Build an ADU in Washington.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Washington — by-right. A detached ADU can be up to 950 sf, and ADU setbacks match your lot's single-family setbacks.
- Front setback
- 30 ft
- Side setback
- 30 ft
- Rear setback
- 40 ft
- Max lot coverage
- 10%
- Min lot size
- 174,240 sf (~4.00 ac)
- Max detached ADU
- 950 sf
Figures reflect Washington's Town-wide residential zone and are a planning aid — your parcel's exact zone and overlays (wetland, shoreland) are verified before we lock your price.
Verified against the official Washington zoning ordinance · source · 2026-07-07
Washington 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 Washington (Sullivan County). A detached ADU can be up to 950 sf.
In Washington's Town-wide zone, ADUs follow the single-family setbacks: 30 ft front, 30 ft side, and 40 ft rear. Confirm your exact zone with the town.