In plain words

Utah has a narrower statewide ADU law than some states. An ADU (accessory dwelling unit) is a smaller second home on the same lot as a house.

Since 2021, every Utah city, town and county must allow an internal ADU in areas zoned mainly for homes. An internal ADU sits inside the footprint of the main house, like a basement apartment. It is a "permitted use," so it needs no special hearing. That is often called "by right." It applies only when the owner lives there. Local governments can still ban rentals shorter than 30 days and require one extra parking space. They can also exclude lots of 6,000 square feet or less. And they can keep internal ADUs out of up to a quarter of their residential land. Homeowners associations (HOAs) cannot ban internal ADUs that meet local codes. No impact fee, a one-time charge for public services, may be charged for an internal ADU built inside an existing home.

Since October 1, 2026, larger cities must also allow a detached ADU. That is a separate building, like a backyard cottage. The rule covers cities of 10,000 or more people and some cities of 5,000 or more. The lot must be at least 11,000 square feet and already have a single-family house. Cities cannot require a conditional use permit in residential zones. That is a special, case-by-case approval. They may still require the owner to live on site. They may also ban rentals under 90 days, require one or two parking spaces, and allow only one ADU per lot. HOAs can still ban detached ADUs.

On smaller lots, in smaller towns and in county areas outside cities and towns, detached ADUs depend on local zoning. Zoning is the set of local rules about what can be built where.

The rules at a glance

State ADU lawYes
Where the state rule appliesInternal ADUs: every municipality and county, in areas zoned primarily for residential use. Detached ADUs (from 2026-10-01): 'specified municipalities' only, meaning cities of the first through fourth class (10,000+ people) and fifth-class cities of 5,000+ people in first-, second- or third-class counties; counties and smaller towns are not covered.
Approved without a hearing?Partly. Some ADUs or some places get staff approval; others can still need a hearing.
Kinds of ADU the state protectsinternal, detached
ADUs per lot1 internal ADU protected statewide; 1 detached ADU on qualifying lots in specified municipalities; cities may cap a lot at one ADU in total
Owner living on siteTowns may require the owner to live on the property.
ParkingInternal ADU: a city or county may require one extra on-site space (not if its code already requires four off-street spaces for the house) and may require replacing garage or carport spaces lost to a conversion. Detached ADU: no more than one on-site space for a unit under 650 sq ft and no more than two for 650 sq ft or larger; replacement of garage spaces lost to a conversion may be required.
SizeInternal ADU: no limit on its size relative to the house, but by definition it must fit inside the house's existing footprint. Detached ADU: cities may apply their general rules on structure size, dimensions, height and lot coverage, and may bar a detached ADU larger than the main house.
Lot size and setbacksInternal ADU: no total lot size or street frontage requirement, except a city or county may ban internal ADUs on lots of 6,000 sq ft or less, on homes with failing septic systems, and in mobile homes. Detached ADU: must be allowed on lots of 11,000 sq ft or more (cities may allow smaller); cities may apply setbacks that consider property lines, nearby structures, easements, windows and massing, and may bar units in front yards, in utility or other recorded easements, or where sewer, water, power or storm-water service or capacity is inadequate. Owners of a legally built accessory building must have a path to convert it, subject to setbacks and codes.
FeesCities, counties and other local entities may not charge an impact fee for building an internal ADU inside an existing primary dwelling (Utah Code 11-36a-202(2)(a)(vi)). The state sets no fee rule for detached ADUs.
Short-term rentalsInternal ADU: local governments may ban rentals of less than 30 consecutive days and may require a rental permit or license. Detached ADU: cities may ban rentals of less than 90 consecutive days.
Can towns opt out?No

What to do next

  1. Look up your lot size on your county's parcel map and confirm whether your city has 10,000+ people (or 5,000+ in a more populous county), which decides whether the detached ADU rule applies.
  2. Read your city's or county's internal and detached ADU ordinances; many cities updated theirs to meet the October 1, 2026 deadline.
  3. For an internal ADU, check that your lot is over 6,000 square feet, your zone is not one of the excluded districts, and you can provide any required extra parking space.
  4. For a detached ADU, confirm setbacks, height and lot coverage limits and ask your utilities whether sewer, water and power have capacity for another unit.
  5. Check your HOA's CC&Rs: HOAs cannot block internal ADUs that meet codes, but they can still prohibit detached ones.
  6. Ask whether your city requires a rental license or records a notice on your title for an ADU, and plan for the owner-occupancy rule if you intend to rent.

