ADU rules in Bristol

Bristol's Sec. 28-151(a), rewritten by Ord. No. 2025-07 (5-28-2025), copies the state's three by-right circumstances word for word: one ADU per lot on an owner-occupied property as a disability accommodation for family members, on a lot of 20,000 sq ft or more in residential use, or inside the existing footprint of the house or an existing accessory structure without expanding it. A detached ADU is therefore allowed by right on lots of 20,000 sq ft or more, or by converting an existing garage or shed within its footprint. A new detached ADU on a smaller lot (most R-6 to R-15 lots) needs a dimensional variance from the Zoning Board of Review under Sec. 28-151(d)(3). The town's definition in Sec. 28-1 expressly includes detached units and units in accessory structures.

An internal conversion (basement, attic or other space inside the existing house footprint) is allowed by right on any residential lot under Sec. 28-151(a)(3), and any attached form is by right on a lot of 20,000 sq ft or more under (a)(2). An addition that expands the house footprint on a lot under 20,000 sq ft falls outside the three circumstances and needs a dimensional variance from the Zoning Board of Review under Sec. 28-151(d)(3). By-right ADUs are building-permit matters under R.I. Gen. Laws 45-24-37(e).

Sec. 28-151(b)(2) sets the caps at exactly the statutory floor of R.I. Gen. Laws 45-24-73(b)(1): 900 sq ft or 60 percent of the principal dwelling's floor area, whichever is less, for a studio or one-bedroom ADU, and 1,200 sq ft or 60 percent, whichever is less, for a two-bedroom ADU. ADUs are limited to two bedrooms. Height, setbacks and coverage follow the accessory-structure dimensional standards of the zoning district (Sec. 28-151(b)(1)).

Owner occupancy appears in Sec. 28-151 only as part of the first by-right circumstance (an ADU on an owner-occupied property as a reasonable accommodation for family members with disabilities), mirroring R.I. Gen. Laws 45-24-73(a)(1). ADUs allowed under the lot-size circumstance (20,000 sq ft or more) or the existing-footprint circumstance carry no owner-occupancy requirement, and none is stated for ADUs approved by variance. The pre-2025 Bristol ordinance limited ADUs to owner-occupied single-family houses and family, caretaker or deed-restricted affordable occupants; Ord. No. 2025-07 struck that text.

Sec. 28-151(b)(2)d. requires one off-street parking space per bedroom of the ADU, the maximum R.I. Gen. Laws 45-24-73(b)(2)(viii) allows a municipality to require. A two-bedroom ADU therefore needs two additional spaces, on top of the house's own requirement.

ADUs meeting one of the three Sec. 28-151(a) circumstances are a permitted use approved through an administrative building permit only (R.I. Gen. Laws 45-24-37(e)). An ADU that does not meet Sec. 28-151 (for example a new detached unit or footprint-expanding addition on a lot under 20,000 sq ft) 'shall be reviewed through an application for a dimensional variance' under Sec. 28-151(d)(3), which the Zoning Board of Review decides after a noticed public hearing (Sec. 28-409). ADUs may also be included in new-dwelling and subdivision applications and considered through unified development review (Sec. 28-151(d)(1), (2)).

State law (R.I. Gen. Laws 45-24-73(b)(8)) bars offering or renting any ADU for tourist or transient use (under 30 days) or through a hosting platform, and Bristol's Sec. 28-151(c)(1) repeats the ban word for word. No occupant restriction applies: the former family, caretaker or affordable-only occupancy rules were struck by Ord. No. 2025-07, and state law bars familial or age restrictions on tenants. Bristol's zoning 'household' definition caps a group of unrelated persons at four, which applies to an ADU like any dwelling unit (relevant near Roger Williams University). The code has no local long-term rental registration.