Build an ADU in Marlborough.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Marlborough — 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 Marlborough zoning ordinance · source · 2026-07-07
- Front
- 40 ft
- Side
- 20 ft
- Rear
- 40 ft
- Max coverage
- —
- Min lot
- 65,340 sf (~1.50 ac)
Town's principal/general residential district (Sec 3 lists it simply as 'Residential'). Minimum lot area for an individual residence = 1.5 acres (65,340 sq ft), the same with or without town sewer, exclusive of wetlands and slopes over 15% (Sec 7.1 note 4).
- Front
- 25 ft
- Side
- 20 ft
- Rear
- 15 ft
- Max coverage
- —
- Min lot
- 10,000 sf (~0.23 ac)
Compact village-core residential district. Min lot area 10,000 sq ft both with and without town sewer, exclusive of wetlands and slopes over 15% (Sec 7.1 note 4). Frontage 100 ft Front setback measured from edge of approved right-of-way.
- Front
- 40 ft
- Side
- 25 ft
- Rear
- 40 ft
- Max coverage
- —
- Min lot
- 217,800 sf (~5.00 ac)
Rural district. Minimum lot area for an individual residence = 5 acres (217,800 sq ft), exclusive of wetlands and slopes over 15% (Sec 7.1 note 5; existing lots of record before 3/31/2001 grandfathered).
- Front
- 40 ft
- Side
- 25 ft
- Rear
- 40 ft
- Max coverage
- —
- Min lot
- 217,800 sf (~5.00 ac)
Scenic Rural district (lowest density). Minimum lot area for an individual residence = 5 acres (217,800 sq ft), exclusive of wetlands and slopes over 15% (Sec 7.1 note 5). Frontage 300 ft Front setback 40 ft from edge of approved right-of-way; gateway-corridor 60 ft rule…
- Front
- 15 ft
- Side
- 15 ft
- Rear
- 15 ft
- Max coverage
- —
- Min lot
- 10,000 sf (~0.23 ac)
Village-core commercial district. Frontage 100 ft Setbacks: 15 ft front (from edge of approved ROW), 15 ft side, 15 ft rear. No lot-coverage percentage; special exception required where contiguous structures+parking exceed 10,000 sq ft (note 8).
- Front
- 50 ft
- Side
- 35 ft
- Rear
- 35 ft
- Max coverage
- —
- Min lot
- 87,120 sf (~2.00 ac)
Route 124 commercial district. Min lot area 2 acres (87,120 sq ft), same with or without town sewer, exclusive of wetlands and slopes over 15% (Sec 7.1 note 4). Frontage 200 ft Setbacks: 50 ft front (from edge of approved ROW), 35 ft side, 35 ft rear; gateway-corridor 60 ft…
- Front
- 20 ft
- Side
- 20 ft
- Rear
- 20 ft
- Max coverage
- —
- Min lot
- 43,560 sf (~1.00 ac)
Route 101 commercial district; extends 500 ft back from the edge of the Rte 101 right-of-way (Sec 7.1 note 3). Min lot area 1 acre (43,560 sq ft), same with or without town sewer, exclusive of wetlands and slopes over 15% (Sec 7.1 note 4).
- Front
- 40 ft
- Side
- 20 ft
- Rear
- 20 ft
- Max coverage
- —
- Min lot
- 87,120 sf (~2.00 ac)
Route 12 commercial district. Min lot area 2 acres (87,120 sq ft) without town sewer, exclusive of wetlands and slopes over 15% (Sec 7.1 note 4; the 'with town sewer' cell is 'Not Applicable' for C4). Frontage 200 ft Setbacks: 40 ft front (from edge of approved ROW), 20 ft…
Form-based and downtown districts may use build-to lines instead of fixed setbacks (shown as “—”); verify your parcel's district before you build.
Marlborough 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 Marlborough (Cheshire County). A detached ADU can be up to 950 sf.
In Marlborough's R2 zone, ADUs follow the single-family setbacks: 40 ft front, 20 ft side, and 40 ft rear. Marlborough has 8 zoning districts in total — see the full table below. Confirm your exact zone with the town.