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ADU rules in Rhode Island

Representative cities: Providence, Warwick.

Verify locally. Rhode Island is a MANDATORY statewide-code state — every city and town enforces the Rhode Island One & Two-Family Dwelling Code (IRC 2021 with Rhode Island amendments, effective Dec 1, 2025); local governments cannot weaken it. Watch the strict RI amendments to R105.2: the shed exemption is only 64 sq ft (vs. the IRC’s 120), and retaining-wall exemptions are 32 in (with cast-in-place concrete over 24 in always permitted). Permit fees follow a statewide valuation formula. Always confirm with your local building official. ADU rules below are drawn from official sources — always confirm with the issuing building department before designing or building.

ADU permit rule

Permit requiredGenerally allowedcity authority
Fee basis
Rhode Island statewide valuation-based fee formula (Providence minimum permit fee $125).
Typical timeline
Plan review; timeline varies by city (Providence 5–15 business days for most reviews).
Setback
Per local zoning; state law sets minimum allowances for ADUs in single-family zones.
Area threshold
Rhode Island requires municipalities to allow ADUs by right in single- and two-family zones; size/number set locally.
Exempt if
None — an ADU always requires a building permit.
Go / no-go
allowed
Rhode Island’s statewide ADU law requires every municipality to allow accessory dwelling units by right in single-family and two-family zones, so ADUs are broadly permitted. Local zoning still sets size, setbacks, parking, and owner-occupancy rules — verify with your city.
ADU official sources: Rhode Island Rules — One & Two-Family Dwelling Code (RICR 510) · ICC — Rhode Island Adopted Codes
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Frequently asked questions

Do I need a permit to build an ADU in Rhode Island?

Per Rhode Island rules, an ADU is "yes" for a permit and the authority is "city". Rhode Island’s statewide ADU law requires every municipality to allow accessory dwelling units by right in single-family and two-family zones, so ADUs are broadly permitted. Local zoning still sets size, setbacks, parking, and owner-occupancy rules — verify with your city. Always confirm with the issuing building department.

How big can an ADU be in Rhode Island?

Area threshold: Rhode Island requires municipalities to allow ADUs by right in single- and two-family zones; size/number set locally.

What are the ADU setbacks in Rhode Island?

Setback: Per local zoning; state law sets minimum allowances for ADUs in single-family zones.

How much does an ADU permit cost in Rhode Island?

Fee basis: Rhode Island statewide valuation-based fee formula (Providence minimum permit fee $125).

State-wide sources: Rhode Island Rules — One & Two-Family Dwelling Code (RICR Title 510) · ICC — Rhode Island Adopted Codes · Providence Department of Inspection & Standards

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