ADU Rules in Somerville, MA
Somerville follows the Massachusetts state baseline with local regulations.
HIGH Confidence Data
MA
State Baseline: Affordable Homes Act
Up to 900 sq ft or 50% of principal dwelling (whichever is smaller). By-right approval statewide.
Zoning Districts
NR — Neighborhood Residential
Low-density neighborhood residential
Default Zone
| Type | Approval | Max Size | Height | Parking | Owner Occ. |
|---|---|---|---|---|---|
| Detached ADU | By Right | 900 sq ft | 15 ft | None | No |
| Attached ADU | By Right | 900 sq ft | 25 ft | None | No |
| Interior Conversion | By Right | 900 sq ft | — | None | No |
UR — Urban Residential
Medium-density urban residential
| Type | Approval | Max Size | Height | Parking | Owner Occ. |
|---|---|---|---|---|---|
| Detached ADU | By Right | 900 sq ft | 15 ft | None | No |
| Interior Conversion | By Right | 900 sq ft | — | None | No |
Transit Stations
Properties near transit stations may qualify for parking exemptions.
Ball Square
SUBWAY
Davis
SUBWAY
East Somerville
SUBWAY
Gilman Square
SUBWAY
Magoun Square
SUBWAY
Somerville (future)
COMMUTER RAIL