Building an ADU in Rhode Island

When state law lets you build an ADU by right

Rhode Island does not require towns to allow an ADU on every lot. Instead, 45-24-73 says "one accessory dwelling unit (ADU) per lot shall be allowed by right" in three situations:

• on an owner-occupied property, as a reasonable accommodation for family members with disabilities;
• on a lot of 20,000 square feet or more whose primary use is residential;
• where the ADU sits within the existing footprint of the main house or an existing attached or detached accessory structure, and does not expand that footprint.

An ADU that fits one of these cases (and the state definition) is a permitted use in all residential zoning districts. State law says it "shall be permitted through an administrative building permit process only."

Outside those three cases, your town's zoning sets the rules and process. A town must still allow ADUs as part of applications for new homes or subdivisions, and it cannot count those ADUs toward the density of the larger proposal. An ADU application cannot be reviewed as a minor or major land development project on that basis alone, and the statewide limits below still apply. [1][2]

What counts as an ADU

State law defines an ADU as a residential living unit on the same lot as a legally established single-family or multifamily home. It provides "complete independent living facilities for one or more persons."

It can be a detached unit, a unit in an accessory structure such as a detached garage, or a unit that is part of an expanded or remodeled main home. [3]

What your town can and can't require

A town may set a maximum ADU size, but the cap must allow at least:

• 900 square feet or 60% of the main home's floor area, whichever is less, for a studio or one-bedroom ADU;
• 1,200 square feet or 60% of the main home's floor area, whichever is less, for a two-bedroom ADU.

For any ADU application, your town cannot:

• restrict tenants by family relationship or age (unless needed to meet a federal affordability subsidy);
• charge application or permit fees higher than for a new single-family home;
• discriminate against groups protected by state and federal fair housing laws;
• require infrastructure improvements for the ADU, such as separate water or sewer lines or more septic capacity, unless a state agency, the building code, or capacity or upgrade needs require them;
• set dimensional or other standards stricter than those for an accessory structure in the same district;
• require extra lot area, frontage or width to fit an ADU on a conforming or legal nonconforming lot;
• require zoning relief for an ADU within the existing footprint of a legal nonconforming building, just to address that existing nonconformity;
• require more than one off-street parking space per ADU bedroom;
• limit ADUs to lots that already have a house, or ban them in new-home or subdivision applications;
• stop a compliant ADU from having up to two bedrooms;
• require the ADU to be rented only to low- or moderate-income households, except in inclusionary zoning or comprehensive permit applications;
• revoke a legally established ADU's status, or make you take it down, when the property is sold or the occupants change.

Local limits or moratoriums on new homes in residential zones cannot be used to restrict ADUs. Towns may also exempt ADUs from all or part of utility assessment or tie-in fees. [1]

Garage conversions and existing buildings

Converting space inside an existing building is one of the three by-right cases, as long as you don't expand the footprint. That covers the main house and an existing attached or detached accessory structure, such as a garage. The state definition also lists a unit in a detached garage as one form an ADU can take.

If the building is a legal nonconforming structure, the town cannot require zoning relief for an ADU inside its existing footprint just to deal with that existing nonconformity. See our garage conversion guide for the general steps, and confirm building code requirements with your local building official. [1][3]

HOAs and condo associations

Private restrictions on ADUs set by condominium associations, homeowners associations or similar bodies are "void as against public policy" when they conflict with 45-24-73 or the state ADU definition. Association covenants that allow ADUs are treated as complying. [1]

Renting it out

State law says ADUs "shall not be offered or rented for tourist or transient use or through a hosting platform." RIHousing sums it up: "the law prohibits short-term rentals."

Towns cannot restrict ADU tenants by family relationship or age (except as needed to meet a federal affordability subsidy), and cannot require income-restricted renters except in inclusionary zoning or comprehensive permit cases. [1][4]

Help paying for an ADU

RIHousing offers an FHA 203(k) loan that covers buying or refinancing a home plus building an attached or interior ADU, such as a garage or basement unit. It does not finance detached ADUs such as small cottages or tiny homes.

The project must be finished within 12 months. You must take RIHousing's 203(k) homebuyer education class before closing (offered online for $15) and use an FHA-approved Rhode Island 203(k) consultant. More ideas are in our ADU financing guide. [4]

Check your town's rules

Because only three cases are by right statewide, your town's zoning ordinance matters a lot in Rhode Island. RIHousing notes that "each town may have its own specific regulations." Ask your city or town zoning and building offices which rules apply to your lot.

The full state law is on the Rhode Island General Assembly website. Our ADU permit process guide covers the general steps. [1][4]

Rhode Island laws to know

• R.I. Gen. Laws 45-24-73

  Sets the three by-right cases and statewide limits on how towns treat any ADU application: size caps, fees, parking, bedrooms, HOA rules and short-term rentals. [1]

• R.I. Gen. Laws 45-24-37(e)

  Makes an ADU that meets 45-24-73(a) a permitted use in all residential zones, approved through an administrative building permit process only. [2]

• R.I. Gen. Laws 45-24-31(2) (definition)

  Defines an ADU as a unit with complete independent living facilities on the same lot as a legally established single-family or multifamily home. [3]

Questions people ask