Utah ADU Laws

Utah's ADU rules work in two layers. The state sets what cities and counties must allow and lists what they may restrict. Each city then writes its own ordinance inside those limits. This page covers the state layer as it reads on our review date. For how a specific city applies it, see our pages for Millcreek and the cities listed on the Salt Lake County page.

Key definitions

• Accessory dwelling unit: "a habitable living unit added to, created within, or detached from a single-family dwelling and contained on one lot or parcel."
• Internal ADU: created within a primary dwelling, within its footprint at the time it is created, and for the purpose of offering a long-term rental of 30 consecutive days or longer.
• Primary dwelling: a detached single-family dwelling occupied as the primary residence of the owner of record. It includes a garage that is habitable space and connected by a common wall.
• Detached ADU: an ADU not attached to or within a primary detached single-family dwelling, on the same lot or parcel.

Internal ADUs: what cities must allow

Under 10-21-303, in any area zoned primarily for residential use, an internal ADU is a permitted use. A city may not set restrictions for one internal ADU within a primary dwelling beyond the list below, including rules on the unit's size relative to the house, total lot size, street frontage or internal connectivity. Architectural rules must be consistent with those for single-family homes, including in historic districts. The unit must meet building, health and fire codes. See internal ADUs and basement ADUs.

Internal ADUs: what cities may restrict

A city may choose to:

• prohibit a separate utility meter;
• require that the house still look like a single-family dwelling;
• require one additional on-site parking space, unless the city already requires four off-street spaces, and require replacement of garage or carport parking lost to a conversion;
• prohibit an internal ADU in a mobile home, or where the home is served by a failing septic tank;
• require a permit or license to rent the unit;
• prohibit internal ADUs on lots of 6,000 square feet or less;
• prohibit internal ADUs in zoning districts covering 25 percent or less of the city's residential area (67 percent where a large university campus is located), with limits;
• prohibit renting the unit for less than 30 consecutive days;
• prohibit renting it if the home is not the owner's primary residence;
• record a notice with the county recorder, and hold a lien for violations.

Before a lien, the city must give a cure period of at least 14 days for a short-term rental violation or 30 days for others, and the lien is capped at $100 per day after that. Counties follow nearly identical rules under 17-80-303, with the area cap based on unincorporated residential land.

Detached ADUs: the law in effect since October 1, 2026

S.B. 284, passed in the 2026 General Session and signed March 18, 2026, creates Utah Code 10-21-304. It took effect October 1, 2026.

Who it covers. It applies to a "specified municipality": a city of the first, second, third or fourth class, or a fifth class city of 5,000 or more people located in a first, second or third class county. Towns are not included, and we found no county counterpart, so unincorporated areas are not covered. Check your city's classification before relying on it.

What it requires. A specified municipality must adopt a land use regulation permitting a detached ADU on any lot of 11,000 square feet or larger that contains a single-family dwelling, where the dwelling is a permitted use. Cities may also allow them on smaller lots. The regulation must require building, health and fire code compliance and include a process to convert a legally built accessory structure to a detached ADU.

What cities may not do. Require a conditional use permit for a detached ADU in a primarily residential zone; require more than two on-site parking spaces for a unit of 650 square feet or larger, or more than one for a smaller unit; or impose design standards that conflict with 10-20-618.

What cities may still do. Regulate structure size, dimension, height, maximum lot coverage and setbacks; require design consistent with the house; prohibit a detached ADU larger than the house, in a recorded easement or in a front yard; prohibit rentals under 90 consecutive days; require the owner to live in the house or the ADU; require replacement of parking lost in a garage conversion; allow only one ADU per lot; and prohibit a unit without adequate utility access or capacity.

The section also lists what it does not supersede, including rules for detached accessory buildings that are not ADUs and restrictions in development agreements signed on or before May 6, 2026. Cities are responding in their own ordinances: Sandy, for example, adopted new detached ADU rules on September 15, 2026. See detached ADUs and detached vs internal ADUs.

Impact fees

No political subdivision or private entity may impose an impact fee on building an internal ADU within an existing primary dwelling (11-36a-202). There is no matching exemption for detached ADUs. The moderate income housing plan statute lists "eliminate impact fees for any accessory dwelling unit that is not an internal accessory dwelling unit" as one strategy a city may choose, alongside creating or reducing regulations for ADUs. Utility district connection and capacity charges are set by each provider.

Short-term rentals

State law defines a short-term rental as occupancy for fewer than 30 consecutive days. It does not ban ADU short-term rentals itself: it lets cities prohibit internal ADU rentals under 30 consecutive days, and, under 10-21-304, detached ADU rentals under 90 consecutive days. Cities generally cannot punish someone solely for listing a short-term rental, but that protection does not apply to an internal ADU for which the city has recorded a notice. See ADU short-term rental rules.

HOAs and ADUs

Under 57-8a-218(16), an HOA rule may not prohibit an owner from building an internal ADU within their lot, unless it would violate a land use ordinance or a building, health or fire code. Under 57-8a-209(10), an association may not restrict renting a code-compliant internal ADU. Both apply regardless of when the association was created.

There is a caveat. The statute limits a "rule", and the Act defines a rule as excluding items set forth in a declaration. The Utah Department of Commerce's HOA office reads the protection as covering CC&Rs as well. That is agency guidance, not settled statute, so review your CC&Rs. The same office says HOAs can prohibit detached ADUs. See ADU HOA rules.

Building code

Utah Code 15A-2-103 adopts the 2021 International Residential Code, the 2024 editions of the building, existing building, energy, plumbing and mechanical codes, and the 2023 National Electrical Code. A version effective January 1, 2027 keeps those editions and adopts the 2024 International Wildland-Urban Interface Code. Utah amends the IRC for ADUs in several places:

• a definition of an ADU as a habitable unit within the existing footprint of an owner-occupied single-family home (R202);
• an exception to R302.3 for ADUs separated by walls or floors protected by at least 1/2-inch gypsum board on each side;
• ADU additions to R310.7, R314.2.2 and R315.2.2;
• return air between an ADU and another dwelling unit is not prohibited (M1602.2);
• an ADU occupant need not have access to the disconnect serving their unit (E3601.6.2).

The state rule that stops cities from requiring egress changes to bedrooms that met code when finished does not apply to an internal ADU (10-20-606). What these amendments mean for a given house depends on the underlying IRC sections; see ADU building code.

Contractors and financing

A contractor's license number must appear on permit applications, contracts, agreements and bids when a license is required (58-55-304). We found no current state ADU loan or grant program in Utah Code; see how to finance an ADU.

What this means for your project

State law tells you what your city cannot forbid and what it may add. The city ordinance, and sometimes an HOA's documents, decide the rest. The ADU permit process walks through the steps, and See What Your Property Can Support is where we apply both layers to your lot.

Questions about Utah ADU laws