ADU Zoning in Somerville, MA
Complete ADU zoning guide for Somerville, Massachusetts. Learn about allowed ADU types, approval process, size limits, and local zoning regulations.
ADU Regulations in Somerville
Somerville follows the Massachusetts state baseline under the Affordable Homes Act. This means all Massachusetts state-level ADU rights apply — including by-right approval, no owner occupancy requirement, and standardized size limits. Somerville may also have additional local regulations that supplement the state baseline.
By-Right Approval: No Hearing Required
ADUs in Somerville 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
Somerville 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.
No Owner Occupancy Required
Somerville does not require owner occupancy for ADUs, a right guaranteed by the Affordable Homes Act. This means you can rent both your main home and the ADU, making it a viable pure investment property. You're also free to live in the ADU and rent the main house.
Historic District Considerations
Somerville has historically significant areas including City of Somerville- Historic Preservation Commission, Old Powder House, Pleasant Street Historic District, Prospect Hill Tower, Winchester Center Historic District. 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.
Somerville ADU Rules at a Glance
Max Size
900 sq ft
% of Home
50%
Max Height
25 ft
Max Stories
2
Front Setback
10 ft
Side Setback
3 ft
Rear Setback
3 ft
Parking
None required
Approval
BY RIGHT
Owner Occupancy
Not required
Rental Allowed
Yes
Short-Term Rental
Not allowed
Somerville Building Department
Frequently Asked Questions
Are ADUs allowed by right in Somerville, MA?
Yes. ADUs in Somerville 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 guaranteed by the Affordable Homes Act.
What types of ADUs can I build in Somerville?
Somerville allows detached, attached, conversion ADUs. With up to 900 sq ft allowed, a detached ADU gives you the most flexibility for a full living space.
Do I need to live on the property to build an ADU in Somerville?
No. Somerville does not require owner occupancy — this is a right guaranteed by the Affordable Homes Act. You can rent both your main home and the ADU, making this a pure investment property if you choose.
How big can I build an ADU in Somerville, MA?
In Somerville, you can build an ADU up to 900 square feet or 50% of your home's living area, whichever is larger. With 900 sq ft, you have enough room for a full 2-bedroom cottage with a kitchen, bathroom, and living area. This is guaranteed by the Affordable Homes Act.
Does Somerville have historic district rules for ADUs?
Yes. Somerville has historically significant areas including City of Somerville- Historic Preservation Commission, Old Powder House, Pleasant Street Historic District, Prospect Hill Tower, Winchester Center Historic District. 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 Somerville?
Yes, long-term rentals are allowed for ADUs in Somerville. However, short-term rentals (like Airbnb) are not currently allowed for ADUs. With a population of 81,360, Somerville has strong rental demand.
Check Your Address
See exactly what ADU rules apply to your specific property in Somerville.