ADU rules in Rochester

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.

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).

§ 275-23.2A(1)(d) says the accessory apartment may not exceed 800 square feet, and (c) says it must be two bedrooms or less. Those are still the numbers Rochester enforces: ZBA case Z-26-6, heard April 8, 2026, sought a variance from § 275-23.2A(1)(d) to permit a 924 sq ft accessory dwelling unit where 800 sq ft is permitted, at 8 Julia Avenue in the Agricultural zone. The 800 sq ft cap survives the 2025 state rewrite. RSA 674:72, VII sets a default statewide ceiling of 950 square feet 'unless otherwise authorized by the municipality' and separately provides that a municipality 'may not restrict the total living space to less than 750 square feet,' so any local cap between 750 and 950 is lawful, and 800 sits inside that band. The two-bedroom limit is lawful too: RSA 674:72, IX bars only a one-bedroom limit. There is no ADU-specific lot-size gate; the R1 and R2 minimum lot areas (10,000 and 6,000 sq ft) and the 30% maximum building footprint and 35% maximum lot coverage in Table 19-A apply to the property as a whole. Rochester's Planning Board discussed raising the cap to 900 sq ft in April 2026, with a possible 900 to 1,200 sq ft band under special conditions, but no amendment has been adopted.

Yes, and unlike Rochester's other ADU restrictions this one is not preempted. § 275-23.2A(1)(g) requires that the owner of the property occupy one of the dwelling units and demonstrate that one of the dwelling units is his or her principal place of residence. It reads as a standing condition of the use rather than a one-time test at application, and it does not dictate which unit, so living in the accessory apartment and renting the main house is fine. New Hampshire's 2025 ADU expansion deliberately preserved this authority: RSA 674:72, VI, as reenacted by HB 577, still provides that 'A municipality may require owner occupancy of one of the dwelling units, but it shall not specify which unit the owner must occupy,' and expressly permits the municipality to require proof of principal residence and to adopt reasonable enforcement regulations. Homeowners hoping the 2025 law swept owner occupancy away should not rely on that; it did not.

§ 275-23.2A(1)(h) requires that at least one parking space be provided for the accessory apartment. That sits on top of the two off-street spaces § 275-26.1A requires for a single-family dwelling, so a Rochester house with an accessory apartment needs three spaces. Each space serving a single- or two-family use must be at least nine by 18 feet (§ 275-26.1C), and § 275-5.2B(1) keeps parking areas out of the front setback and off the area forward of the front facade except within a clearly defined driveway. One added space is exactly the ceiling the state allows: 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 adds that required spaces 'may be provided either on-site or at a legally dedicated off-site location, at the property owner's discretion,' an option Rochester's own text does not mention.

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.

Long-term rental is fine and Rochester has no short-term rental ordinance, no rental registry, and no ADU-specific lease-length rule; a full-text search of the City Code, all chapters and not just zoning, turns up no short-term rental, vacation rental, or rental licensing provisions. The practical limit is owner occupancy: because § 275-23.2A(1)(g) requires the owner to live in one of the two units and prove it is their principal residence, only one of the two can be rented out. Nightly rental is riskier than it looks. § 275-2.2 defines a dwelling so as to exclude structures intended for transient or short-term occupancy, defines a lodging facility as one offering short-term overnight accommodations for paying transient guests whose visitors have their primary residence elsewhere, and treats a bed-and-breakfast as a distinct owner-occupied commercial lodging use, so renting an accessory apartment nightly invites reclassification into a lodging use that the Tables of Uses regulate separately by district. § 275-23.1C(1) adds that accessory uses to residential uses should be established for the benefit of the resident, residential development, and guests, and not for commercial purposes, though § 275-2.1F makes 'should' advisory rather than mandatory. Selling the unit off separately is barred: RSA 674:72, I prohibits subsequent condominium conveyance of an accessory dwelling unit separate from the principal dwelling unit 'unless allowed by the municipality,' and Chapter 275 contains no such allowance.