Grants, loans and tax breaks

  • Low-income ADU Loan Guarantee Pilot Program (Utah Admin. Code R982-502): Created by H.B. 82 (2021) as a two-year pilot in which the state housing division could guarantee 15-year fixed-rate lender loans to homeowners who build an ADU and rent it to households under 80% of area median income. The rule took effect February 22, 2022; we could not confirm the program is still taking applications, so treat it as possibly ended and check with the Division of Housing and Community Development. Program page

What your town still decides

The state law has built-in carve-outs rather than an opt-out. For internal ADUs, a city or county may exclude zoning districts covering up to 25% of its residential land (up to 67% in a city with a main university campus of 10,000+ students), but it cannot block internal ADUs in subdivisions with final plat approval on or after October 1, 2021. The internal ADU protection only applies to a detached single-family home that is the owner's primary residence, and local governments may bar renting an internal ADU in a home the owner does not live in; they may also place a lien (up to $100 a day) for uncured violations after notice and a chance to object. For detached ADUs, cities had until October 1, 2026 to update their codes; the rule does not override development agreements signed on or before May 6, 2026, it expressly leaves in place other local ADU rules 'not prohibited by law', and cities may still require owner residence and design consistent with the house. Detached ADUs on smaller lots, in towns under the population thresholds, and in unincorporated county areas remain a local choice. HOAs may still prohibit detached ADUs, according to the Utah Department of Commerce HOA office.

Examples of local rules

  • Salt Lake County (unincorporated areas): Adopted an ordinance on June 4, 2024 to loosen ADU limits. Internal ADUs need a lot of at least 6,000 sq ft; detached ADUs need 7,000 sq ft (6,000 in the PC zone). Internal ADUs follow the house's setbacks; detached ADUs must sit 10 feet from the rear lot line and 6 feet from the house, with side setbacks set by zone. One on-site parking space is required for the ADU, detached units may be up to 20 feet tall or match the house depending on setbacks, and either the house or the ADU must be owner-occupied. Source
  • Salt Lake City: Publishes an ADU handbook and a set of ADU plans pre-approved by building code staff (a site review is still required for the permit). Westside homeowners can apply for Backyard Keys construction loans through the city's Community Reinvestment Agency, reported at up to $200,000 at a 3% fixed rate, with partial forgiveness for rent-restricted units. Source
  • Lehi: Already allowed detached ADUs on lots of 14,520+ sq ft before S.B. 284. Its updated policy requires 6-foot setbacks from the main home and owner occupancy of one of the two units; city staff estimated eligible lots could rise by up to about 20%. (News report.) Source
  • Orem: Previously did not allow detached ADUs; as of July 2026 it was drafting rules to comply with S.B. 284 that bar front-yard placement and short-term rentals. Check the city for the adopted version. (News report.) Source

What we’re still confirming

  • Whether the state's 2021 low-income ADU loan guarantee pilot is still running isn't clear.
  • News reports say cities can't cap the size of detached ADUs, but the statute lets cities apply general size, height and lot-coverage rules and limit an ADU to the size of the house.

