ADU Guide · Verified 2026
Building an ADU in Utah
Utah guarantees ADUs statewide, but only INTERNAL ones. Under HB 82 (2021, Utah Code § 10-9a-530), every city and county must allow at least one internal accessory dwelling unit — a unit built within an existing single-family home — as a permitted use in residential zones. Detached backyard units are NOT covered by the state guarantee and remain entirely up to local rules. Cities may still require owner-occupancy, one extra parking space, and a rental license, and may prohibit internal ADUs in up to a quarter of their residential land.
Quick Facts
Statewide floors set by Utah Code § 10-9a-530 (municipal) / § 17-27a-526 (county), created by HB 82 (2021). Your city may be more generous but cannot go below them.
The Three Types of ADU
What you can build by right
HB 82 requires every Utah municipality and county to treat one internal accessory dwelling unit as a permitted use in areas zoned primarily for residential use (Utah Code § 10-9a-530). "Internal" is the key word: the unit must be created within the existing footprint of a detached single-family home — think a basement apartment or a converted upstairs. A city cannot establish restrictions or requirements that block the construction or use of that one internal ADU, beyond the specific conditions the statute allows. This is a narrower guarantee than California or Washington, but within its lane it is a genuine by-right protection.
The detached-unit gap
The most important thing to understand about Utah is what the law does NOT cover. The statewide permitted-use protection applies only to internal units. A detached backyard cottage is not guaranteed — a city can allow it, encourage it, or prohibit it entirely, and many treat detached ADUs very differently from internal ones. If you want a standalone unit, do not assume the state law helps you; the local ordinance is the whole answer, and you should confirm with your city planning department before designing anything detached.
Owner-occupancy is often still required
This is the point homeowners most often get wrong. HB 82 removed the idea that the state mandates owner-occupancy, but it did NOT forbid cities from keeping an owner-occupancy condition — and many Utah cities (Kaysville and Logan among them) still require the owner to live in either the main home or the internal ADU. The statute even defines the primary dwelling as one occupied as the owner's primary residence. An investor hoping to rent both units should verify whether the specific city still imposes owner-occupancy before counting on it.
Long-term rental only
The statute defines an internal ADU as a unit offered for a long-term rental of 30 consecutive days or longer. That definition effectively excludes short-term or nightly rentals from the protection — a city may prohibit using an internal ADU as a short-term rental, and may record a notice against the property's title if it is used in violation. If your plan is an Airbnb-style rental, the internal-ADU guarantee does not cover it.
What cities can still require
HB 82 set a baseline and then listed the conditions a municipality may attach. Cities may require one additional off-street parking space for the internal ADU (and require replacing garage parking that is converted), require a rental license or basic registration, apply building, health and safety codes (egress, fire separation, inspection), and cap occupancy. Some cities set a height limit of 20 feet or the height of the primary dwelling, whichever is lower, on any associated work. These are real conditions, but they cannot add up to a de-facto prohibition of the one guaranteed internal unit.
The 25% local opt-out
A city or county may prohibit the creation of internal ADUs in zoning districts covering up to roughly 25% of the area zoned primarily for single-family residential use (a higher share applies in some university-town carve-outs). So even the internal-ADU guarantee has a geographic exception: your specific parcel could fall in an opted-out district. This is why checking the local zoning map matters even for an internal unit that the state otherwise protects.
HOAs cannot ban internal ADUs
One clear win: HB 82 makes it illegal for private homeowners associations and developments with CC&Rs to prohibit internal ADUs. So unlike in several other states where the state law leaves HOA covenants untouched, in Utah an HOA cannot use its CC&Rs to block an internal unit. HOA design and performance standards may still apply in reasonable ways, but an outright ban on the internal ADU is not enforceable.
What people get wrong
Three misconceptions. First, that Utah legalized backyard cottages statewide — it did not; only internal units are guaranteed, and detached units are purely local. Second, that owner-occupancy is gone — it is not; cities may and often do still require it. Third, that the unit can be an Airbnb — the protection is defined around long-term (30+ day) rental, and short-term use can be prohibited. Read the guarantee narrowly and confirm the rest with your city.
From Idea to Move-In: The Timeline
Who Administers It
Check Your County
Select your county for local rules, fees, and your building department's contact details:
Building It Yourself? Here's What You'll Need
Planning an ADU? Tools homeowners use in the design and layout phase:
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Check Your Local Rules
Your city may allow more than the state floor
State law sets the minimum; many Utah cities are more generous. Confirm specifics with your local planning department.
Find your county building department →Not sure if your project needs a building permit, a zoning approval, or both? See our guide to building permits vs. zoning approval.
Official Sources
ADU law changes frequently and local ordinances add detail. This guide is general information, not legal advice — always confirm with your local building department. Reviewed by the StateDataIndex Editorial Team · Updated August 2026.