ADU Regulations:
Cambridge
Regulations Snapshot
Rear and Side setbacks: 5 feet
Building Separation: no specified
Height: 4 stories
Separate utilities required: No
Stormwater management required: Drywell required if there is space
Specialized Stretch Energy Code: Yes
Impact Fees: $250 + $50/fixture for sewer
Building Constraints
Number of ADU’s allowed on a single family lot
As of February 10, 2025 Cambridge adopted two zoning petitions to allow multifamily housing citywide. For the first time in Cambridge zoning history, all residential neighborhoods have the same zoning rules and all districts (except open space) are zoned to allow multifamily housing.
Maximum square footage of an ADU (detached or attached)
Not restricted
Maximum Height
4 stories
Maximum lot coverage
The restriction here is “minimum open space” listed at 30%. This means that 30% of the lot must not be covered by a building structure. Decks, patios, walkways, green space and driveway for 1 space/unit all count toward the open space requirement.
Exterior appearance requirements
Compatible with the neighborhood’s existing buildings
Setbacks
Rear setback
5 feet
Side setback
5 feet
Front setback
10 feet
Distance between buildings
not specified
Height
The new petitions allow up to 4 stories or 45 feet
Parking
Parking requirement for an ADU
The new petition has eliminated parking requirements. The homeowner has the choice whether to add additional parking.
Specific parking requirements (location)
None
Where can the parking be located : Parking requirement for primary dwelling
None
Additional Requirements
Separate utilities required
No, connection to main house is allowed
Stormwater management required
Reviewed on a case by case basis. Generally if there is space to retain 1” of water from the roof of the ADU to a drywell it will be required
Site plan review required
No
Town impact fees
$250 + $50/fixture for sewer
Soils report required
Yes
Civil plans required
Yes
Short term rental allowed
Yes
Possible overlay districts
Historical and Floor Plain Overlays could require addition approvals
ADUs on multifamily lots
Allowed as long as other zoning requirements are met