A permitted use
On a qualifying lot, a detached ADU is allowed as of right. In a primarily residential zone the city cannot require a conditional use permit, which removes a discretionary hearing from the process.
Utah ADU law
SB 284 made backyard ADUs a permitted use.
Since October 1, 2026, larger Utah cities must allow a detached accessory dwelling unit (a separate small home in the backyard) on lots of 11,000 square feet or more. Here is who it affects, what cities can still require, and how to tell whether your lot qualifies.
The short version
- The rule: a covered city must allow one detached ADU on any lot of 11,000 square feet or larger that has a single-family home on it.
- The change: it is now a permitted use. In a primarily residential zone the city cannot require a conditional use permit.
- The catch: cities can still set size, height, setback, owner-occupancy and rental rules, so the details depend on your city.
- The source: Utah Code 10-21-304, enacted by S.B. 284 in the 2026 General Session.
What changed
From "ask your city" to "your city must say yes."
Before SB 284, whether you could build a separate backyard unit was up to each city, and many did not allow it. Internal ADUs, such as a basement apartment, were the common path. The new law requires covered cities to adopt a regulation that permits detached ADUs, and it limits what those regulations can do.
Capped parking
No more than one on-site space for a unit under 650 square feet, and no more than two for a unit of 650 square feet or larger.
A path for existing buildings
Cities must offer a process to convert a legally built accessory structure into an ADU, subject to setbacks and building, health and fire codes.
Codes still apply
Every detached ADU must meet the applicable building, health and fire codes. The law does not loosen safety requirements.
Who it affects
Homeowners in larger Utah cities.
Covered
- Cities of the first through fourth class
- Fifth-class cities of 5,000 or more people in a first-, second- or third-class county
- Owners of a lot of 11,000 square feet or more (about a quarter acre) with a single-family home where that use is permitted
- Owners who already have a legally built outbuilding they want to convert
Not required by this law
- Small towns and fifth-class cities under 5,000 people
- Lots smaller than 11,000 square feet (a city may still choose to allow them)
- Properties where a development agreement signed on or before May 6, 2026 restricts detached ADUs
- Private HOA or covenant rules, which are separate from city rules
Most Wasatch Front cities are covered, and many have already updated their codes. See where each city stands, including American Fork.
What your city can still require
The law sets a floor, not a template.
Within the limits above, each city writes its own standards. Under SB 284 a city may do all of the following, which is why two neighbors in different cities can get different answers.
Size and placement
- Apply structure size, dimension, height and maximum lot coverage limits
- Set setbacks, taking into account property lines, easements and neighboring structures
- Keep the unit out of the front yard and out of utility easements
- Prohibit an ADU larger than the main home
- Require a design consistent with the main home
Use and utilities
- Require the owner to live in the main home or the ADU
- Prohibit rentals shorter than 90 consecutive days
- Limit the lot to one accessory dwelling unit
- Require replacement parking when a detached garage is converted
- Deny a unit that lacks adequate utility access or where system capacity is insufficient
Does your lot qualify?
Five checks before you spend a dollar.
- Lot size. Look up your parcel. You need 11,000 square feet or more for the state mandate to apply.
- Your city. Confirm your city is covered and read its current detached ADU rules: footprint, height, setbacks, parking and owner occupancy.
- Utilities. Sewer, culinary water, electric and storm water all have to reach the new unit, and the system has to have capacity for it.
- Access. A factory-built unit arrives by truck and is set by crane. Side-yard width, overhead lines and the route to the backyard matter.
- HOA and covenants. Private rules are separate. Read yours first.
We will run these checks with you for free as part of a lot review.
Why modular fits
Small, code-built and set in a day.
Detached ADUs are small by design, which is where a factory-built home does its best work. These plans fit the sizes cities are writing into their codes.
Under 650 sq ft
Only one on-site parking space can be required. Several plans come in under that line.
Less time as a job site
Most of the build happens in the factory, so your yard and your neighbors deal with a short set day instead of months of framing.
Built to the residential code
Modules are built to the same International Residential Code your city applies to a house built on site, and they go through the same city review.
Questions
SB 284, answered.
Does SB 284 apply to my city?
It applies to what the bill calls a "specified municipality": any first-, second-, third- or fourth-class city, plus fifth-class cities with at least 5,000 residents that sit in a first-, second- or third-class county. That covers most Wasatch Front cities. Small towns and areas outside city limits are not covered by this section, so check with your city or county. American Fork is covered and has already adopted its rules.
My lot is smaller than 11,000 square feet. Can I still build one?
The law does not require your city to allow it, but it does not forbid it either. A city can choose to permit detached ADUs on smaller lots, and some already do. Ask your city planning office what applies to your parcel.
Can the city make me get a conditional use permit?
Not in a primarily residential zone. The law says a city cannot require a conditional use permit for a detached ADU there. You will still need a building permit and a plan review, and the project has to meet the city's size, height and setback rules.
Can I rent out a detached ADU?
Yes, with limits. A city may require rentals of at least 90 consecutive days, which rules out nightly and weekly short-term rentals. A city may also require the owner to live in either the main home or the ADU, so a long-term rental is usually fine, but a rental of both buildings to different tenants may not be.
How much parking does an ADU need?
A city cannot require more than one on-site space for a detached ADU under 650 square feet, or more than two for a unit of 650 square feet or larger. If you convert a detached garage, the city may require you to replace the parking that was in it.
Can I convert a shed, workshop or detached garage?
The law requires cities to have a process for converting a legally built accessory structure into a detached ADU. The structure still has to meet setback requirements and building, health and fire codes, which usually means real upgrades: insulation, egress, plumbing, electrical and a proper foundation. Often a purpose-built unit is the simpler path.
Does an HOA or neighborhood covenant still apply?
SB 284 governs city land use rules. It does not say that private covenants or HOA rules disappear, and some communities restrict ADUs on their own. Read your CC&Rs before you spend money on plans.
Is a modular ADU treated differently than a site-built one?
A modular ADU is built to the same residential code and goes through the same city review. The difference is that most of the building happens in a factory, so your yard is a construction site for a much shorter time. What matters for approval is the same: size, height, setbacks, utilities and parking.
Is this legal advice?
No. This page is a plain-language summary of the enrolled bill. Cities can add their own standards within what the law allows, and they can change them, so confirm the current rules with your city before you design or buy anything.
This page is general information, not legal advice. It summarizes the enrolled text of S.B. 284 (2026 General Session). Cities may adopt standards within what the law allows and may amend them, so confirm current rules with your city before you design or buy.
Let's see if your lot qualifies.
Send us your address and we will check lot size, your city's rules and the delivery route, then tell you straight whether a detached ADU makes sense.