Build an ADU in Merrimack.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Merrimack — by-right. A detached ADU can be up to 950 sf, and ADU setbacks match your lot's single-family setbacks.
9 districts
Each district's single-family setbacks — which your ADU follows. The primary residential district is highlighted.
Verified against the official Merrimack zoning ordinance · source · 2026-07-06
- Front
- 50 ft
- Side
- 30 ft
- Rear
- 60 ft
- Max coverage
- —
- Min lot
- 100,000 sf (~2.30 ac)
Single-family only (two-family and multi-family NOT permitted). Min lot 100,000 sf, frontage 250 ft, depth 300 ft Merrimack's residential district is soil-tiered: R-1 applies to severe-soils areas AND all mapped residential areas regardless of soils (Zoning Map incorporated…
- Front
- 50 ft
- Side
- 30 ft
- Rear
- 60 ft
- Max coverage
- —
- Min lot
- 80,000 sf (~1.84 ac)
Single-family only (two-family and multi-family NOT permitted). Min lot 80,000 sf, frontage 200 ft, depth 200 ft Applies where soils have moderate limitations for sanitary systems; contiguous non-wetland soil area required; excludes wetland/flood hazard soils.
- Front
- 30 ft
- Side
- 20 ft
- Rear
- 60 ft
- Max coverage
- —
- Min lot
- 40,000 sf (~0.92 ac)
Slight-soils tier. Single-family min lot 40,000 sf (frontage 150 ft, depth 150 ft; front 30/side 20/rear 60). Two-family requires 80,000 sf (frontage 200, depth 200; front 50/side 20/rear 60 per Note 2).
- Front
- 30 ft
- Side
- 20 ft
- Rear
- 60 ft
- Max coverage
- —
- Min lot
- 40,000 sf (~0.92 ac)
Public-water-and-sewer tier; overrides R-1/R-2/R-3 criteria where R-4 provisions are met (Note 4), except for the mapped portion of the R-1 District. Single-family min lot 40,000 sf (frontage 150, depth 150; front 30/side 20/rear 60).
- Front
- 30 ft
- Side
- 20 ft
- Rear
- 40 ft
- Max coverage
- —
- Min lot
- 20,000 sf (~0.46 ac)
C-1 and C-2 share one dimensional row (min lot 20,000 sf, frontage 125, depth 125; front 30/side 20/rear 40).
- Front
- 30 ft
- Side
- 20 ft
- Rear
- 40 ft
- Max coverage
- —
- Min lot
- 20,000 sf (~0.46 ac)
Distinct base district but shares the C-1/C-2 dimensional row (min lot 20,000 sf, frontage 125, depth 125; front 30/side 20/rear 40).
- Front
- 50 ft
- Side
- 20 ft
- Rear
- 30 ft
- Max coverage
- —
- Min lot
- —
No min lot area/frontage/depth stated for industrial buildings (blank in table).
- Front
- —
- Side
- —
- Rear
- —
- Max coverage
- —
- Min lot
- —
Table leaves all dimensional cells blank; governed by reference/context per Notes 5 & 9. All development must be served by public water and sewer; industrial access limited to Continental Boulevard extended (Note 5).
- Front
- 200 ft
- Side
- 200 ft
- Rear
- 200 ft
- Max coverage
- —
- Min lot
- 1,000,000 sf (~22.96 ac)
Min lot 1,000,000 sf, frontage 1,000 ft, depth 500 ft; all yard setbacks 200 ft Note 7: all setbacks to building lines/parking/site improvements (except landscaping and access ways) minimum 100 ft; minimum 200 ft from Camp Sargent Rd and Tallant Rd with a 100 ft landscaped…
Form-based and downtown districts may use build-to lines instead of fixed setbacks (shown as “—”); verify your parcel's district before you build.
Merrimack 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 Merrimack (Hillsborough County). A detached ADU can be up to 950 sf.
In Merrimack's R-1 zone, ADUs follow the single-family setbacks: 50 ft front, 30 ft side, and 60 ft rear. Merrimack has 9 zoning districts in total — see the full table below. Confirm your exact zone with the town.