Build an ADU in Portsmouth.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Portsmouth — by-right. A detached ADU can be up to 950 sf, and ADU setbacks match your lot's single-family setbacks.
15 districts
Each district's single-family setbacks — which your ADU follows. The primary residential district is highlighted.
Verified against the official Portsmouth zoning ordinance · source · 2026-07-05
- Front
- 30 ft
- Side
- 10 ft
- Rear
- 30 ft
- Max coverage
- 20% building
- Min lot
- 15,000 sf (~0.34 ac)
- Front
- 50 ft
- Side
- 20 ft
- Rear
- 40 ft
- Max coverage
- 5% building
- Min lot
- 217,800 sf (~5.00 ac)
5 acres.
- Front
- 30 ft
- Side
- 20 ft
- Rear
- 40 ft
- Max coverage
- 10% building
- Min lot
- 43,560 sf (~1.00 ac)
1 acre. Frontage 150.
- Front
- 15 ft
- Side
- 10 ft
- Rear
- 20 ft
- Max coverage
- 25% building
- Min lot
- 7,500 sf (~0.17 ac)
- Front
- 5 ft
- Side
- 10 ft
- Rear
- 25 ft
- Max coverage
- 30% building
- Min lot
- 5,000 sf (~0.11 ac)
- Front
- 5 ft
- Side
- 10 ft
- Rear
- 20 ft
- Max coverage
- 35% building
- Min lot
- 3,500 sf (~0.08 ac)
- Front
- 30 ft
- Side
- 25 ft
- Rear
- 25 ft
- Max coverage
- 20% building
- Min lot
- 217,800 sf (~5.00 ac)
5 acres; 10,000 sf per DU.
- Front
- 5 ft
- Side
- 10 ft
- Rear
- 15 ft
- Max coverage
- 40% building
- Min lot
- 7,500 sf (~0.17 ac)
- Front
- 5 ft
- Side
- 10 ft
- Rear
- 15 ft
- Max coverage
- 40% building
- Min lot
- 7,500 sf (~0.17 ac)
- Front
- 20 ft
- Side
- 15 ft
- Rear
- 15 ft
- Max coverage
- 35% building
- Min lot
- 20,000 sf (~0.46 ac)
- Front
- 30 ft
- Side
- 30 ft
- Rear
- 50 ft
- Max coverage
- 30% building
- Min lot
- 43,560 sf (~1.00 ac)
1 acre.
- Front
- 30 ft
- Side
- 30 ft
- Rear
- 20 ft
- Max coverage
- 30% building
- Min lot
- 20,000 sf (~0.46 ac)
- Front
- 70 ft
- Side
- 50 ft
- Rear
- 50 ft
- Max coverage
- 50% building
- Min lot
- 87,120 sf (~2.00 ac)
2 acres.
- Front
- 70 ft
- Side
- 50 ft
- Rear
- 50 ft
- Max coverage
- 50% building
- Min lot
- 87,120 sf (~2.00 ac)
2 acres.
- Front
- 50 ft
- Side
- 75 ft
- Rear
- 50 ft
- Max coverage
- 30% building
- Min lot
- 130,680 sf (~3.00 ac)
3 acres.
Form-based and downtown districts may use build-to lines instead of fixed setbacks (shown as “—”); verify your parcel's district before you build.
Portsmouth 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 Portsmouth (Rockingham County). A detached ADU can be up to 950 sf.
In Portsmouth's SRB zone, ADUs follow the single-family setbacks: 30 ft front, 10 ft side, and 30 ft rear. Portsmouth has 15 zoning districts in total — see the full table below. Confirm your exact zone with the town.