ADU Rules: Brookline vs Wellesley

Can I build an ADU on my property in Brookline?

Brookline updated its ADU bylaw (§ 4.05) in 2024 to comply with MGL c. 40A §3. One ADU by right on single-family lots is allowed up to 900 sq ft or 50% of principal floor area. Owner-occupancy requirements removed. FAR cap for ADUs eliminated.

What are the size limits for an accessory dwelling unit in Brookline?

Code Section: Brookline ZO § 4.05 (2024 amendment). Maximum Size: 900 sq ft or 50% of principal GFA. Owner-Occupancy: No longer required. Parking: Max 1 space; exempt within 0.5 mi of transit.

Are detached ADUs allowed by-right in Wellesley?

Yes, as of April 15, 2025. The Massachusetts Attorney General approved Wellesley's Article 40.1 bylaw amendment, removing the Special Permit requirement for detached ADUs in Single Residence Districts. A building permit and annual Certificate of Compliance are still required.

How big can a Wellesley ADU be?

Under §5.13 and the MA Affordable Homes Act (G.L. c. 40A as amended), an ADU is capped at 900 sq ft or 50% of the primary dwelling's gross floor area, whichever is smaller.

Does Wellesley require an annual filing for ADUs?

Yes. Wellesley §5.13 requires an annual Certificate of Compliance (Notice of Accessory Unit) from the Planning Department in addition to the initial building permit from the Inspector of Buildings.