Build an ADU in Brentwood.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Brentwood — by-right. A detached ADU can be up to 950 sf, and ADU setbacks match your lot's single-family setbacks.
5 districts
Each district's single-family setbacks — which your ADU follows. The primary residential district is highlighted.
Verified against the official Brentwood zoning ordinance · source · 2026-07-06
- Front
- 75 ft
- Side
- 25 ft
- Rear
- 25 ft
- Max coverage
- —
- Min lot
- 87,120 sf (~2.00 ac)
PRIMARY single-family residential district; defined as all land not in the Commercial/Industrial or Professional Office districts (sec 300.001.004). FRONT setback of 75 ft is measured from the CENTERLINE of the abutting road (not the property line), exclusive of new Route 125…
- Front
- 125 ft
- Side
- 25 ft
- Rear
- —
- Max coverage
- —
- Min lot
- 120,000 sf (~2.75 ac)
FRONT setback varies by location: 125 ft from edge of pavement for lots fronting Routes 125 and 27; 75 ft from centerline of an internal subdivision/industrial-park road; 50 ft from edge of ROW on the Pine Road commercial/industrial portion (sec 300.002.001.005.A).
- Front
- 75 ft
- Side
- 40 ft
- Rear
- 40 ft
- Max coverage
- 40% building
- Min lot
- 130,680 sf (~3.00 ac)
One mapped district (sec 300.001.002) with two use-based standard sets. PROFESSIONAL OFFICE standards (shown here): min lot 3 acres (130,680 sf); building coverage within foundation lines not to exceed 40% of lot area; front yard 75 ft from road centerline; side and rear…
- Front
- 75 ft
- Side
- —
- Rear
- —
- Max coverage
- —
- Min lot
- 87,120 sf (~2.00 ac)
Mixed limited-commercial / institutional / residential center district (sec 300.002.004). Min lot size 2 acres (87,120 sf) (sec 300.002.004, 3/14/2006). Setback: all structures set back 75 ft from the CENTERLINE of Crawley Falls Road, Dalton Road, and Middle Road (NH Route…
- Front
- 40 ft
- Side
- 20 ft
- Rear
- 20 ft
- Max coverage
- —
- Min lot
- —
Overlay, not a base district: cluster developments may occur anywhere in the Residential/Agricultural District (sec 300.001.005 / 300.002.007). Internal building-lot standards: single-family frontage 75 ft; front setback 40 ft from edge of right-of-way; side and rear 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.
Brentwood 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 Brentwood (Rockingham County). A detached ADU can be up to 950 sf.
In Brentwood's R/A zone, ADUs follow the single-family setbacks: 75 ft front, 25 ft side, and 25 ft rear. Brentwood has 5 zoning districts in total — see the full table below. Confirm your exact zone with the town.