Build an ADU in Allenstown.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Allenstown — by-right. A detached ADU can be up to 950 sf, and ADU setbacks match your lot's single-family setbacks.
13 districts
Each district's single-family setbacks — which your ADU follows. The primary residential district is highlighted.
Verified against the official Allenstown zoning ordinance · source · 2026-07-06
- Front
- 20 ft
- Side
- 15 ft
- Rear
- 30 ft
- Max coverage
- 40% building
- Min lot
- 10,000 sf (~0.23 ac)
Front measured from any street; rear 30, side 15 (Sec.703.2). R1 = land served by both Town water AND Town sewer; min lot 10,000 sf with 100 ft frontage (Sec.703.4). 2-family/multifamily need 10,000 sf of lot per dwelling unit where water+sewer available (Sec.703.7).
- Front
- 20 ft
- Side
- 15 ft
- Rear
- 30 ft
- Max coverage
- 40% building
- Min lot
- 40,000 sf (~0.92 ac)
Same setbacks/coverage/height as R1 (unified Sec.703). R2 = land served by neither Town water nor sewer; when town water OR sanitary sewers are not available, min lot 40,000 sf with 200 ft frontage (Sec.703.5).
- Front
- 20 ft
- Side
- 15 ft
- Rear
- 30 ft
- Max coverage
- 40% building
- Min lot
- 40,000 sf (~0.92 ac)
Same setbacks/coverage/height as R1. R3 = land served by Town water only. Because Sec.703.4's 10,000 sf tier requires BOTH water AND sewer, a water-only lot falls under Sec.703.5 (water OR sewer not available) = 40,000 sf / 200 ft frontage.
- Front
- 20 ft
- Side
- 15 ft
- Rear
- 30 ft
- Max coverage
- 40% building
- Min lot
- 40,000 sf (~0.92 ac)
Same setbacks/coverage/height as R1. R4 = land served by Town sewer only. Sewer-only lot lacks the water half of Sec.703.4's water-AND-sewer 10,000 sf tier, so it falls under Sec.703.5 = 40,000 sf / 200 ft frontage.
- Front
- 20 ft
- Side
- 30 ft
- Rear
- 30 ft
- Max coverage
- —
- Min lot
- 217,800 sf (~5.00 ac)
Front 20 ft from any street; side and rear each 30 ft (Sec.604). Single-family: min 5 acres (217,800 sf) with 200 ft frontage; two-family: min 10 acres with 200 ft frontage (Sec.601.1). Accessory garage may sit 10 ft from rear line; utility shed/greenhouse <=200 sf may sit 5…
- Front
- 20 ft
- Side
- 15 ft
- Rear
- 40 ft
- Max coverage
- 70% building
- Min lot
- —
Front 20 ft from front lot line, side 15 ft (unless approved fire wall), rear 40 ft (Sec.804). Min frontage 75 ft (Sec.804.6); no explicit minimum lot area stated (null).
- Front
- 20 ft
- Side
- 15 ft
- Rear
- 40 ft
- Max coverage
- 70% building
- Min lot
- —
Front 20 ft from front lot line, side 15 ft (unless approved fire wall), rear 40 ft (Sec.904). Min frontage 75 ft (Sec.904.7); no explicit minimum lot area stated (null).
- Front
- 20 ft
- Side
- 15 ft
- Rear
- 40 ft
- Max coverage
- 70% building
- Min lot
- —
Side 15 ft (unless approved fire wall) and rear 40 ft are stated in Sec.1004.2-3. Min frontage 75 ft (Sec.1004.6); no explicit minimum lot area stated (null).
- Front
- 10 ft
- Side
- —
- Rear
- 10 ft
- Max coverage
- —
- Min lot
- 5,000 sf (~0.11 ac)
Overlay district (Sec.2402). minLotSqft=5,000 reflects the residential tier.
- Front
- —
- Side
- —
- Rear
- —
- Max coverage
- —
- Min lot
- —
Overlay district (Sec.2301). No conventional front/side/rear/coverage/min-lot table; regulated by performance standards instead: non-agricultural buildings must sit at least 100 ft from agricultural operations, and residential subdivision on lots >15 acres with >=200 ft…
- Front
- —
- Side
- —
- Rear
- —
- Max coverage
- —
- Min lot
- —
Overlay district (Sec.2503) protecting aquifers; imposes use/performance restrictions (e.g., impervious/hazardous-material controls), not dimensional setbacks.
- Front
- —
- Side
- —
- Rear
- —
- Max coverage
- —
- Min lot
- —
Overlay district (Ch.20) delineating where Manufactured Housing Parks may be located (conditional use).
- Front
- —
- Side
- —
- Rear
- —
- Max coverage
- —
- Min lot
- —
Overlay district (Ch.28) implementing EPA MS4 stormwater/illicit-discharge requirements; performance/stormwater standards only, no dimensional setbacks.
Form-based and downtown districts may use build-to lines instead of fixed setbacks (shown as “—”); verify your parcel's district before you build.
Allenstown 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 Allenstown (Merrimack County). A detached ADU can be up to 950 sf.
In Allenstown's R1 zone, ADUs follow the single-family setbacks: 20 ft front, 15 ft side, and 30 ft rear. Allenstown has 13 zoning districts in total — see the full table below. Confirm your exact zone with the town.