ADU rules in Johnston

Johnston's own ADU section (§ 340-24.1, added 2019) allows a detached ADU only inside an accessory structure, such as a garage or barn, that already existed before March 1, 2019; it makes no provision for a newly built detached cottage. State law overrides that for two by-right circumstances: a new detached ADU is allowed on any residential lot of 20,000 sq ft or more (R.I. Gen. Laws § 45-24-73(a)(2)), and an ADU inside the existing footprint of any existing accessory structure is allowed regardless of its age ((a)(3)), both through an administrative building permit (§ 45-24-37(e)). Conforming single-family lots in the R-40 and R-20 districts (40,000 and 20,000 sq ft minimums) therefore qualify for a new detached unit, while a new detached ADU on a smaller R-15, R-10 or R-7 lot is not allowed by right and would need zoning relief. Rhode Island directory convention: 'conditional' because the only by-right path for a new detached unit on an ordinary lot is the statute's 20,000 sq ft gate.

§ 340-24.1(D) permits an ADU 'within the principal dwelling unit structure' or 'attached to the principal dwelling unit structure and designed so that the appearance of the principal structure remains that of a one-family residence', in residential zones, where the principal use is a single-family dwelling and the property is owner-occupied. On its text that covers both internal conversions and footprint-expanding additions by right, with no lot-size gate. Town practice has read it more narrowly: a 2023 Zoning Board staff report (22 Rockcrest Lane) said § 340-24.1 permits ADUs only 'built in the existing structure, no [sic] an addition', although the board there granted only a side-yard variance for a 20 x 40 ft ADU addition, and earlier applicants sought a special use permit or use variance for attached in-law additions. Internal conversions are also by right under state law (§ 45-24-73(a)(3)).

§ 340-24.1 sets no floor-area cap for an ADU. The practical limits are form-based: a detached ADU must sit in a pre-March 1, 2019 accessory structure under the local text, an attached unit must keep the house looking like a one-family residence, and the district dimensional table limits accessory structures to 15 ft in height for single-family uses in R-20, R-15, R-10 and R-7 (25 ft in R-40) along with building coverage of 15 to 25 percent. With no local cap, Johnston satisfies the state requirement that any cap allow at least 900 sq ft or 60 percent of the principal dwelling (whichever is less) for a studio or one-bedroom ADU and 1,200 sq ft or 60 percent for a two-bedroom ADU (§ 45-24-73(b)(1)).

§ 340-24.1(B) requires that 'the property is owner-occupied', and § 340-24.1(E) makes it ongoing: before the building permit issues, the owner must record a lien in the land evidence records stating that if the property ceases to be owner-occupied the ADU will be removed. State law requires owner occupancy only for the disability-accommodation circumstance (§ 45-24-73(a)(1)); the 20,000 sq ft and existing-footprint circumstances carry no such condition, and § 45-24-73(b)(2)(xii) bars a municipality from revoking a legally established ADU's permitted status or requiring its disassembly upon transfer of title or occupancy, which conflicts with the removal lien. The value records the local rule as written.

§ 340-24.1 says nothing about parking. The general off-street table in § 340-29 requires 'two car spaces for each dwelling unit' for dwellings of three units or less more than 1,000 feet from transit service, and it has no ADU row, so the town could apply two spaces to the ADU as a second dwelling unit. Under R.I. Gen. Laws § 45-24-73(b)(2)(viii) a municipality may not require more than one off-street space per ADU bedroom, so a studio or one-bedroom ADU can be required to provide at most one space and a two-bedroom ADU at most two.

An ADU meeting § 340-24.1 'is permitted in residential zones' and proceeds to a building permit once the owner-occupancy lien is recorded, an administrative path; ADUs in any of the three state by-right circumstances also get an administrative building permit only (§ 45-24-37(e)). ADUs outside both, such as a new detached structure on a lot under 20,000 sq ft, need Zoning Board relief. The Table of Use Regulations still lists the pre-2019 'accessory family dwelling unit' as a special use (S) in R-40 through R-7, PD and PMUD, and § 340-147 allows accessory family dwelling units in conservation developments by special use permit only; past applicants used that route and use variances for in-law additions.

R.I. Gen. Laws § 45-24-73(b)(8) bars offering or renting an ADU for tourist or transient use (under 30 consecutive days) or through a hosting platform. Johnston's Chapter 265 Article I separately licenses residential units offered for tourist or transient use (annual $150 Town Clerk license with Building Official and Fire Department inspection), but that license cannot authorize short-term use of an ADU. § 340-24.1 does not restrict who may live in the ADU, so long-term rental to anyone is allowed while the owner occupies the property. The older 'accessory family dwelling unit' regime in § 340-4 and the use table limits occupancy to family members of the principal residence with an annual written representation to the Zoning Enforcement Officer; § 45-24-73(b)(2)(i) prohibits restricting ADU tenants by familial relationship, so that rule cannot be applied to ADUs.