington's HB 1337 (2023) is one of the strongest ADU laws in the country, requiring cities of 25,000+ to allow at least two ADUs per lot in most residential zones.
Oregon was a national pioneer in ADU policy. HB 2001 requires cities of 25,000+ to allow ADUs on single-family lots; Portland alone has permitted thousands.