Laws, bills and citations

The laws behind this (2)
  • Local Land and Water Modifications (detached ADU mandate) (S.B. 284 (2026 General Session), Laws of Utah 2026 ch. 166; Utah Code 10-21-304, signed March 18, 2026, in effect October 1, 2026). A broad land-use bill that, among other things, requires larger cities ('specified municipalities') to adopt rules permitting a detached ADU on any lot of 11,000 square feet or more that has a single-family home where the home is a permitted use. Cities cannot require a conditional use permit in primarily residential zones and can require at most one parking space for units under 650 sq ft or two for larger units, but may require owner residence, ban rentals under 90 days, limit a lot to one ADU, and refuse a unit when utility service or capacity is inadequate. The section does not override development agreements signed by May 6, 2026. Read it
  • Internal accessory dwelling units (H.B. 82 (2021 General Session), Single-Family Housing Modifications; now Utah Code 10-21-303 (cities, renumbered by Laws of Utah 2025, 1st Special Session ch. 15) and 17-80-303 (counties, renumbered by 1st Special Session ch. 14); HOA provisions at Utah Code 57-8a-209(10) and 57-8a-218(16), signed March 16, 2021, in effect October 1, 2021). Makes one internal ADU (a unit inside the footprint of an owner-occupied detached house) a permitted use in every area zoned primarily for residential use, in all cities, towns and counties, and bars most local restrictions on it. Local governments keep a list of allowed limits, such as an extra parking space, a 6,000 sq ft minimum lot, a ban on rentals under 30 days, and excluding internal ADUs from up to 25% of their residential land. HOAs cannot ban internal ADUs or their rental if they meet local codes. Read it
Proposed and failed bills (3). None of these is law.
  • H.B. 477 (2026): died as of October 3, 2026. Land Use Regulation Revisions, which included a requirement that larger cities allow detached ADUs as a permitted use in certain zones. It was filed as not passed on March 6, 2026; the detached ADU mandate became law through S.B. 284 instead. Bill page
  • H.B. 88 (2025): died as of October 3, 2026. Housing Policy Amendments would have made one ADU, internal or external, a permitted use on lots with a detached single-family home in residential zones of urban cities, and barred those cities from banning modular homes. It stalled in committee amid city opposition and was filed as not passed on March 7, 2025. Bill page
  • H.B. 398 (2025): died as of October 3, 2026. Auxiliary Housing Amendments would have changed the owner-occupancy rules tied to internal ADUs; a substitute version also set deadlines for cities and counties to process internal ADU applications. It was filed as not passed on March 7, 2025. Bill page

Sources

  1. S.B. 284 (2026 General Session), Laws of Utah 2026 ch. 166; Utah Code 10-21-304 · official source
  2. H.B. 82 (2021 General Session), Single-Family Housing Modifications; now Utah Code 10-21-303 (cities, renumbered by Laws of Utah 2025, 1st Special Session ch. 15) and 17-80-303 (counties, renumbered by 1st Special Session ch. 14); HOA provisions at Utah Code 57-8a-209(10) and 57-8a-218(16) · official source
  3. Utah Code 10-21-304 Detached accessory dwelling units (effective 10/1/2026) · official source · checked 2026-10-03
  4. Utah Code 10-21-303 Internal accessory dwelling units (municipalities) · official source · checked 2026-10-03
  5. Utah Code 17-80-303 Internal accessory dwelling units (counties) · official source · checked 2026-10-03
  6. Utah Code 10-21-101 Definitions, including 'specified municipality' and 'primary dwelling' (effective 7/1/2026) · official source · checked 2026-10-03
  7. Utah Code 10-2-301 Classification of municipalities according to population · official source · checked 2026-10-03
  8. Utah Code 11-36a-202 Prohibitions on impact fees, including internal ADUs · official source · checked 2026-10-03
  9. S.B. 284 enrolled text, including Section 26 (10-21-304) and Section 52 (effective dates) · official source · checked 2026-10-03
  10. H.B. 477 Land Use Regulation Revisions, 2026 General Session · official source · checked 2026-10-03
  11. H.B. 88 Housing Policy Amendments, 2025 General Session · official source · checked 2026-10-03
  12. H.B. 398 Auxiliary Housing Amendments, 2025 General Session · official source · checked 2026-10-03
  13. Accessory Dwelling Units, HOA guidance (Utah Department of Commerce, Office of the HOA Ombudsman) · official source · checked 2026-10-03
  14. Rule R982-502 Low-income ADU Loan Guarantee Pilot Program (Utah Office of Administrative Rules) · official source · checked 2026-10-03
  15. Accessory Dwelling Units (Salt Lake County Office of Regional Development) · official source · checked 2026-10-03
  16. Accessory Dwelling Unit Standard Plans (Salt Lake City Building Services) · official source · checked 2026-10-03
  17. Backyard Keys ADU Loan Program (Salt Lake City Community Reinvestment Agency) · official source · checked 2026-10-03
  18. Utah County cities prepare for statewide detached ADU changes (Daily Herald, July 15, 2026) · checked 2026-10-03
  19. Utah lawmakers say no to 'preemption,' halt 2 housing bills (Utah News Dispatch, Feb 12, 2025) · checked 2026-10-03

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.