ADU rules in Cambridge, MA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Cambridge allows accessory dwelling units by right under the 2024 MA Affordable Homes Act and MGL c.40A s.3A, the statewide ADU mandate. Most residential districts now permit one ADU by right.
The Massachusetts Affordable Homes Act, signed in August 2024, amended MGL c.40A s.3A to require that every municipality in the state allow at least one accessory dwelling unit by right on every lot where a single-family home is allowed, up to 900 square feet or half the size of the primary unit. Cambridge has implemented this through updates to its zoning ordinance, and because Cambridge already permitted many forms of accessory units in two-family and multi-family districts, ADU approvals are broadly available throughout the city. Owner-occupancy cannot be required under the state law, and short-term rental of an ADU is restricted by the Cambridge STR registration rules. Permits go through the Cambridge Inspectional Services Department and design review under the zoning ordinance. Historic district properties face additional review from the Cambridge Historical Commission.
Contact your local code enforcement office for specific penalty information.
Cambridge, MA
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Side-by-side rule comparisons with other cities in Middlesex County.
See how other cities in Middlesex County handle adu rules.
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