Utah ADU laws, plainly: what S.B. 284 changed for backyard homes on October 1.

“Specified municipality” — does this cover my city?

The bill defines it as a city of the first, second, third or fourth class, or a fifth-class city with a population of 5,000 or more. In practice that is every city along the Wasatch Front and St. George. Small towns and unincorporated county land are not bound by this section, though counties have their own ADU rules.

Before S.B. 284: internal ADUs only

Utah's 2021 law, H.B. 82, required most cities to permit an internal ADU — a basement apartment or other space inside the main home — in most single-family zones. That is why basement apartments boomed first. H.B. 82 did not force cities to allow a detached backyard home; that stayed a local decision, and the answer varied from city to city.

What changed on October 1

Before October 1, many Utah cities allowed a detached ADU only as a conditional use — you applied, a planning commission held a hearing, neighbors commented, and the city could attach conditions or say no. Some cities restricted detached units to overlay zones; a few didn't allow them at all. On October 1 those discretionary steps went away on qualifying lots. The unit is now a permitted use, which means a building permit, not a hearing. Some cities are still rewriting their codes to match; Arena confirms the current text at the planning counter.

What didn't change

The city still decides the envelope. Setbacks, height, lot coverage, and design consistency with the main house all remain local. So does owner-occupancy — most cities require you to live in one of the two homes — and the 90-day minimum tenancy, which means an ADU is a long-term rental, not a nightly listing. That is why Arena keeps one page per city with that city's actual numbers, each marked verified, confirm-with-city, or moving-now.

The number that decides it: 11,000 square feet

A quarter acre is 10,890 sq ft — just under the line. Many older lots on the east benches, in Holladay, Sandy and Draper, clear it comfortably; many lots in the Avenues, Sugar House and newer subdivisions don't. Your county parcel record shows the figure. The ADU calculator asks for it, and if you're not sure, an Arena advisor pulls it when they run your address.

What the permit process looks like

Expect a zoning check on your parcel, a site plan, building plans engineered for Utah's seismic code (most of the Wasatch Front is Seismic Design Category D), utility connections, and inspections at the usual hold points. Arena runs the zoning check as step one of every project. Permitting typically runs 3–5 weeks and construction 6–8 weeks after that.

Every service-area city, in one place

Salt Lake County

• Salt Lake City — Salt Lake City already allows ADUs. The new law removes the discretion.
• Draper — Draper's rules are proportional — and that's the part worth reading.
• Sandy — Sandy runs ADUs through a Special Use Approval — and that's exactly what the statute targets.
• South Jordan — South Jordan's own minimum lot is larger than the state's — so the state threshold is what changes here.
• West Jordan — West Jordan is one of the few Wasatch Front cities without an owner-occupancy rule on the books.
• Herriman — Herriman is still writing its detached ADU ordinance — and the clock runs out October 1.
• Riverton — Riverton regulates the building, not the dwelling — ADUs sit inside its accessory-structure rules.
• Murray — Murray asks for a recorded affidavit before it will even accept your application.
• Holladay — Holladay has the lot sizes. The question is what its amended ordinance says.
• Cottonwood Heights — Today a detached ADU here is a conditional use. On October 1 that becomes illegal.

Utah County

• Lehi — Lehi has already passed its new rules — and eligibility jumped about 20%.
• American Fork — American Fork's older core has the lots. The ordinance is being amended now.
• Provo — Provo allowed detached ADUs only inside overlay zones. That ends October 1.
• Orem — Orem did not allow detached ADUs at all. On October 1, it must.
• Pleasant Grove — Pleasant Grove is amending its ordinance ahead of the October 1 deadline.

Davis County

• Bountiful — Bountiful has an ADU ordinance already — the detached rules are what's moving.
• Layton — Layton's detached minimum is 6,000 sq ft — already well under the state line.

Summit County

• Park City — Park City is the hardest market on this list — and the 90-day rule is why.

Weber County

• Ogden — Ogden's 800 sq ft cap is the number that shapes your plan choice.

Washington County

• St. George — St. George usually requires a conditional use permit for detached units — and the statute overrides it.