Build an ADU in Amherst.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Amherst — by-right. A detached ADU can be up to 950 sf, and ADU setbacks match your lot's single-family setbacks.
7 districts
Each district's single-family setbacks — which your ADU follows. The primary residential district is highlighted.
Verified against the official Amherst zoning ordinance · source · 2026-07-06
- Front
- 50 ft
- Side
- 25 ft
- Rear
- 25 ft
- Max coverage
- —
- Min lot
- 87,120 sf (~2.00 ac)
PRIMARY single-family residential district (Sec 4.3). Minimum lot area 2 acres = 87,120 sf, and that minimum area must contain NO wetland, NO flood plain, and NO slopes greater than 20% (4.3.C.1). Minimum frontage 200 ft (4.3.C.2).
- Front
- 50 ft
- Side
- 40 ft
- Rear
- 40 ft
- Max coverage
- —
- Min lot
- 152,460 sf (~3.50 ac)
Low-density transitional residential district forming the entry to the Northern Rural Zone (Sec 4.4; listed as 'NTR' in the Sec 2.1 code table). Minimum lot area 3.5 acres = 152,460 sf, which must contain NO wetland, NO flood plain, and NO slopes greater than 20% (4.4.C.1).
- Front
- 50 ft
- Side
- 40 ft
- Rear
- 40 ft
- Max coverage
- —
- Min lot
- 217,800 sf (~5.00 ac)
Lowest-density rural residential district protecting poor soils, steep slopes and limited-access land (Sec 4.5). Minimum lot area 5 acres = 217,800 sf, which must contain NO wetland, NO flood plain, and NO slopes greater than 20% (4.5.D.1).
- Front
- 50 ft
- Side
- 30 ft
- Rear
- 30 ft
- Max coverage
- —
- Min lot
- 43,560 sf (~1.00 ac)
Office district permitting professional/general offices, mixed office-residential use, and (per 3-10-26 amendment) multi-family residential development subject to site plan review (Sec 4.6). Minimum lot area 1 acre = 43,560 sf, EXCEPT a residential use requires 2 acres =…
- Front
- 50 ft
- Side
- 30 ft
- Rear
- 30 ft
- Max coverage
- —
- Min lot
- 43,560 sf (~1.00 ac)
General commercial district serving major commercial/business needs (Sec 4.7). Minimum lot area 1 acre = 43,560 sf (4.7.C.1). Minimum frontage 200 ft on a publicly maintained road, or 35 ft if approved/recorded as a reduced-frontage lot (4.7.C.2).
- Front
- 50 ft
- Side
- 30 ft
- Rear
- 30 ft
- Max coverage
- —
- Min lot
- 43,560 sf (~1.00 ac)
Limited commercial district serving neighborhood-scale commercial needs (Sec 4.8): small retail, offices, service stations, etc. Minimum lot area 1 acre = 43,560 sf (4.8.C.1). Minimum frontage 200 ft on a publicly maintained road, or 35 ft if approved/recorded as a…
- Front
- 50 ft
- Side
- 30 ft
- Rear
- 30 ft
- Max coverage
- —
- Min lot
- 43,560 sf (~1.00 ac)
Industrial district: light manufacturing, assembly, warehousing, laboratories, offices, limited retail, etc. Minimum lot area 1 acre = 43,560 sf (4.9.D.1). Minimum frontage 200 ft (4.9.D.2). Front setback per 4.9.E.1: new structure set back EITHER 50 ft OR 100 ft from the…
Form-based and downtown districts may use build-to lines instead of fixed setbacks (shown as “—”); verify your parcel's district before you build.
Amherst 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 Amherst (Hillsborough County). A detached ADU can be up to 950 sf.
In Amherst's RR zone, ADUs follow the single-family setbacks: 50 ft front, 25 ft side, and 25 ft rear. Amherst has 7 zoning districts in total — see the full table below. Confirm your exact zone with the town.