ADU Regulations:
Dedham
Regulations Snapshot
Rear and Side setbacks: 5 feet
Building Separation: 5 feet
Height: 2 stories
Separate utilities required: Sewer – yes, others – no
Stormwater management: No
Specialized Stretch Energy Code: Yes
Impact Fees: Water/sewer connection
Building Constraints
Number of ADU’s allowed on a single family lot
One ADU allowed per single-family lot, whether interior, detached, or attached
Maximum square footage of an ADU (detached or attached)
Up to 900 square feet or half the gross floor area of the primary dwelling, whichever is smaller
Maximum Height
2 stories
Maximum lot coverage
Same as regular zoning requirements
Exterior appearance requirements
Similar to primary dwelling
Setbacks
Rear setback
If the height of the ADU is less than 15 feet, rear setbacks are 5 feet. If over 15 feet, then 20 feet
Side setback
If the height of the ADU is less than 15 feet, side setbacks are 5 feet.. If over 15 feet, the 10 feet
Front setback
25 feet
Distance between buildings
10 feet
Parking
Parking requirement for an ADU
One parking spot is required unless within a half mile of a transit station
Where can the parking be located : Parking requirement for primary dwelling
2 parking spaces normally required for the primary dwelling
Additional Requirements
Separate utilities required
Water can tie to the main dwelling. Sewer has to go to street if possible. If sewer is tied into the house, the pipe to the street must be upgraded to pvc. The city engineering department will review to see if street lateral is available to tie into. Electric can come off the main house or or have it’s own service.
Stormwater management required
No storm water requirements unless doing large driveway
Town impact fees
No town fees, possible for Dedham/Westwood town water/sewer
Fire safety requirements
2 means of egress, bedroom egress window, hardwired smoke detector
Soils report required
Depending on location, will most likely only inspect the foundation hole after excavation. If abutting wetland then may require a report.
Civil plans required
Yes, showing utility hookups
Short term rental allowed
No
Possible overlay districts
Being in a historic, flood or wetland zone could trigger additional permitting for an ADU
ADUs on multifamily lots
Only allowed by right on single family lots