Build an ADU in Grantham.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Grantham — by-right. A detached ADU can be up to 950 sf, and ADU setbacks match your lot's single-family setbacks.
6 districts
Each district's single-family setbacks — which your ADU follows. The primary residential district is highlighted.
Verified against the official Grantham zoning ordinance · source · 2026-07-07
- Front
- 35 ft
- Side
- 10 ft
- Rear
- 10 ft
- Max coverage
- 20% building
- Min lot
- 43,560 sf (~1.00 ac)
Grantham's principal single-family residential district (1-acre minimum; the bulk of the town's residential land). Minimum lot area 1 acre = 43,560 sf, but NO water bodies, wetland soils, or any portion of slopes steeper than 20% may be counted toward the minimum, so…
- Front
- 75 ft
- Side
- 35 ft
- Rear
- 35 ft
- Max coverage
- 8% building
- Min lot
- 196,020 sf (~4.50 ac)
Lower-density rural residential district. Minimum lot area 4.5 acres = 196,020 sf, excluding water bodies, wetland soils, and slopes steeper than 20% (Art V-B, 3(a)). Frontage >=200 ft Setbacks measured from lot boundary / road right-of-way (not centerline): 75 ft frontage,…
- Front
- 75 ft
- Side
- 35 ft
- Rear
- 35 ft
- Max coverage
- 8% building
- Min lot
- 217,800 sf (~5.00 ac)
Most remote / lowest-density rural residential district. Minimum lot area 5 acres = 217,800 sf, excluding water bodies, wetland soils, and slopes steeper than 20% (Art V-C, 3(a)). Frontage >=300 ft (Art V-C, 3(c)).
- Front
- 25 ft
- Side
- 10 ft
- Rear
- 10 ft
- Max coverage
- 25% building
- Min lot
- 17,424 sf (~0.40 ac)
Historic village core, created to recognize that pre-1990 lots here are smaller than the surrounding rural-residential minimums. Minimum lot area 0.4 acre = 17,424 sf, excluding water bodies, wetland soils, and slopes steeper than 20% (Art V-D, 3(a)).
- Front
- 35 ft
- Side
- 10 ft
- Rear
- 10 ft
- Max coverage
- 50% lot
- Min lot
- 43,560 sf (~1.00 ac)
Mixed medium-density residential/business district. Minimum lot area 1 acre = 43,560 sf, excluding water bodies, wetland soils, and slopes steeper than 20% (Art IV-A, 3(a)). Coverage cap 50% and it is a LOT-coverage basis: building coverage 'including parking and driveway…
- Front
- 35 ft
- Side
- 10 ft
- Rear
- 10 ft
- Max coverage
- 50% lot
- Min lot
- 43,560 sf (~1.00 ac)
Mixed medium-density residential/business/light-industrial district. Minimum lot area 1 acre = 43,560 sf, excluding water bodies, wetland soils, and slopes steeper than 20% (Art IV-B, 3(a)). Frontage >=150 ft Setbacks measured from lot boundary / road right-of-way (not…
Form-based and downtown districts may use build-to lines instead of fixed setbacks (shown as “—”); verify your parcel's district before you build.
Grantham 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 Grantham (Sullivan County). A detached ADU can be up to 950 sf.
In Grantham's RR1 zone, ADUs follow the single-family setbacks: 35 ft front, 10 ft side, and 10 ft rear. Grantham has 6 zoning districts in total — see the full table below. Confirm your exact zone with the town.