On October 1, 2026, a new Utah law changes what you can build behind your house. S.B. 284, passed in the 2026 session, added a section to the state code, § 10-21-304, that requires most Utah cities to allow a detached accessory dwelling unit (a backyard home, cottage or casita with its own kitchen and bath) on larger residential lots.
Until now, whether you could build one depended entirely on your city. Some allowed them, some allowed only an apartment inside the house, and some allowed nothing you could live in. From October 1 there is a statewide floor.
What the law requires
A covered city must adopt rules that permit a detached ADU on any lot or parcel that:
- is 11,000 square feet or larger,
- has a single-family home on it, and
- is in a zone where a single-family home is a permitted use.
Cities may go further and allow detached ADUs on smaller lots. Some already do: Salt Lake City has no minimum lot size at all.
Which cities it covers
The law applies to "specified municipalities": every city of the first, second, third or fourth class, and fifth-class cities with 5,000 or more people in a county of the first, second or third class. That covers 82 Utah cities, including Salt Lake City, West Valley City, Provo, West Jordan, Orem, Sandy, Ogden and St. George. Unincorporated county land is not covered.
What a city can't require
A covered city may not:
- require a conditional use permit for a detached ADU in a primarily residential zone;
- require more than one on-site parking space for a detached ADU under 650 square feet, or more than two for one of 650 square feet or more.
It must also give owners a way to convert a legally built accessory building, like a detached garage or studio, into a detached ADU, and it must require ADUs to meet building, health and fire codes.
What a city can still decide
The law sets a floor, not a design. Cities keep control over:
- size, height and lot coverage;
- setbacks, and design that fits the home;
- owner occupancy, meaning the owner lives in the house or the ADU;
- one ADU per lot.
A city may also prohibit a detached ADU that is larger than the home, sits in a front yard or on a recorded easement, lacks adequate utility access, or is rented for less than 90 consecutive days.
That is why the rules differ so much from one city to the next, and why we research each city's ordinance from its own documents. Utah ADU rules by city has what we've verified so far.
What to do now
- Check your lot. We find your county tax parcel, draw it, and apply the rule for your city.
- Read your city's rules, or call its planning office. Many cities are adopting or changing their ordinance right around October 1.
- Design the building. A backyard home still needs a building permit, and the drawings have to meet your city's size, height and setback rules.
The full text is in the enrolled bill, S.B. 284 (2026), and our summary of the law covers it section by section. This post is a summary, not legal advice.