On an owner-occupied property as a reasonable accommodation for family members with disabilities; or

On a lot with a total lot area of 20,000 sq. ft. or more for which the primary use is residential; or

Where the proposed ADU is located within the existing footprint of the primary structure or existing accessory attached or detached structure and does not expand the footprint of the structure.

The accessory dwelling unit shall be designed for year-round occupancy. The accessory dwelling unit shall be provided with a safe and adequate water supply as defined in the subdivision regulations and an on-site wastewater treatment system approved by the Rhode Island Department of Environmental Management. A separate OWTS is not required if the existing system has sufficient capacity and is approved for the expanded use. The accessory dwelling unit shall also have adequate protections for stormwater runoff as necessary.

Any existing principal residence and accessory dwelling unit shall comply with all requirements of the Rhode Island State Building Code, the Rhode Island Housing Maintenance and Occupancy Code, and other Federal, State and local codes, ordinances and regulations and all other applicable provisions of this chapter.

All such accessory dwelling units shall be required to obtain a building permit and certificate of occupancy, whether or not any construction is required.

Detached accessory dwelling units shall comply with all dimensional zoning regulations for an accessory structure in the district in which the lot is located. Detached ADUs located within legally existing accessory structures may be permitted even if the structure does not meet current setback requirements, provided that no expansion or enlargement of the structure is proposed.

Short-term residential rentals are prohibited in accessory dwelling units. For purposes of this section, "short-term residential rentals" means the use of any accessory dwelling unit for occupancy for less than a 30-consecutive-day term of tenancy, whether on a short-term or long-term basis, including any occupancy by an employee or guests of a business entity for less than 30 consecutive days where payment for the accessory dwelling unit is contracted for or paid by the business entity.

The floor area of an accessory dwelling unit shall not exceed the following thresholds:

For a one-bedroom ADU: 900 square feet or 60% of the floor area of the principal dwelling, whichever is less.

For a two-bedroom ADU: 1,200 square feet or 60% of the floor area of the principal dwelling, whichever is less.

An ADU which meets the requirements of RIGL § 45-24-31 and § 45-24-73(a) shall be permitted through an administrative building permit process only.

ADUs shall be allowed as part of applications for new primary dwelling units or subdivisions. For proposed ADUs that are part of a larger development proposal, such ADUs shall not be counted toward density of the proposal. Any application that includes ADUs may be considered through a unified development review process.