Utah ADU Builder
Utah law · reviewed September 24, 2026
Utah ADU law, explained
Utah has two ADU laws that matter to homeowners: the internal-ADU law (2021) and S.B. 284's detached-ADU rule, which takes effect October 1, 2026. Cities still set many details. This is planning information, not legal advice.
The short answer
- Internal ADUs (a basement or other unit inside the home) are a permitted use in owner-occupied single-family homes in residential zones under Utah’s 2021 internal-ADU law. Cities may still require owner occupancy, a permit and parking, and may prohibit them on lots of 6,000 sq ft or less.
- Detached ADUs: beginning October 1, 2026, every “specified municipality” must permit a detached ADU on any lot of 11,000 sq ft or more that contains a permitted single-family home (Utah Code 10-21-304, enacted by S.B. 284).
- Cities may allow detached ADUs on smaller lots, and many already do. 84 of the 102 cities we cover are specified municipalities.
- HOA covenants, plat notes and some development agreements signed on or before May 6, 2026 can still restrict ADUs.
Which cities must follow S.B. 284?
A “specified municipality” is a city of the first, second, third or fourth class, or a fifth-class city with 5,000 or more residents in a county of the first, second or third class. In practice that means cities of roughly 10,000+ people, plus 5,000+ cities in larger counties. Towns and small cities are not required to follow the detached-ADU rule, though they may allow detached ADUs on their own.
Each city page shows whether the city is covered, and the rules-by-city table compares all of them.
What the detached-ADU law requires cities to do
A specified municipality’s detached-ADU rules must:
- Permit a detached ADU on a lot of 11,000 sq ft or more with a single-family home that is a permitted use there.
- Require the unit to meet building, health and fire codes.
- Include a process to convert a legally built accessory structure (such as a detached garage) into a detached ADU, subject to setbacks and codes.
What cities may not require
| Rule | Limit under Utah Code 10-21-304(3) |
|---|---|
| Conditional use permit | Not allowed for a detached ADU in a primarily residential zone. |
| Parking, unit 650 sq ft or larger | No more than 2 on-site spaces assigned to the ADU. |
| Parking, unit under 650 sq ft | No more than 1 on-site space assigned to the ADU. |
| Design standards | May not conflict with Utah Code 10-20-618. |
What cities may still require
- Limits on size, dimensions, height and lot coverage, and setbacks (which can consider windows, massing and nearby structures).
- A design consistent with the main home.
- That the ADU be no larger than the main home, not in a utility or recorded easement, and not in the front yard.
- A minimum rental term of up to 90 consecutive days (no nightly rentals).
- That the owner live in the main home or the ADU.
- Replacement of required parking when a garage is converted.
- Only one ADU per lot.
- Denial when required utilities (sewer, water, power, storm water) are unavailable or lack capacity.
Cities that adopted new ADU ordinances in 2026
Recorded council votes, linked to the public meeting record on OpenUtah.
| City | Date | Action |
|---|---|---|
| Kaysville | 2026-09-17 | City Council approved an ordinance amending 17-31-3 to regulate internal and detached ADUs to comply with SB 284, with changes discussed; vote from transcript. Record |
| South Jordan | 2026-09-15 | City Council approved Ordinance 2026-24 amending definitions, zones and the ADU Floating Zone to conform with state law; vote from transcript. Record |
| Saratoga Springs | 2026-09-15 | City Council approved Ordinance 26-42 amending Chapter 19.20 to add detached ADU rules (11,000 sq ft min lot) to comply with state law; vote from transcript. Record |
| St. George | 2026-08-20 | City Council approved Ordinance 2026-068 allowing one attached plus one detached ADU on lots of 11,000+ sq ft to comply with SB 284; vote from transcript. Record |
| Park City | 2026-08-13 | Approved Ord. 2026-19 amending the LMC (condo plat review to staff, S.B. 284 procedural alignment for planning commissioners, appeals and business licenses, TIS/TDM, historic-district fences); did not change ADU/accessory apartment rules Record |
| Nibley | 2026-08-06 | Approved Ord. 26-09 amending ADU standards (lot size, impact fees, conversion of existing accessory buildings) as recommended by the Planning Commission (4-0). Record |
| Lehi | 2026-07-14 | Approved Ordinance 2026-31 amending Chapter 26 detached ADU rules for SB 284: 11,000 sq ft minimum lot, 1 or 2 parking stalls by size, size cap tied to the main home, 6 ft from the house, and no CUP for conversions (5-0). Record |
| Tremonton | 2026-07-07 | Adopted Ord. 26-10 amending Chapters 1.03 and 1.07: defined small accessory structures, fixed accessory/main building height discrepancy, changed side setbacks for ADUs, allowed single-family homes in RM-8/RM-16 (5-0 roll call) Record |
| Providence | 2026-06-17 | Adopted Ordinance 10-2026, IADU/ADU incentive extension amendment (city ordinance page lists adoption 06/17/2026; codifier history shows 6/29/2026). Vote tally not published in text form. Record |
| Herriman | 2026-05-27 | City Council approved Ordinance 2026-11 permitting detached ADUs (10,000 sq ft minimum lot, one ADU per lot); vote taken from meeting transcript. Record |
| Cottonwood Heights | 2026-05-20 | Approved Ordinance 465 amending 19.75.050 and 19.76.030 regarding separate utility meters for ADUs and guest houses (5-0). Record |
| West Jordan | 2026-03-24 | Approved Ordinance 26-18 amending City Code 13-5B-8 (ADUs): state 'detached ADU' terminology, septic prohibition, and rules for a second utility meter on detached ADUs (6-0). Record |
| West Jordan | 2026-03-24 | City Council approved Ordinance 26-18 amending City Code 13-5B-8 (Accessory Dwelling Units); video shows the 6-0 vote on March 24, 2026. Record |
| South Jordan | 2026-02-17 | Motion made to approve Ordinance 2026-04 amending ADU Floating Zone prohibitions; the record does not state the result. Record |
| South Jordan | 2026-02-03 | City Council approved Ordinance 2026-03 after striking the section on prohibitions in the ADU Floating Zone. Record |
Internal ADUs: the 2021 law
Utah’s internal-ADU law (H.B. 82, 2021, now Utah Code 10-21-303) made one internal ADU a permitted use in an owner-occupied detached single-family home in a residential zone. Cities can still require a permit, owner occupancy and one additional parking space, and may prohibit internal ADUs on lots of 6,000 sq ft or less. Local details, such as whether a recorded owner-occupancy notice or business license is required, are on each city page.
Check your lot size
Check your parcel against these rules
Map the address, open your city page, then request a free review if the path looks real.
Sources
- Utah S.B. 284 (2026), enrolled copy — Utah State Legislature
- S.B. 284 bill page — Utah State Legislature
- Utah Code 10-21-304, Detached accessory dwelling units — Utah State Legislature
- Utah Code 10-21-303 (internal ADUs) — Utah State Legislature
- H.B. 82 (2021) bill page — Utah State Legislature
Reviewed 2026-09-24. Not legal advice; confirm the current code and your city’s ordinance before you apply.