Washington County, UT Accessory Structures: ADU Rules (2026)
ADU rules in Washington County, UT, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Units per parcel
- 1 under 5 acres; max 4 total
- Extra unit rule
- 1 more per additional 5 acres
- Size range
- 1,500 to 3,500 sq ft by lot size
- Height range
- 25 ft to 35 ft by lot size
- Parking required
- 2 hard-surface spaces (1 if internal)
- Owner-occupancy
- 183 consecutive days/year to rent other unit
Summary
Washington County allows one ADU on any lot under 5 acres, with one more per additional 5 acres and a hard cap of four. Size scales with the underlying zone, from 1,500 to 3,500 square feet, and either the ADU or the main house must be owner-occupied to rent the other long-term.
B. General Provisions: 1. Number of accessory dwelling units per parcel. An accessory dwelling unit shall only be permitted on a parcel with a single family dwelling. Only one accessory dwelling unit is permitted on a lot or parcel that is zoned less than five (5) acres. On a lot or parcel that is zoned five (5) acres or more, one additional accessory dwelling unit may be approved for each additional five (5) acres above the base five (5) acres, in the sole discretion of the county. No more than four (4) accessory dwellings shall be allowed on a lot or parcel, except when zoned and approved in a planned development that complies will all applicable county ordinances. Only one accessory dwelling unit on the property may be rented.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: 2026 S-17: Code current through: Ord. 2026-1329-O, passed 8-18-2026).
Full Breakdown
1 caps density: "Only one accessory dwelling unit is permitted on a lot or parcel that is zoned less than five (5) acres," with one additional unit allowed per additional 5 acres above that base, in the county's sole discretion, and "no more than four (4) accessory dwellings shall be allowed on a lot or parcel" outside an approved planned development. Only one ADU per property may be rented. 5 acres, it rises again to 3,500 square feet and 35 feet. An internal ADU built entirely within a basement can use the whole basement footprint regardless of that cap.
3 requires two on-site, hard-surfaced parking spaces per ADU, one for an internal unit. 5 bars short-term rental use of either unit unless separately licensed under Section 10-13-23. D requires a complete application, fee, scaled site plan, floor plans, and utility plans, routed to the fire authority, health department, Building Division, and Public Works for approval before a building permit issues.
Violations & Fines
Section 10-13-18.E makes violations subject to "enforcement and penalties as outlined in Washington County zoning regulations," and specifically allows noncompliance to be "just cause for the denial of a business license application or renewal, or revocation of an existing business license" for a rented ADU. An application that cannot be brought into compliance after written notice is denied outright, and a withdrawn application forfeits its fee under Section 10-13-18.D.2.d.
Frequently Asked Questions
How many ADUs can I build on my Washington County lot?
How big can an ADU be in Washington County?
Do I have to live on the property to rent out my ADU?
Sources & Official References
Other rules in Washington County
How Washington County compares: Easiest Cities to Build an ADU·Compare Washington County to another location·View the Utah accessory structures overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.