ADU rules in Cranston

Since Ord. 2026-2 (City No. 12-25-01, passed 1-20-2026, approved 1-21-2026) Cranston allows one ADU per lot by right only in the three state circumstances: as a disability accommodation on an owner-occupied property, on a residential lot of 20,000 sq ft or more, or inside the existing footprint of the house or an existing accessory structure. A new detached ADU therefore works by right on lots of 20,000 sq ft or more (or as a disability accommodation); on smaller lots only a conversion of an existing garage or outbuilding without expanding its footprint qualifies. The ordinance has no special use permit route for other ADUs, and § 17.60.010(A)(3) bars residential occupancy of accessory uses except an ADU conforming with § 17.24.010, so anything else needs a variance from the Zoning Board of Review. Detached ADUs must meet the accessory-building setbacks of § 17.60.010(B).

An internal ADU (basement, attic or other conversion inside the existing footprint of the house) is allowed by right on any residential lot under § 17.24.010(F)(1)(iii), the common case. An attached ADU that expands the footprint, such as an addition, is allowed by right only on a residential lot of 20,000 sq ft or more or as a disability accommodation on an owner-occupied property; otherwise it needs a variance. The value is conditional because the footprint and lot-size gates decide additions.

Ord. 2026-2 replaced the old accessory family apartment cap (25 percent of the primary dwelling and 600 sq ft, one bedroom) with the statutory numbers, so the local cap equals the state floor in § 45-24-73(b)(1). Cranston also sets a 400 sq ft gross floor area minimum, allows at most two bedrooms, and allows one ADU per residential lot. Detached units must meet the accessory-building setbacks and lot coverage limits for the zoning district.

Owner occupancy applies only to the disability-accommodation ADU of § 17.24.010(F)(1)(i), which must be on an owner-occupied property; the owner signs an affidavit that the occupant is a parent or grandparent by blood or marriage, and the approval lasts only while the disabled resident lives there and until a change of ownership. ADUs on lots of 20,000 sq ft or more and ADUs within an existing footprint carry no owner-occupancy requirement. Ord. 2026-2 deleted the old accessory family apartment rules (yearly renewal, termination on any change of ownership).

The parking schedule requires one additional off-street parking space for an accessory dwelling unit, regardless of bedroom count. That is within the state cap of one space per ADU bedroom (§ 45-24-73(b)(2)(viii)). The city's ADU handout (created March 2025, before Ord. 2026-2) says one space per bedroom; the codified rule is one space.

ADUs meeting one of the three § 17.24.010(F)(1) circumstances are allowed by right, which under state law means an administrative building permit process only (§ 45-24-37(e)). Ord. 2026-2 deleted the old zoning board special permit for accessory family apartments and created no special use permit path for other ADUs, so an ADU outside the three circumstances, or one that misses a dimensional standard, needs a variance from the Zoning Board of Review under § 17.92.010 (the 9-1-2026 Plan Commission agenda lists such a variance for an ADU over a garage within the front and side setbacks).

Cranston's code repeats the state bar: ADUs shall not be offered or rented for tourist or transient use or through a hosting platform. Long-term rental is otherwise allowed for ADUs on 20,000 sq ft lots or within an existing footprint; state law bars restricting ADU tenants by family relationship or age. The disability-accommodation ADU is tied by affidavit to a parent or grandparent of the owner. ADUs may not be separated from the primary structure, subdivided, or sold as a condominium, ground lease, or tenancy in common. Cranston has no separate short-term rental licensing ordinance (eCode360 search, 0 hits for 'short-term rental(s)').