Compare ADU rules across New Hampshire

A detached ADU is contemplated by the ordinance but is gated behind a discretionary hearing. § 235-41A(4) provides that an ADU 'may be located in the same building as the principal dwelling unit or in a separate detached structure such as a garage or barn,' with any new structure meeting the district's dimensional standards. Table I (235 Attachment 2) then marks 'Accessory dwelling unit' as E, special exception, in every district that permits a single-family dwelling: RR1, RR2, RS, SFR, RG, RA, CR, UC and C; it is N, not permitted, in the Industrial Park, Industrial and Airport Industrial districts, which do not allow single-family dwellings either. A second local wrinkle is that the § 235-13 definition is narrower than § 235-41A(4): it describes an ADU as a unit 'within or attached to a single-family dwelling, or located in a legally existing accessory structure on the same lot,' which read literally would allow a garage or barn conversion but not a newly built backyard cottage. Both the special exception gate and that definitional limit are in conflict with state law: RSA 674:73, as amended by 2025 NH Laws ch. 197 (HB 577) effective July 1, 2025, now reads 'A municipality shall permit one detached accessory dwelling unit,' and RSA 674:72, I requires one ADU, attached or detached, to be allowed 'as a matter of right.'

Ordinance read August 2026

An attached or internal ADU runs the same special exception gauntlet: Table I gives 'Accessory dwelling unit' a single E rating that covers both forms, so a basement, attic or addition conversion needs the same Zoning Board of Adjustment approval as a detached unit. § 235-41A(4) allows the ADU 'in the same building as the principal dwelling unit,' and § 235-41A(5) requires an ADU built into an addition to share the existing dwelling's utilities (telephone and television excepted), while a detached unit may take separate municipal water and sewer connections. § 235-41A(7) adds that 'An interior door must be provided between the principal dwelling unit and the accessory dwelling unit, if attached.' That requirement now sits badly with state law: ch. 197 repealed and reenacted RSA 674:72 in full, and the reenacted paragraph III says an attached ADU shall have either an independent means of ingress and egress or ingress and egress through a shared common space and that 'the municipality shall not limit the choice of ingress and egress.' The owner-occupancy condition, the 1,000 square foot cap and the extra parking space apply identically to an attached unit.

Ordinance read August 2026

As Laconia's ordinance is written, an ADU needs a special exception from the Zoning Board of Adjustment in every district where it is allowed. Table I rates 'Accessory dwelling unit' as E citywide, § 235-26 defines E as permitted by special exception, and § 235-70C(1) gives the ZBA the power to hear and decide special exceptions 'specifically authorized in the Table of Permitted Uses.' That means a noticed public hearing with certified-mail abutter notice at least five days out (§ 235-69C(3)), eight written findings including that the use 'will not create hazards to the health, safety, or general welfare of the public, not be detrimental to the use of or out of character with the adjacent neighborhood' (§ 235-70C(2)), a concurring vote of three members (§ 235-69C(5)), and the ZBA's power to attach conditions (§ 235-70C(4)). The zoning and planning fee schedule adopted 2-10-2020 charges $125 for zoning applications plus abutter notice costs. On top of that, § 235-41A(13) requires an application approved by the Planning Department, a building permit for all construction, and a certificate of occupancy before occupancy. The city's own short-term lodging application still describes an ADU as one 'created by the granting of a Special Exception by the Zoning Board of Adjustment,' which is good evidence this is the live practice. Since July 1, 2025, however, RSA 674:72, I has required one ADU to be allowed 'as a matter of right' and barred 'other controls beyond what would be required for a single-family dwelling without an accessory dwelling unit,' so the special exception requirement is preempted; Laconia amended § 235-41 and Table I on 9-8-2025 and again on 3-9-2026 without changing it.

Ordinance read August 2026

Rochester's own ordinance still sends every detached unit to the Zoning Board of Adjustment. § 275-23.2A(1)(a) allows an accessory apartment where the Tables of Uses permit it, then adds that if the unit is detached from the single-family dwelling it must be approved by a special exception, and (b) requires a detached unit to be similar in architectural style to the house. That text is the 2017 version and predates New Hampshire's 2025 rewrite. RSA 674:73, as amended by 2025 Laws ch. 197 (HB 577, effective July 1, 2025), now reads 'A municipality shall permit one detached accessory dwelling unit,' and RSA 674:72, I requires one ADU, 'which may be either attached or detached,' to be allowed 'as a matter of right' in all zoning districts that permit single-family dwellings, with no added controls for lot size, setbacks, aesthetics, design review, frontage, or space limitations. Rochester has not conformed Chapter 275: the eCode360 text is current through 10-07-2025 and the Planning Board was still workshopping a conforming amendment in April and May 2026. Treat a detached backyard unit as lawful as of right under the statute, but expect the counter to point at the special-exception track until the city amends.

Ordinance read August 2026

An attached or internal unit (basement, addition, or space over an attached garage) is the mainstream path, but the district matters. Table 18-A lists 'Apartment, accessory (accessory use)' as permitted by right in Residential-2, Agricultural, Neighborhood Mixed-Use, Downtown Commercial, Office Commercial, and Highway Commercial, and as a special exception in Residential-1 and Hospital Special; it is not listed at all in General Industrial, Recycling Industrial, or Airport Special. So R2, the dense older neighborhoods, can add one over the counter, while R1, the lower-density single-family district with a 10,000 sq ft minimum lot, still requires a Zoning Board hearing under the unamended table. § 275-23.2A(1)(b) limits the use to single-family dwellings only, (f) allows just one per lot, and (e) requires an interior door between the two units when the accessory apartment is inside the house. RSA 674:72, I now requires as-of-right treatment in every district that permits single-family dwellings, which in Rochester means R1, R2, AG, NMU, OC, HC, and HS, so the R1 and HS special-exception entries are preempted; the 2025 reenactment also dropped the old statutory permission to require an interior door and added that a municipality 'shall not limit the choice of ingress and egress' (RSA 674:72, III).

Ordinance read August 2026

It depends on the unit type and the district. An attached accessory apartment in R2, AG, NMU, DC, OC, or HC is administrative: § 275-23.2A(1)(j) exempts it from site plan review and asks only that a letter of intent be submitted to the Building Inspector to confirm the conditions are met, alongside the building permit § 275-3.3A requires from the Director of Building, Zoning, and Licensing Services and the certificate of occupancy under § 275-3.3E. Any detached unit, and any accessory apartment in the R1 or Hospital Special district, goes to the Zoning Board of Adjustment for a special exception under Article 22, which means a noticed public hearing, the base criteria in § 275-22.2, and the Board's power under § 275-22.1G to impose conditions such as increased setbacks, extra screening, or a smaller building than the ordinance would otherwise allow. RSA 674:72, I as reenacted in 2025 makes one ADU allowable 'as a matter of right' with no controls beyond those for a single-family dwelling, so the special-exception track is preempted in substance, but it is what the ordinance on the books prescribes and what the ZBA docket still reflects in 2026. One genuine local benefit: § 275-27.3G(5) waives impact fees for accessory dwelling units.

Ordinance read August 2026