ADU Zoning in Cambridge, MA
Complete ADU zoning guide for Cambridge, Massachusetts. Learn about allowed ADU types, approval process, size limits, and local zoning regulations.
ADU Regulations in Cambridge
Cambridge 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. Cambridge may also have additional local regulations that supplement the state baseline.
By-Right Approval: No Hearing Required
ADUs in Cambridge 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
Cambridge 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
Cambridge 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
Cambridge has historically significant areas including Cambridge Historical Comm, East Cambridge Historic District, Garfield Street 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.
Conservation and Wetlands
Cambridge has conservation areas including Rock Meadow Conservation Area, Shade's Mills Conservation Area. If your property is near a wetland, river, or conservation area, you may need approval from the Conservation Commission before building an ADU. Massachusetts requires a buffer zone (typically 100 feet) around wetlands, and construction within this area requires a Notice of Intent filing.
Cambridge 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
5 ft
Rear Setback
5 ft
Parking
None required
Approval
BY RIGHT
Owner Occupancy
Not required
Rental Allowed
Yes
Short-Term Rental
Not allowed
Cambridge Building Department
Cambridge Inspectional Services
831 Massachusetts Ave # 1, Cambridge, MA 02139, USA
Phone: (617) 349-6100
Frequently Asked Questions
Are ADUs allowed by right in Cambridge, MA?
Yes. ADUs in Cambridge 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 Cambridge?
Cambridge 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 Cambridge?
No. Cambridge 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 Cambridge, MA?
In Cambridge, 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 Cambridge have historic district rules for ADUs?
Yes. Cambridge has historically significant areas including Cambridge Historical Comm, East Cambridge Historic District, Garfield Street 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 Cambridge?
Yes, long-term rentals are allowed for ADUs in Cambridge. However, short-term rentals (like Airbnb) are not currently allowed for ADUs. With a population of 118,403, Cambridge has strong rental demand.
Check Your Address
See exactly what ADU rules apply to your specific property in Cambridge.