Accessory Dwelling Units (ADUs) in Brookline, MA
Brookline is one of the many Massachusetts communities adapting to new state requirements that expand housing access through Accessory Dwelling Units (ADUs). With recent zoning changes and the statewide Affordable Homes Act, it's now easier for homeowners to add in-law units, backyard cottages, or basement apartments.
Here’s what you need to know about building an ADU in Brookline as of 2025.
Statewide ADU Regulations: The Affordable Homes Act
In 2024, Massachusetts passed the Affordable Homes Act, which requires all cities and towns to allow at least one ADU by right on residential properties with up to four units—not just single-family homes.
Key provisions include:
ADUs allowed by right in all residential zoning districts for 1–4 unit properties
No special permit required if the ADU meets zoning and building code standards
No owner-occupancy requirement
No additional parking required if the property is within 0.5 miles of public transit
Towns cannot limit ADUs to single-family homes or impose additional permitting burdens on compliant units
If your ADU qualifies as a “protected use,” it’s shielded from local restrictions that go beyond these statewide rules.
Brookline's Local ADU Policies
Brookline has revised its local zoning to allow ADUs by right, in compliance with the Affordable Homes Act. The town’s updated policies include:
One ADU allowed by right on lots with up to 4 residential units
Maximum size: 900 square feet or 50% of the gross floor area of the main dwelling (whichever is smaller)
Design standards: ADUs must match the architectural style of the principal dwelling and preserve the look of a single-family home
Separate entrance required, either directly or through a shared hallway
No additional parking required for ADUs near public transit
Brookline also allows both internal and detached ADUs, making it possible to convert existing garages or basements into legal units.
Community Sentiment & Local Implementation
Brookline residents have voiced mixed but evolving views on ADUs. Supporters cite the need for more flexible housing options, especially for multigenerational living, aging in place, and creating modest rental income. Town meeting members and planning officials have generally embraced ADUs as a low-impact way to expand the housing supply.
That said, some residents have expressed concerns about density, parking, and neighborhood character. As a result, Brookline has worked to ensure its local design standards help new ADUs blend with existing homes, while still meeting state requirements for by-right approval.
The town has also emphasized that enforcement and communication will be key to successful ADU implementation moving forward.
What This Means for Homeowners in Brookline
If you own property in Brookline, the path to building an ADU is now more accessible than ever. You may be eligible to add an ADU by right, without going through a special permit process, provided your unit meets baseline requirements.
Before moving forward, make sure to:
Confirm your zoning district and lot size
Plan for proper egress, utilities, and code compliance
Review Brookline’s local building requirements (especially for detached structures)
Get a Custom ADU Roadmap for Your Property
Considering building an ADU in Brookline? We offer a comprehensive ADU Roadmap Report tailored to your property. It includes:
On-site visit and feasibility analysis
Cost and timeline estimates
Full permitting guidance
Rental comps and income projections
Referrals to vetted contractors and architects
👉 Schedule Your ADU Roadmap Consultation
Note: For the most accurate and up-to-date information, refer to Brookline’s Planning Department or reach out for a personalized evaluation.
