Utah's new detached ADU law: what SB 284 changes for Davis and Weber County

What SB 284 requires, and by when

Starting October 1, 2026, new Utah Code section 10-21-304 requires every covered city to permit a detached accessory dwelling unit on any lot or parcel of 11,000 square feet or larger that contains a single-family home, wherever that home is itself a permitted use. Coverage reaches down to cities of 5,000 residents in counties the size of Davis and Weber — which takes in the cities where most homeowners here live, from Bountiful and Farmington up through Layton, Syracuse, Roy, and Ogden. The rest of the bill took effect May 6, 2026; the detached-ADU section carries an October 1 effective date, with compliant city ordinances required by then.

Three protections in the statute matter most:

• Permitted use, not conditional use. In a primarily residential zone, the city cannot route your detached ADU through a conditional use permit — the discretionary hearing where backyard projects historically went to die. Meet the ordinance and the application proceeds.
• A parking ceiling. No more than two on-site stalls for a unit of 650 square feet or larger; no more than one for a unit under 650.
• A mandatory conversion path. Each city’s ordinance must include a process for converting a legally built accessory structure — an existing garage or shop — into a dwelling unit, subject to setbacks and building, health, and fire codes.

What your city still controls

SB 284 sets a floor, not a free-for-all. The statute expressly lets cities regulate setbacks, height, structure size, and lot coverage; require the ADU’s design to be consistent with the main house; prohibit units larger than the main house, in a front yard, or in a recorded easement; require the owner to live in either the house or the ADU; cap lots at one ADU; prohibit rentals shorter than 90 consecutive days; and deny a unit where sewer, culinary water, electrical, or storm-water capacity genuinely is not there.

One carve-out is worth reading twice: development agreements a city signed on or before May 6, 2026 are not superseded. Some master-planned subdivisions along the Wasatch Front will stay restricted no matter what the statute says — check your plat before you sketch anything.

As of mid-July 2026, local coverage had focused on Utah County — Lehi was first to adopt an amended ordinance, with Orem and Provo still working through theirs — and almost nothing spoke to Davis and Weber lots. Your own city’s amended ordinance — required to be in place by October 1, 2026 — is the document that decides your setbacks, your height limit, and whether you must live on the property.

The quarter-acre catch

A quarter acre is 10,890 square feet — 110 square feet short of the state threshold. If your plat says 0.25 acres exactly, the mandate does not reach you, though the law explicitly allows cities to permit detached ADUs on smaller lots, and some will. Before anything else, confirm the deeded square footage on your plat, your title policy, or the county parcel record. On this corridor, the lots that clear 11,000 square feet reliably are the older, larger-lot neighborhoods — often the same lots that already hold the detached garages and shops the conversion path was written for.

Converting an existing garage or shop

The conversion route is real, but a shop built as a shop is not a dwelling yet. Footings and framing often carry over; insulation, egress, heating, and dwelling-grade utility connections usually do not. Two questions come first on every conversion we look at: was the structure legally built and permitted, because the statute’s process covers legally constructed structures — and where is the sewer, because the city can lawfully deny a unit that required utilities cannot support. Utility answers come before drawings, not after.

The build sequence on a new detached ADU

A detached ADU is structurally a project we already know: engineered footings and a foundation, framing, roof, mechanical rough-ins, finishes. It is the same trade sequence as our custom homes in Huntsville and on Powder Mountain, scaled down — built with the same respect for footings we bring to the red-iron hangar work at the Brigham City airport. The sequence that keeps it clean:

1. Confirm the lot — deeded square footage, zone, recorded easements, and whether a development agreement rides on your subdivision.
2. Read the amended ordinance — setbacks, height, design consistency, and owner-occupancy are local calls.
3. Settle utilities early — connection points and capacity, in writing from the city wherever possible.
4. Design to the house — cities can require the ADU to match the primary dwelling’s design, and fighting that costs review cycles.
5. Permit and build — with every selection made before footings pour.

We are a Farmington-based Utah general contractor — B100 General Building license 11678454-5501, verifiable at dopl.utah.gov — and this corridor is home. If you are weighing a backyard cottage or a garage conversion, a free written estimate puts scope, price, and timeline on paper before any work begins.