■ STATE BY-RIGHT + PARCELS ■
ADU Rules in Massachusetts
Massachusetts allows one ADU up to 900 sq ft (or half the main home's floor area, whichever is smaller) by right in single-family districts statewide, effective February 2025. Cities and towns may regulate ADUs but cannot prohibit them or require owner-occupancy.
LAW: Affordable Homes Act (Acts of 2024, Ch. 150) · PRIMARY SOURCE
// OUR DATA HERE
Parcel lookups run on MassGIS statewide public records. Town-level dimensional rules are being added on top of the state baseline.
// FAQ
Massachusetts ADU Questions
Are ADUs legal in Massachusetts?
Yes — statewide. Since February 2025, the Affordable Homes Act makes one ADU up to 900 sq ft (or half the principal home's floor area) a by-right use in single-family zoning districts across Massachusetts.
Can my town block my ADU in Massachusetts?
Towns can apply reasonable regulations (site plan review, dimensional standards) but cannot prohibit a by-right ADU or impose owner-occupancy requirements under the 2024 state law.
How big can a Massachusetts ADU be?
The state by-right protection covers ADUs up to 900 sq ft or half the principal dwelling's gross floor area, whichever is smaller. Larger units may still be allowed under local zoning.