ADU Rules: Belmont vs Somerville
How do adu rules rules compare between Belmont, MA and Somerville, MA?
Belmont and Somerville have similar restriction levels.
Belmont, MA
Middlesex County
Under the 2024 MA Affordable Homes Act (MGL c.40A s.3A), ADUs up to 900 sq ft are allowed by-right on every single-family lot in Middlesex County. No owner-occupancy or special permit required.
View full Belmont rules →Somerville, MA
Middlesex County
Somerville was an early Massachusetts adopter of ADU zoning and now complies with the 2024 Affordable Homes Act mandating ADUs by right in all single-family zones statewide.
View full Somerville rules →Key Facts Comparison
| Fact | Belmont | Somerville |
|---|---|---|
| State Law | MGL c.40A s.3A (Feb 2025) | - |
| Max Size | 900 sq ft or 50 percent | - |
| Owner-Occupancy | Not required | - |
| Parking Max | 2 spaces max | - |
| Review Type | By-right, no special permit | - |
| State mandate | - | Affordable Homes Act 2024 |
| Max size | - | 900 sq ft by right |
| Owner occupancy | - | Not required |
| Parking mandate | - | Prohibited by state |
| Permit | - | Building permit required |
Highlighted rows indicate differences between cities.
Belmont FAQ
Can I build an ADU on my lot in Middlesex County?
Yes. As of February 2025, the Affordable Homes Act requires all MA municipalities to allow ADUs by right on single-family lots up to 900 sq ft.
Do I have to live on the property?
No. The statewide ADU law prohibits owner-occupancy requirements, so you can rent both units.
Somerville FAQ
Can I build a backyard ADU in Somerville?
Yes. ADUs up to 900 sq ft are allowed by right under state law and Somerville zoning.
Do I need to live on the property?
No. Owner occupancy cannot be required under the 2024 Affordable Homes Act.
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