Build an ADU in Franklin.
New Hampshire's HB 577 lets you add one accessory dwelling unit on your single-family lot in Franklin — by-right. A detached ADU can be up to 950 sf, and ADU setbacks match your lot's single-family setbacks.
11 districts
Each district's single-family setbacks — which your ADU follows. The primary residential district is highlighted.
Verified against the official Franklin zoning ordinance · source · 2026-07-07
- Front
- 30 ft
- Side
- 25 ft
- Rear
- 25 ft
- Max coverage
- —
- Min lot
- 40,000 sf (~0.92 ac)
Principal single-family district: 'an area of predominantly preexisting single-family homes... Min lot TIERED BY UTILITIES: 15,000 sf with off-lot City sewer AND water; 20,000 sf with sewer OR water; 40,000 sf with on-lot sewer and water — conservative no-utilities tier recorded.
- Front
- 40 ft
- Side
- 25 ft
- Rear
- 25 ft
- Max coverage
- —
- Min lot
- 87,000 sf (~2.00 ac)
Countryside/rural residential district (305-12.A(1)). Min lot TIERED BY UTILITIES: 65,500 sf with off-lot City sewer AND water; 65,500 sf with sewer OR water; 87,000 sf with on-lot (private) sewer and water — conservative no-utilities tier recorded.
- Front
- 40 ft
- Side
- 20 ft
- Rear
- 20 ft
- Max coverage
- —
- Min lot
- 40,000 sf (~0.92 ac)
Low-density residential for land that is or may be served by municipal facilities (305-12.A(3)). Min lot TIERED BY UTILITIES: 20,000 sf with off-lot City sewer AND water; 30,000 sf with sewer OR water; 40,000 sf with on-lot sewer and water — conservative tier recorded.
- Front
- 20 ft
- Side
- 15 ft
- Rear
- 15 ft
- Max coverage
- —
- Min lot
- 40,000 sf (~0.92 ac)
High-density residential where central water and sewer are available and nearest municipal/business facilities (305-12.A(4)). Min lot TIERED BY UTILITIES: 10,000 sf with off-lot City sewer AND water; 15,000 sf with sewer OR water; 40,000 sf with on-lot sewer and water —…
- Front
- 15 ft
- Side
- 15 ft
- Rear
- 15 ft
- Max coverage
- —
- Min lot
- 40,000 sf (~0.92 ac)
Already-developed neighborhoods of predominantly 1-3 family homes (305-12.A(5)). Min lot TIERED BY UTILITIES: 15,000 sf with off-lot City sewer AND water; 20,000 sf with sewer OR water; 40,000 sf with on-lot sewer and water — conservative tier recorded.
- Front
- 15 ft
- Side
- 15 ft
- Rear
- 20 ft
- Max coverage
- —
- Min lot
- 30,000 sf (~0.69 ac)
Business/commercial plus restricted residential uses near key locations and major highways (305-12.B(1)). Min lot TIERED BY UTILITIES: 10,000 sf with off-lot City sewer AND water; 20,000 sf with sewer OR water; 30,000 sf with on-lot sewer and water — conservative tier recorded.
- Front
- 20 ft
- Side
- —
- Rear
- 20 ft
- Max coverage
- —
- Min lot
- —
Downtown district ('Franklin Downtown Section', 305-12.B(2)). Min lot area: NR (No Regulation) on ALL utility tiers — no minimum lot size. Front yard 20 ft carries table footnote 1: 'Maintain front lot lines in developed areas' (build-to expectation downtown).
- Front
- 50 ft
- Side
- 25 ft
- Rear
- 50 ft
- Max coverage
- —
- Min lot
- 100,000 sf (~2.30 ac)
High-value industrial campus district (305-12.C(1)). Min lot TIERED: 40,000 sf with off-lot City sewer AND water; 100,000 sf otherwise — conservative tier recorded. Frontage >= 80 ft No lot-coverage limit.
- Front
- 25 ft
- Side
- 25 ft
- Rear
- 40 ft
- Max coverage
- —
- Min lot
- 100,000 sf (~2.30 ac)
Research/development and light industrial uses that will not disturb neighboring properties (305-12.C(2)). Min lot TIERED: 40,000 sf with off-lot City sewer AND water; 100,000 sf otherwise — conservative tier recorded.
- Front
- 50 ft
- Side
- 25 ft
- Rear
- 25 ft
- Max coverage
- —
- Min lot
- 225,000 sf (~5.17 ac)
Limited to low-density residential, agriculture and open-land uses; purpose is to prevent intensive development of land unsuitable due to lack of utilities, poor soil, steep slope or flooding (305-12.D).
- Front
- 50 ft
- Side
- 50 ft
- Rear
- 50 ft
- Max coverage
- 30% impervious
- Min lot
- 108,900 sf (~2.50 ac)
Environmentally sensitive district surrounding Webster Lake (305-12.E). Min lot 108,900 sf (2.5 acres) on ALL utility tiers (no tiering). Frontage >= 200 ft The 30% coverage figure is the Webster Lake Overlay District cap: 'The impervious area of any building lot is limited…
Form-based and downtown districts may use build-to lines instead of fixed setbacks (shown as “—”); verify your parcel's district before you build.
Franklin 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 Franklin (Merrimack County). A detached ADU can be up to 950 sf.
In Franklin's RS zone, ADUs follow the single-family setbacks: 30 ft front, 25 ft side, and 25 ft rear. Franklin has 11 zoning districts in total — see the full table below. Confirm your exact zone with the town.