ADU rules in Keene

A detached backyard ADU is allowed by right, with no zone gate and no hearing. Land Development Code § 8.4.2.A.1 defines an ADU to include "a detached ADU, located in or as a detached accessory building on the property", and § 8.4.2.A.2.c provides that ADUs "shall be permitted in any district and on any lot that contains a single-family dwelling", expressly including a lot whose single-family dwelling is legally nonconforming. That is broader than the state floor: RSA 674:73 requires a municipality to permit one detached ADU only in districts that allow single-family dwellings, while Keene keys the right to the presence of a single-family dwelling on the lot regardless of district. Keene reached this position in June 2023 with Ordinance O-2023-06, two years before the state mandated detached units. Only one ADU is allowed per lot (§ 8.4.2.A.2.a), and a detached unit is otherwise held to the district's ordinary dimensional standards, softened by an allowance to build within 10 feet of the rear lot line (§ 8.4.2.A.2.j.i).

An attached or internal ADU (a basement unit, an addition, or a conversion within the house) is allowed by right on the same terms as a detached one. Land Development Code § 8.4.2.A.1 covers "an attached Accessory Dwelling Unit (ADU), located within or attached to the principal dwelling unit", and § 8.4.2.A.2.c permits ADUs on any lot with a single-family dwelling in any district. Keene's old requirement of an interior door between the house and an attached ADU is gone: Ordinance O-2025-40, adopted March 19, 2026, deleted former § 8.4.2.A.2.e, and the June 2026 edition of the code now prints the section without it. The city's stated reason was "to come into compliance with recent changes to state law, specifically HB 577 which amended NH RSA 674:71 to :73", and RSA 674:72 III bars a municipality from limiting the choice of ingress and egress; at the March 5, 2026 public hearing Senior Planner Mari Brunner explained the door had been adding significant cost because it had to be fire rated to match the fire-rated separation wall. With that rule repealed, no standard anywhere in the code now treats an attached ADU differently from a detached one.

Land Development Code § 8.4.2.A.2.d caps an ADU at 1,000 square feet of gross floor area, and § 8.4.2.A.2.b limits it to 2 bedrooms. The size cap is more generous than the state default: RSA 674:72 VII sets 950 square feet "unless otherwise authorized by the municipality" and forbids any municipal cap below 750 square feet, so Keene's 1,000 square feet is a local expansion, not a restriction. The 2-bedroom limit is lawful because RSA 674:72 IX only forbids limiting an ADU to a single bedroom. Beyond floor area, § 8.4.2.A.2.j applies the overlying district's dimensions, siting, buildout and height requirements "as permitted by RSA 674:72, that would be required for a single-family dwelling without an ADU", which mirrors the no-extra-controls rule in RSA 674:72 I; where the district does not allow single-family dwellings at all, the district's own dimensional standards apply. The one dimensional break is § 8.4.2.A.2.j.i (echoed at § 1.3.3.A.4.e.iv, which lists "Accessory Dwelling Units, either detached or attached"), letting an ADU encroach to within 10 feet of the rear lot line on any lot where an ADU is permitted.

Keene requires the record owner to live on the property, and this survived both the March 2026 cleanup ordinance and the June 2026 recodification. Land Development Code § 8.4.2.A.2.h provides that "the record property owner shall occupy either the single-family dwelling or the ADU", and requires a sworn affidavit with the building permit application. RSA 674:72 VI expressly permits this and forbids a municipality from dictating which unit the owner occupies, so Keene's either-unit formulation is compliant; HB 577 did not disturb the owner-occupancy option, and Ordinance O-2025-40 deliberately removed only the interior-door and city-utility requirements while leaving this one in place. The obligation is ongoing, not just at application: § 8.4.2.A.2.i also requires a notice recorded at the Cheshire County Registry of Deeds "sufficient to notify successor owners that the ADU is subject to the City's Zoning Regulations", with evidence of recording filed before the permit issues, and Senior Planner Mari Brunner told the Planning Board on July 27, 2026 that a unit keeps ADU status "only if one of those two units is owner-occupied in perpetuity" and that losing owner occupancy turns the property into a duplex or 2-unit rental. The city's affidavit form tests occupancy as domicile plus a demonstrated intent to make the property the owner's principal place of physical presence, evidenced by voter registration, vehicle registration, driver's license, or children in local public schools. Section 8.4.2.A.1 separately requires the ADU to be "under the same ownership as the principal dwelling unit".

