Cambridge, MA
Cambridge, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 10/10
Last updated: 6.21.2024
Image source: USNews
What You Need To Know
ADUs are allowed in Cambridge in all zoning districts in structures in existence as of February 1st 2019. A single-family, two-family, or accessory structure may be altered to provide an ADU.
Type of ADU Permit Required
ADUs in Cambridge require a special permit.
ADU Rules in Cambridge
ADUs are only permitted in structures that have been in existence since on or before February, 1, 2019.
The principal residence must have at least 1,800 square feet of gross floor area.
The ADU is limited to 900 square feet or 35% of the gross floor area of the primary residence, whichever is less.
Only one ADU is permitted on any given lot.
A two-family home may be converted to a single family home with an ADU by right - no need for a special permit.
An ADU within or attached to an accessory structure cannot be greater than 900 square feet
The authority granting the special permit must determine that the appearance is compatible with the primary residence as well as the homes in the surrounding area.
For both ADUs within or attached to a principal residence and accessory structure
Special Permit Information
ADUs are not included in lot area per dwelling calculations.
The Board of Zoning Appeal may relax space requirements for ADUs built within structures; however, any gross floor area added must comply with ADU requirements.
To ensure a safe environment, setbacks and height restrictions may be altered.
EX: safe egress
Resources:
Cambridge Massachusetts Land Use Regulations- Article 4.20