ADU rules in Rochester

Rochester's own ordinance still sends every detached unit to the Zoning Board of Adjustment. Section 275-23.2A(1)(a) allows an accessory apartment where the Tables of Uses permit it, then adds that "if the accessory dwelling 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 is the 2017 text and it predates New Hampshire's 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 every district that permits single-family dwellings, with no added controls for lot size, setbacks, aesthetics, design review, frontage, or space limitations, so both the special-exception step and the architectural-style condition are preempted. Since August 31, 2026 the conflict clearly covers conversions too: 2026 Laws ch. 210 (HB 1079) rewrote RSA 674:71, III so a unit completely contained within a preexisting detached structure is a detached unit, which is how Rochester has always drawn the line anyway (its trigger is physical detachment from the house, not the statutory definition), so a garage or barn conversion is a detached unit under both texts and RSA 674:73 plus the conversion mandate in RSA 674:72, XI reach it squarely. Rochester has not conformed Chapter 275: the eCode360 text is still codified through 10-07-2025 and no ADU amendment appeared on a Planning Board, Codes and Ordinances Committee, or City Council agenda between April 2026 and September 3, 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 (a basement, an addition, or space over a garage that is attached to the house) 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 allowed 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. Section 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). Since August 31, 2026 RSA 674:71, II defines an attached unit as one "within or attached to the principal dwelling unit" and nothing more, so a unit inside a freestanding garage or barn is no longer an attached unit under state law; for that project read the detached row.

Section 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 Section 23.2.A(1)(d) "to permit a 924 s.f. accessory dwelling unit where 800 s.f. is permitted" at 8 Julia Avenue in the Agricultural zone. The 800 sq ft cap survives the 2025 state rewrite and 2026 Laws ch. 210 did not disturb it: 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, because 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. The Planning Board discussed raising the cap to 900 sq ft in April 2026, with a possible 900 to 1,200 sq ft allowance for conversions of existing barns, garages, or commercial space, and the May 4, 2026 minutes record that the change was "progressing to the City Council," but the Planning Updates of June 1, June 15, July 6, August 3, and August 17, 2026 never mention it again and no ADU amendment has reached a City Council or Codes and Ordinances agenda through September 3, 2026.

Yes, and unlike Rochester's other ADU restrictions this one is not preempted. Section 275-23.2A(1)(g) requires that "the owner of the property must occupy one of the dwelling units and the owner must demonstrate that one of the dwelling units is his/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. 2026 Laws ch. 210 amended only RSA 674:71, II and III and RSA 674:72, XI, so it left this authority untouched. Homeowners hoping the recent state laws swept owner occupancy away should not rely on that; they did not.

Section 275-23.2A(1)(h) requires that "at least one parking space must be provided for the unit," and 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. What Rochester may no longer enforce is the two-space baseline for the house. Section 275-26.1A still reads "Minimum off-street parking requirements for single-family dwellings are two spaces," but since September 13, 2025 RSA 674:16, VII has provided that a local legislative body "may regulate accessory parking for vehicles, but shall not require more than one residential parking space per unit," so the lawful maximum for a Rochester house with an accessory apartment is two spaces in total, not the three the ordinance text adds up to. Effective September 13, 2026, 2026 Laws ch. 329 also bars a municipality from requiring "that the parking space per unit be garaged"; Chapter 275 contains no garage mandate, so that clause changes nothing in Rochester. Each space serving a single- or two-family use must be at least nine by 18 feet (Section 275-26.1C), and Section 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.

It depends on the unit type and the district. An attached accessory apartment in R2, AG, NMU, DC, OC, or HC is administrative: Section 275-23.2A(1)(j) exempts it from site plan review and asks only that "a letter of intent must be submitted to the Building Inspector to ensure that the above conditions are met," alongside the building permit Section 275-3.3A requires from the Director of Building, Zoning, and Licensing Services and the certificate of occupancy under Section 275-3.3E. Any detached unit, which since August 31, 2026 includes a unit inside a preexisting detached garage or barn under RSA 674:71, III, 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, meaning a noticed public hearing, the base criteria in Section 275-22.2, and the Board's power under Section 275-22.1G to impose "such additional conditions as it finds reasonably appropriate," including increased setbacks and screening. 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. Rochester publishes no ADU-specific application form: the Planning and Development forms library (39 forms, inventoried September 6, 2026) offers only the generic Special Exception Application and Variance Package. One genuine local benefit: Section 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 whole City Code on September 6, 2026 returned zero hits for "short-term rental," "short-term rentals," and "rental license" across the Code, the New Laws bank, and Public Documents. The practical limit is owner occupancy: because Section 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. Section 275-2.2 defines a dwelling 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. Section 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 Section 275-2.1F makes "should" a preferred rather than a required course of action. 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.