ADU Rules in Cambridge, Massachusetts

Cambridge is a Middlesex County city of about 120,000 directly across the Charles River from Boston. Home to Harvard University and the Massachusetts Institute of Technology (MIT), Cambridge is one of the world's premier centers of education and research. Cambridge is not part of Boston — it is an entirely separate city with its own progressive zoning policies. Cambridge has been a leader in allowing ADUs and Massachusetts enacted a statewide ADU law (Chapter 150, Acts of 2024) further expanding ADU rights.

Cambridge vs. Boston

• Cambridge: Middlesex County, north of the Charles River — use Cambridge's permit process
• Boston: Suffolk County, south of the Charles River — separate city, separate zoning code
• The two cities are connected by bridges but have completely separate governments

Cambridge Zoning Ordinance

The City of Cambridge Zoning Ordinance governs all land use in Cambridge. Cambridge has been a progressive leader on ADU policy, allowing ADUs in multiple residential zones to address the city's severe housing shortage.

Massachusetts Statewide ADU Law (2024)

Massachusetts Chapter 150, Acts of 2024 requires municipalities to allow ADUs by right in single-family zones. Verify how Cambridge has implemented this law alongside its existing ADU policies.

Permitted ADU Types

Per Cambridge Zoning Ordinance and state ADU law (verify current standards):

• Basement and interior conversions: Very common in Cambridge's dense rowhouse and multi-family stock
• Attached ADUs: With separate entrance
• Detached ADUs: In eligible zones (Cambridge is very dense — rear yard space is limited)
• Carriage house/garage conversions: Where structures exist

Size Limits

Per Massachusetts ADU law and Cambridge zoning:

• ADU cannot exceed smaller of: primary dwelling or 900 square feet (state law)
• Cambridge zoning may have additional or different standards — verify

Setbacks

Per Cambridge residential zone:

• Rear: Minimum setback
• Side: Minimum setback

Charles River Flood Zones and Wetlands

Parts of Cambridge near the Charles River may be in FEMA flood zones. Massachusetts Wetlands Protection Act applies within 100 feet of wetlands and 200 feet of rivers.

Historic Districts

Cambridge has local historic districts:

• Mid-Cambridge Historic District
• Old Cambridge Historic District (Harvard Square area)
• Cambridgeport Historic District and others

Properties in historic districts require review by the Cambridge Historical Commission.

MBTA Communities

Cambridge is a core MBTA community (Red Line, Green Line extension). The MBTA Communities law applies to Cambridge.

Permit Process

1. Verify zoning and state ADU law compliance: Cambridge Community Development Department
2. Historic Commission review: If in a local historic district
3. Conservation Commission review: If near the Charles River or wetlands
4. Submit plans: Cambridge Inspectional Services
5. Building permit and inspections
6. CO: Required before occupancy

Contact

Cambridge Community Development Department 344 Broadway, Cambridge, MA 02139 Phone: (617) 349-4600 Website: cambridgema.gov/zoninganddevelopment

Disclaimer: Massachusetts statewide ADU law (2024) applies. Cambridge has its own progressive ADU policies. Historic districts require additional review. Verify current standards before starting any project.