ADU FAQ

An accessory dwelling unit is a second, smaller home on a single-family lot. Utah law defines it as a habitable living unit added to, created within, or detached from a single-family dwelling and contained on one lot or parcel. It is accessory to the main house, and several cities, including Millcreek, South Salt Lake and Sandy, bar selling it separately.

Under Utah law, an internal ADU is created within a primary dwelling and within its footprint at the time it is created, for long-term rental of 30 consecutive days or longer. A detached ADU is a separate structure on the same lot. The two fall under different state laws, and cities treat them differently on size, parking and approvals.

Largely, yes. In areas zoned primarily for residential use, Utah law makes an internal ADU a permitted use and limits what a city can require. A city may still prohibit one on a lot of 6,000 square feet or less, where the home has a failing septic tank, or in a limited share of its residential zones, and may add rules such as one extra parking space.

Since October 1, 2026, Utah Code 10-21-304 requires specified municipalities to permit a detached ADU on lots of 11,000 square feet or larger with a single-family home that is a permitted use. Cities may allow them on smaller lots and still regulate size, height, setbacks and coverage. Before that date, detached ADU rules are set city by city.

Usually one. Millcreek, Murray, Sandy, Cottonwood Heights, Salt Lake City and unincorporated Salt Lake County each allow a single ADU. South Salt Lake is the exception: a lot may have one internal and one external ADU.

In every city covered here, an owner (or in some cities a close relative) must live in the main house or the ADU, with limited exceptions. The requirement is usually documented in a recorded affidavit, notice or covenant, and some cities require a new approval after a sale.

In most of Salt Lake County, no. Salt Lake City, Murray, South Salt Lake, Cottonwood Heights and unincorporated Salt Lake County prohibit it, Holladay requires rentals of at least 30 consecutive days, and Millcreek and Sandy prohibit it for detached ADUs. Sandy lets an attached ADU alternate between short-term and long-term rental with approvals for both. Millcreek's rule for internal and attached ADUs is unresolved, so confirm with the city.

Utah law says an HOA rule may not prohibit an internal ADU as the state defines it, and an association may not restrict renting a code-compliant one. Whether that reaches CC&Rs is not settled in the statute text, and no statute protects detached ADUs from HOA restrictions. For a CC&R question, consult an attorney.

Usually not. Millcreek, Murray, South Salt Lake, Holladay, Sandy and Cottonwood Heights prohibit separate meters for an ADU, and state law lets cities prohibit them for internal ADUs. Unincorporated Salt Lake County allows a detached ADU to be separately metered if the owner is billed for both.

Most cities require one additional off-street space. Cottonwood Heights requires two for a detached ADU, and Sandy requires two for a detached unit of 650 square feet or more. Salt Lake City waives its one-stall requirement near transit stops and city bike lanes.

Utah adopts the 2021 International Residential Code with state amendments, including several written for ADUs inside an existing owner-occupied home. They cover separation between the units, egress, smoke and carbon monoxide alarms, return air and electrical disconnects.

Usually a planning or zoning approval for the ADU, a building permit, inspections and, if you rent it, a rental license. The order and names differ by city. Millcreek, South Salt Lake and Murray all require the planning step before the building permit.

No city covered here publishes a total timeline. Some publish targets for single steps, such as a first building review target of 14 business days in Salt Lake City. The completeness of the application and the number of review rounds make the biggest difference.

Utah law bars impact fees for an internal ADU built within an existing primary dwelling. There is no matching state exemption for detached ADUs, and most cities have not published how their impact fees apply to them. Ask the city and each utility provider before budgeting.

No current state statute creating an ADU loan or grant program was found. Salt Lake City's Redevelopment Agency runs the Backyard Keys ADU loan program for eligible owners west of I-15, accepting applications on a rolling basis as funding becomes available.

It depends on the type, size, foundation, utility runs, site access, finishes, engineering and fees, which is why we do not publish a single number. A basement conversion and a new detached cottage have very different cost drivers. Our cost guides explain each one.