ADU Zoning in Boston, MA
Complete ADU zoning guide for Boston, Massachusetts. Learn about allowed ADU types, approval process, size limits, and local zoning regulations.
Boston's Local ADU Ordinance
Unlike most Massachusetts municipalities, Boston operates under its own zoning charter with ADU-specific rules that may differ from the state baseline. This means some state-level rights may not apply in the same way. Check the specific rules below for Boston's requirements.
By-Right Approval: No Hearing Required
ADUs in Boston are approved by right. This means you submit your building plans to the building department and receive a building permit without going through a public hearing or special permit process. By-right approval significantly reduces both the timeline and cost of your ADU project.
Allowed ADU Types
Boston allows the following ADU types: detached, attached, conversion. Detached ADUs are standalone structures in your yard — the most flexible option. Attached ADUs share a wall with your existing home, reducing construction costs. Interior conversions transform existing space (basement, attic, or garage) into a separate dwelling unit.
Owner Occupancy: A Family-Focused Investment
Boston requires that the property owner live in either the main house or the ADU. While this limits pure investment use, it makes ADUs ideal for multi-generational families — house aging parents in the ADU while keeping them close, or give adult children an affordable first home on the family property.
Historic District Considerations
Boston has historically significant areas including Boston National Historical Park - Charlestown Navy Yard, Boston's Old City Hall, Faneuil Hall Marketplace, Historic Boston Inc, Old State House. If your property is located within or adjacent to a historic district, your ADU design may need to go through additional design review to ensure compatibility with the neighborhood's architectural character. This can affect exterior materials, rooflines, and window styles. Consult with the local historical commission early in your planning process.
Important: State Baseline Data
The information on this page reflects Massachusetts state baseline rules. Boston may have additional local requirements. We recommend confirming with your local building department before starting your project.
Boston ADU Rules at a Glance
Max Size
1250 sq ft
% of Home
75%
Max Height
25 ft
Max Stories
2
Front Setback
25 ft
Side Setback
5 ft
Rear Setback
5 ft
Parking
1 space(s)
Approval
BY RIGHT
Owner Occupancy
Required
Rental Allowed
Yes
Short-Term Rental
Not allowed
Boston Building Department
Boston Inspectional Services Department
1010 Massachusetts Ave # 5, Boston, MA 02118, USA
Phone: (617) 635-5300
Frequently Asked Questions
Are ADUs allowed by right in Boston, MA?
Yes. ADUs in Boston are approved by right — you submit your plans to the building department and receive a building permit without a public hearing or special permit process. This is set by Boston's local zoning ordinance.
What types of ADUs can I build in Boston?
Boston allows detached, attached, conversion ADUs. With up to 1250 sq ft allowed, a detached ADU gives you the most flexibility for a full living space.
Do I have to live on the property to have an ADU in Boston?
Yes, Boston requires owner occupancy — you must live in either the main house or the ADU. This makes ADUs in Boston an especially strong long-term investment for families looking to house aging parents nearby or provide a first home for adult children while generating rental income from the other unit.
How big can I build an ADU in Boston, MA?
In Boston, you can build an ADU up to 1250 square feet or 75% of your home's living area, whichever is larger. With 1250 sq ft, you have enough room for a full 2-bedroom cottage with a kitchen, bathroom, and living area. This is set by Boston's local zoning ordinance.
Does Boston have historic district rules for ADUs?
Yes. Boston has historically significant areas including Boston National Historical Park - Charlestown Navy Yard, Boston's Old City Hall, Faneuil Hall Marketplace, Historic Boston Inc, Old State House. If your property is in or near a historic district, your ADU design may require review by the local historical commission for architectural compatibility. This can affect timelines and design choices.
Can I rent out my ADU in Boston?
Yes, long-term rentals are allowed for ADUs in Boston. However, short-term rentals (like Airbnb) are not currently allowed for ADUs. With a population of 675,647, Boston has strong rental demand.
How accurate is the ADU data for Boston?
The information on this page reflects Massachusetts state baseline rules under the Affordable Homes Act. Boston may have additional local requirements that differ from the state baseline. We recommend confirming with your local building department before starting your project.
Check Your Address
See exactly what ADU rules apply to your specific property in Boston.