Accessory Dwelling Units (ADUs) in Cambridge, MA
Cambridge has long been a leader in progressive housing policy, and Accessory Dwelling Units (ADUs) are no exception. With recent zoning reforms and the introduction of the state’s Affordable Homes Act, homeowners in Cambridge have more flexibility than ever when it comes to creating in-law suites, backyard cottages, and basement apartments.
Here’s what you need to know about building an ADU in Cambridge 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.
Key provisions include:
ADUs allowed by right without needing a special permit
Max size: 900 sq ft or 50% of the main dwelling’s floor area (whichever is smaller)
No owner-occupancy requirement — you don’t need to live on the property
No parking requirement for ADUs within 0.5 miles of public transit
These rules apply statewide and override any stricter local rules for qualifying “protected use” ADUs.
Cambridge’s Local ADU Policy
Cambridge was ahead of the curve in legalizing ADUs and allowing backyard cottages as part of broader zoning reforms dating back several years. ADUs are permitted in most residential zones, and the city’s zoning ordinance has been updated to reduce barriers such as minimum lot sizes and density limits.
That said, certain older requirements—like owner occupancy or more restrictive dimensional standards—may still appear in local code but are now overridden by state law if the ADU qualifies as a protected use.
For homeowners, this means it’s now easier to:
Convert basements and attics into separate units
Add detached cottages in backyards
Avoid the need for a zoning variance or special permit
Community Sentiment & Local Implementation
Cambridge has been at the forefront of zoning reform. In early 2025, the City Council voted 8–1 to eliminate single-family-only zoning entirely. The new rules allow:
Multifamily housing up to four stories by right citywide
Up to six stories on larger lots (5,000+ sq ft) if 20% of units are affordable
This landmark change underscores the city’s commitment to expanding housing options—and ADUs are a key part of that toolkit.
Public sentiment has been mixed but engaged:
Supporters emphasize the benefits of increased density, affordability, and transit-accessibility. One resident remarked, “Cheaper housing, plus higher density means more support for local businesses and expanded transit.”
Others voice concern over neighborhood character and infrastructure strain. “A 6-story building next to a single-family home feels like overreach. It’ll change the feel of the neighborhood,” said another.
Still, the city’s overall direction is clear: Cambridge is moving toward greater housing flexibility—and ADUs play a vital role in that transition.
What This Means for Homeowners in Cambridge
If you're considering an ADU in Cambridge, the combination of local zoning reform and state protections creates a favorable environment. You can likely proceed by right without needing special approval, provided your ADU:
Meets setback and size limits
Complies with building and safety codes
Falls under the “protected use” provisions of the Affordable Homes Act
Get a Custom ADU Roadmap for Your Property
We offer a comprehensive ADU Roadmap Report tailored to your Cambridge property. It includes:
On-site visit and feasibility analysis
Cost estimate and construction timeline
Local permitting guidance
Rental income projections
Referrals to experienced ADU contractors
👉 Schedule Your ADU Roadmap Consultation
Note: For the most accurate and current information on ADU regulations in Cambridge, we recommend checking with the city’s Community Development Department or working with a local expert.
