ADU Types Explained in Cambridge, MA
Learn about detached, attached, and conversion ADUs in Cambridge, Massachusetts. Compare costs, timelines, and which type is right for your property.
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.
ADU Types Available in Cambridge
Cambridge allows 3 type(s) of ADU. Each has different cost, timeline, and design implications.
- Detached ADU — a standalone building in your yard with its own entrance, utilities, and foundation. Best for privacy and rental income.
- Attached ADU — an addition connected to your main home that shares at least one wall. Lower construction costs than detached.
- Conversion ADU — transforms existing space like a basement, attic, or garage into a separate dwelling. Fastest and cheapest to build.
Which ADU Type Is Right for You?
The best ADU type for your property in Cambridge depends on your lot size, budget, and goals. If you want maximum rental income and privacy, a detached ADU is ideal. If budget is your priority, a conversion ADU reuses existing space and avoids foundation costs. An attached ADU offers a middle ground — lower cost than detached with a separate entrance. With 900 sq ft allowed, you have room for a comfortable 1-2 bedroom unit.
Learn More About ADU Rules in Cambridge
For full zoning details, see our ADU zoning guide for Cambridge. To understand what you'll spend, visit our ADU costs page for Cambridge.
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
What are the different types of ADUs I can build in Cambridge?
Cambridge allows detached, attached, conversion ADUs. Detached ADUs are standalone structures in your yard. Attached ADUs share a wall with your main home. Conversion ADUs transform existing space like a basement, attic, or garage. Each type has different costs, timelines, and design implications.
Which ADU type is cheapest to build in Cambridge?
Conversion ADUs are the most affordable option in Cambridge at $100-$200/sq ft, since you reuse existing structure and avoid foundation costs. See our ADU costs page for Cambridge for a full breakdown.
Can I build a detached ADU in my backyard in Cambridge?
Yes, detached ADUs are allowed in Cambridge. Your ADU must meet setback requirements — typically 5 ft from the rear property line. Check our ADU zoning page for Cambridge for exact setback distances.
Can I convert my garage into an ADU in Cambridge?
Yes, garage conversions are allowed in Cambridge. Converting an existing garage is one of the fastest and most affordable ways to add an ADU — you're reusing the existing structure and foundation.
Where can I find all ADU regulations for Cambridge?
Visit our complete ADU rules page for Cambridge, MA for a full overview of zoning, permits, size limits, setbacks, parking, and costs. We cover all Massachusetts municipalities with data sourced from local ordinances and state law.
Check Your Address
See exactly what ADU rules apply to your specific property in Cambridge.