Build an ADU in Hillsborough.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Hillsborough — 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 Hillsborough zoning ordinance · source · 2026-07-07
- Front
- 30 ft
- Side
- 15 ft
- Rear
- 20 ft
- Max coverage
- 25% building
- Min lot
- 40,000 sf (~0.92 ac)
Principal single-family residential district; single-family dwellings permitted by right (Table 4). Setbacks (dwellings): front 30 / side 15 / rear 20, measured from the edge of the public or private ROW (229-21).
- Front
- 30 ft
- Side
- 25 ft
- Rear
- 50 ft
- Max coverage
- 25% building
- Min lot
- 87,120 sf (~2.00 ac)
Covers most of the town's land area; single-family dwellings permitted by right (Table 4). Setbacks (dwellings): front 30 / side 25 / rear 50 from edge of ROW. Min lot 2 acres (87,120 sf) + 200 ft frontage for a single-dwelling unit (Table 1) — flat, NOT utility-tiered.
- Front
- 30 ft
- Side
- 15 ft
- Rear
- 20 ft
- Max coverage
- 25% building
- Min lot
- 40,000 sf (~0.92 ac)
Purpose: preserve historic residential character of Upper Village and Bridge Village while encouraging infill (229-19.1.A). Same dimensional standards as the Residential District: dwellings 30/15/20 setbacks from ROW edge, 25% building coverage, height 50 ft Min lot tiered…
- Front
- 30 ft
- Side
- 15 ft
- Rear
- 20 ft
- Max coverage
- 25% building
- Min lot
- 40,000 sf (~0.92 ac)
Single-family permitted by right. Same dimensional standards as the Residential District: dwellings 30/15/20 setbacks from ROW edge, 25% building coverage, height 50 ft Min lot tiered (Table 2 single-dwelling): 10,000 sf w+s / 20,000 sf water or sewer / 40,000 sf no utilities…
- Front
- 30 ft
- Side
- 15 ft
- Rear
- 20 ft
- Max coverage
- 25% building
- Min lot
- 40,000 sf (~0.92 ac)
Added TM 2015 for the Emerald Lake Village area; single-family permitted by right. Dwellings 30/15/20 setbacks from ROW edge, 25% building coverage, height 50 ft Min lot tiered (Table 2 single-dwelling): 10,000 sf w+s / 20,000 sf water or sewer / 40,000 sf no utilities…
- Front
- 50 ft
- Side
- 25 ft
- Rear
- 50 ft
- Max coverage
- 25% building
- Min lot
- 87,120 sf (~2.00 ac)
Hillsborough Centre area, established under RSA 674:43-44 with a Historic District Commission (229-19.4); single-family permitted by right but exterior changes are subject to Commission review. Table 3 has a district-specific 'Historic District - All Uses' row: 50/25/50…
- Front
- 30 ft
- Side
- 15 ft
- Rear
- 20 ft
- Max coverage
- 25% building
- Min lot
- 40,000 sf (~0.92 ac)
Values recorded are Table 3's DWELLINGS row for this district group (30/15/20, 25% building coverage) with Table 2's single-dwelling no-utilities lot minimum (40,000 sf, 125 ft frontage; 10,000/20,000 sf with municipal utilities).
- Front
- 0 ft
- Side
- 0 ft
- Rear
- 10 ft
- Max coverage
- 75% building
- Min lot
- 5,000 sf (~0.11 ac)
Downtown district. All uses: front setback min 0 with a MAXIMUM front setback of 25 ft (build-to); side 0 only 'if adequate fire protection can be provided for primary building' (Table 3 note 3); rear 10 ft Coverage 75% building footprint.
Form-based and downtown districts may use build-to lines instead of fixed setbacks (shown as “—”); verify your parcel's district before you build.
Hillsborough 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 Hillsborough (Hillsborough County). A detached ADU can be up to 950 sf.
In Hillsborough's Residential zone, ADUs follow the single-family setbacks: 30 ft front, 15 ft side, and 20 ft rear. Hillsborough has 8 zoning districts in total — see the full table below. Confirm your exact zone with the town.