Build an ADU in Carroll.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Carroll — by-right. A detached ADU can be up to 950 sf, and ADU setbacks match your lot's single-family setbacks.
5 districts
Each district's single-family setbacks — which your ADU follows. The primary residential district is highlighted.
Verified against the official Carroll zoning ordinance · source · 2026-07-07
- Front
- 30 ft
- Side
- 20 ft
- Rear
- 50 ft
- Max coverage
- —
- Min lot
- 43,560 sf (~1.00 ac)
Principal single-family residential district. Min lot 1 acre (43,560 sf); multi-family buildings require an additional 10,000 sf per 1,000 sf of livable space beyond the single-family minimum (403.2). Min frontage 150 ft along principal access.
- Front
- 30 ft
- Side
- 20 ft
- Rear
- 25 ft
- Max coverage
- —
- Min lot
- 43,560 sf (~1.00 ac)
Mixed residential/commercial district. Min lot 1 acre (43,560 sf) for a single-family or two-family dwelling; min frontage 100 ft (403.3). RESIDENTIAL-use setbacks (recorded here): front 30, side 20, rear 25 ft COMMERCIAL-use setbacks in this district differ and tier by…
- Front
- 30 ft
- Side
- 20 ft
- Rear
- 25 ft
- Max coverage
- —
- Min lot
- 43,560 sf (~1.00 ac)
Min lot 1 acre (43,560 sf); multi-family buildings require +10,000 sf per 1,000 sf livable space beyond the single-family minimum (403.4). Min frontage 100 ft RESIDENTIAL-use setbacks (recorded here): front 30, side 20, rear 25 ft Front setback is 40 ft for COMMERCIAL use.
- Front
- 100 ft
- Side
- 25 ft
- Rear
- 25 ft
- Max coverage
- —
- Min lot
- 174,240 sf (~4.00 ac)
Min lot 4 acres (174,240 sf); for each sf of industrial space there must be 2 sf of open space (403.5).
- Front
- 40 ft
- Side
- 30 ft
- Rear
- 50 ft
- Max coverage
- —
- Min lot
- 87,120 sf (~2.00 ac)
Min lot 2 acres (87,120 sf) recorded here as the conservative default; reduced to 1 acre (43,560 sf) for single-family dwellings only WHERE MUNICIPAL WATER IS AVAILABLE, in which case RES 1 setbacks apply (403.6).
Form-based and downtown districts may use build-to lines instead of fixed setbacks (shown as “—”); verify your parcel's district before you build.
Carroll 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 Carroll (Coös County). A detached ADU can be up to 950 sf.
In Carroll's RES 1 zone, ADUs follow the single-family setbacks: 30 ft front, 20 ft side, and 50 ft rear. Carroll has 5 zoning districts in total — see the full table below. Confirm your exact zone with the town.