Land Development Code § 8.4.2.A.2.e states that "only 1 parking space shall be required for an ADU". Table 9-1 sets 1 space per unit for a single-family dwelling, so a house plus an ADU works out to 2 on-site spaces total; Keene cut its residential minimums to one space per unit with Ordinance O-2024-20-A (Feb. 20, 2025) and corrected the single-family row with Ordinance O-2025-09 (June 19, 2025). Both numbers sit inside the state ceilings: RSA 674:72 IV lets a municipality that requires parking for the principal dwelling require "up to one additional parking space for each accessory dwelling unit", and RSA 674:16 VII has barred any municipality from requiring "more than one residential parking space per unit" since September 13, 2025, with 2026 ch. 329 adding that a town may not require the space to be garaged effective September 13, 2026 (Keene's code mandates a garage nowhere). The scaled plot plan filed with the ADU building permit must show the location and number of required parking spaces. Keene's general parking relief provisions are aimed at principal uses rather than ADUs: § 9.2.7.A lets the Zoning Administrator grant an administrative reduction of up to 25 percent (raised from 10 percent by O-2025-40), and § 9.2.9 allows remote parking on a separate lot only with Zoning Administrator approval and never on a lot whose primary use is residential.

An ADU is a by-right accessory use reviewed administratively; there is no discretionary hearing. Land Development Code § 8.4.2.A.2.c permits ADUs on any lot with a single-family dwelling in any district, and Table 26-1 (Development Applications Decision Authority) lists no ADU application type at all, so neither the Zoning Board of Adjustment nor the Planning Board is involved. The city's own ADU page puts it plainly: ADUs "are now de-coupled from zoning and are allowed by right on any lot in the city with a single-family home." The route is a building permit, filed through the city's online permitting portal, with three ADU-specific submittals: a scaled and dimensional plot plan showing parking, driveways, buildings, setbacks, utilities and fences; the notarized owner-occupancy affidavit; and proof that the deed notice has been recorded at the Cheshire County Registry of Deeds, which must reach the Community Development Department before the permit issues. Where the lot is not on city sewer, § 8.4.2.A.2.f still requires a state-approved septic system plan before the permit issues, which tracks RSA 674:72 V.

Renting an ADU long term is the normal case in Keene, but the owner-occupancy rule means only one of the two units can be leased: Land Development Code § 8.4.2.A.2.h requires the record owner to occupy either the house or the ADU. Selling the ADU off is not possible either, because § 8.4.2.A.1 requires it to be "under the same ownership as the principal dwelling unit", and RSA 674:72 I independently prohibits subsequent condominium conveyance of an ADU separate from the principal unit unless the municipality allows it, which Keene has not. Short-term letting changed on June 18, 2026: Ordinance O-2026-02 replaced Keene's old "family" definition (which had allowed a group of four or fewer unrelated people, with no time limit) with "a natural person living alone or a group of natural persons living together as a single housekeeping unit that is primarily non-transient", where transient means "occupancy of a room or dwelling unit for less than 30 consecutive days or rental of a room or dwelling unit for a term of less than one month", and it amended "Dwelling Unit" to exclude transient occupancies. Because a single-family dwelling is defined as a building "designed, occupied, or intended for occupancy by 1 family", Senior Planner Mari Brunner told the Joint Planning Board and PLD Committee on July 13, 2026 that "any use that is transient for 30 days or less would no longer qualify as a family", that existing short-term rentals "would be non-conforming", and that staff are "holding out on any enforcement" while Ordinance O-2026-09 is pending. There is still no short-term rental use, definition or license anywhere in the code, and the same amendment removed Keene's only zoning occupancy cap, so a long-term tenant household of any size is now fine. A leased unit remains subject to Code of Ordinances ch. 18, art. IV housing standards for rental property (§ 18-15), though the emergency-contact posting rule in § 18-16 exempts owner-occupied primary residences; there is no rental registration or licensing regime.