Build an ADU in Seabrook.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Seabrook — by-right. A detached ADU can be up to 950 sf, and ADU setbacks match your lot's single-family setbacks.
8 districts
Each district's single-family setbacks — which your ADU follows. The primary residential district is highlighted.
Verified against the official Seabrook zoning ordinance · source · 2026-07-06
- Front
- 20 ft
- Side
- 10 ft
- Rear
- 10 ft
- Max coverage
- —
- Min lot
- 20,000 sf (~0.46 ac)
Rural district; single-family dwelling and single-family + ADU min lot 20,000 sf. Min % open space 25%. Lot must accommodate a 125'x125' square (frontage, depth, width all 125').
- Front
- 30 ft
- Side
- 15 ft
- Rear
- 15 ft
- Max coverage
- —
- Min lot
- 30,000 sf (~0.69 ac)
Commercial district; single-family dwelling and single-family + ADU permitted at 30,000 sf min lot. Min % open space 25%. Minimum 20' greenbelt along Lafayette Road. Lot must accommodate a 125'x125' square (frontage, depth, width all 125').
- Front
- 50 ft
- Side
- 15 ft
- Rear
- 15 ft
- Max coverage
- —
- Min lot
- 30,000 sf (~0.69 ac)
Industrial district; 0 residential buildings/dwelling units permitted per lot (non-residential building min lot 30,000 sf). Min % open space 25%. Lot must accommodate a 125'x125' square (frontage, depth, width all 125').
- Front
- —
- Side
- —
- Rear
- —
- Max coverage
- —
- Min lot
- —
Conservation district. All dimensional/setback/lot-area cells in the Section 7 table are blank ('--') and Minimum % of Open Space is 100% -- effectively no buildable development; standards are contextual/not established for this zone.
- Front
- 30 ft
- Side
- 15 ft
- Rear
- 15 ft
- Max coverage
- —
- Min lot
- 20,000 sf (~0.46 ac)
Harbor Commercial district; single-family dwelling and single-family + ADU min lot 20,000 sf. Min % open space 25%. Lot must accommodate a 100'x100' square (frontage, depth, width all 100').
- Front
- 20 ft
- Side
- 10 ft
- Rear
- 10 ft
- Max coverage
- —
- Min lot
- 15,000 sf (~0.34 ac)
Primary town-wide single-family residential district. Min % open space 25%. Lot must accommodate a 100'x100' square (frontage, depth and width all 100'). No max coverage %; density governed by open space and lot area.
- Front
- 20 ft
- Side
- 10 ft
- Rear
- 10 ft
- Max coverage
- —
- Min lot
- 15,000 sf (~0.34 ac)
Smithtown Village residential district (see also Section 4). Min % open space 25%. Lot must accommodate a 100'x100' square (frontage, depth, width all 100').
- Front
- 15 ft
- Side
- 15 ft
- Rear
- 15 ft
- Max coverage
- —
- Min lot
- 30,000 sf (~0.69 ac)
Smithtown Village / North Village mixed-use district (see Section 4). Min % open space 20% (lowest in town). Minimum 20' greenbelt along Lafayette Road. Lot must accommodate a 125'x125' square (frontage, depth, width all 125').
Form-based and downtown districts may use build-to lines instead of fixed setbacks (shown as “—”); verify your parcel's district before you build.
Seabrook ADU FAQ
Yes. Under NH RSA 674:71-73 (HB 577), one accessory dwelling unit is allowed by-right on single-family lots statewide, including Seabrook (Rockingham County). A detached ADU can be up to 950 sf.
In Seabrook's 1 zone, ADUs follow the single-family setbacks: 20 ft front, 10 ft side, and 10 ft rear. Seabrook has 8 zoning districts in total — see the full table below. Confirm your exact zone with the town.