ADU Regulations:
Watertown
Regulations Snapshot
Rear and Side setbacks: 5 feet
Building Separation: 10 feet
Height: 18 feet (1.5 stories)
Stormwater management: Required based on size of new building
Sprinkler system: Not needed
Separate utilities required: No
Impact Fees: Only $800 for site plan review
Building Constraints
Number of ADU’s allowed on a single family lot
One
Maximum square footage of an ADU (detached or attached)
The maximum floor area of an ADU shall not exceed 900-square feet, or 50% of the total gross floor area of the principal dwelling unit, whichever is smaller.
Maximum Height
18 feet (1.5 stories)
Maximum lot coverage
25%
Exterior appearance requirements
None
Setbacks
Rear setback
5 feet
Side setback
5 feet
Front setback
Level with or behind primary house
Distance between buildings
10 feet
Parking
Parking requirement for an ADU
Additional parking for the ADU not required
Where can the parking be located : Parking requirement for primary dwelling
Typically two off-street parking spaces
Additional Requirements
Separate utilities required
No
Stormwater management required
Sprinkler system required
Not required
Site plan review required
Yes required as a formality with the zoning department. Takes about 2 months and costs $800
Town impact fees
Only $800 for site plan review. If running new water/sewer connection to streets fees are: water $422 and sewer $375
Soils report required
No, the building department will inspect the hole prior to construction of the foundation
Civil Engineering plans required for utility hookups
Yes for stormwater calculations
Short term rental allowed
No
ADUs on multifamily lots
Allowed
Possible overlay districts
Floodplain and Historic Districts could affect an ADU build in Watertown