Build an ADU in Northumberland.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Northumberland — 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 Northumberland zoning ordinance · source · 2026-07-07
- Front
- 75 ft
- Side
- 20 ft
- Rear
- 20 ft
- Max coverage
- 50% lot
- Min lot
- 43,560 sf (~1.00 ac)
PRIMARY single-family residential district: purpose is 'to create a residential neighborhood adjacent to the more dense and mixed use areas of Groveton and Northumberland Villages.' Permitted uses: single and two-family dwellings, home occupations, agriculture, single…
- Front
- 50 ft
- Side
- 10 ft
- Rear
- 15 ft
- Max coverage
- —
- Min lot
- 10,000 sf (~0.23 ac)
One of two Village Residential districts covering the built cores of Groveton Village, Northumberland Village and Dean Brook Park, mostly served by public water and sewer. Min lot 10,000 sf WHERE SERVED BY PUBLIC WATER AND SEWER; where either service is unavailable, min lot…
- Front
- 50 ft
- Side
- 10 ft
- Rear
- 15 ft
- Max coverage
- —
- Min lot
- 20,000 sf (~0.46 ac)
Second Village Residential district (moderate density). Min lot 20,000 sf WHERE SERVED BY WATER AND SEWER; where either service is unavailable, min lot must be adequate for state septic approval (Area Req.
- Front
- 75 ft
- Side
- 30 ft
- Rear
- 30 ft
- Max coverage
- 50% lot
- Min lot
- 87,120 sf (~2.00 ac)
Preserves the town's best agricultural lands (Connecticut River flood plain and Lost Nation Road hill farms). Min lot 2 acres (87,120 sf). Min frontage 200 ft Front yard 75 ft from the CENTERLINE of the road (or no less than abutting dwellings); side 30 ft; rear 30 ft (Sec…
- Front
- 75 ft
- Side
- 40 ft
- Rear
- 40 ft
- Max coverage
- —
- Min lot
- —
Heavy industry (may require pollution monitoring).
- Front
- 75 ft
- Side
- 40 ft
- Rear
- 40 ft
- Max coverage
- 50% lot
- Min lot
- —
Light industry that creates no smoke, odor, sound or other off-site hazards.
- Front
- 25 ft
- Side
- —
- Rear
- —
- Max coverage
- —
- Min lot
- —
Concentrates commercial activity in Groveton and Northumberland Village. Min frontage 100 ft Front yard 25 ft measured FROM THE CURB (or no less than abutting properties) -- the ordinance's only Commercial-District yard standard; no side or rear yard dimension is specified…
- Front
- 75 ft
- Side
- 20 ft
- Rear
- 20 ft
- Max coverage
- —
- Min lot
- 43,560 sf (~1.00 ac)
Forestry district where soils/terrain are often unsuitable for development. Permitted uses in addition to timber management include single-family dwellings, camps, agricultural management, land-management roads, primitive recreation, mineral extraction under 5 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.
Northumberland 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 Northumberland (Coös County). A detached ADU can be up to 950 sf.
In Northumberland's Residential Low Density zone, ADUs follow the single-family setbacks: 75 ft front, 20 ft side, and 20 ft rear. Northumberland has 8 zoning districts in total — see the full table below. Confirm your exact zone with the town.