Utah SB 284: Statewide Detached ADUs Explained (2026)

Utah's S.B. 284 quietly did something big for backyard housing: on qualifying single-family lots, a detached ADU is now supposed to be a permitted use, no conditional-use hearing required. But there are two catches most summaries skip. First, the mandate only reaches lots that are 11,000 square feet or larger in a specific set of cities, not "every city with 5,000 people." Second, the detached-ADU rules were signed in March 2026 but do not become operative until October 1, 2026, and your city still has to update its ordinance after that. Here is what SB 284 actually changed, what it left to your city, and what to do about it.

Bottom Line

Utah S.B. 284 (2026 General Session), officially titled "Local Land and Water Modifications," is an omnibus land-use and water bill. Buried inside it is the state's first statewide mandate for detached accessory dwelling units, enacted as a brand-new statute, Utah Code § 10-21-304 ("Detached accessory dwelling units") [1]. Governor Cox signed the bill on March 18, 2026 [3]. The bill's general effective date is May 6, 2026, but § 10-21-304 carries a special, delayed effective date of October 1, 2026 [1].

The core rule is precise. A "specified municipality" must adopt a land-use regulation permitting a detached ADU as a permitted use on any lot that is 11,000 square feet or larger and that contains a permitted single-family dwelling [1]. In those cities, that means no conditional-use permit in a primarily residential zone, and capped parking: no more than two on-site spaces for an ADU that is 650 square feet or larger, and no more than one space for an ADU smaller than 650 square feet [1].

Three things to keep straight before you get excited. The mandate does not reach every Utah city, only "specified municipalities" as narrowly defined (below). It does not reach lots smaller than 11,000 square feet (your city may allow ADUs on smaller lots, but SB 284 does not force it) [1]. And it is not operative yet. As of this writing in July 2026, the detached-ADU rules are enacted but not in effect; they switch on October 1, 2026, after which cities bring local ordinances into compliance [1]. Anyone telling you detached ADUs are "already legal statewide in Utah" is wrong on the calendar.

Myth	Reality
"The mandate covers lots smaller than 11,000 sq ft (some say 10,000)."	No. The permitted-use mandate applies to lots that are 11,000 square feet or larger. Cities may extend it to smaller lots but are not required to. [1]
"SB 284 legalizes detached ADUs in every Utah city with 5,000+ residents."	No. It binds only a "specified municipality": a first-, second-, third-, or fourth-class city, or a fifth-class city of 5,000+ located in a first-, second-, or third-class county. [1]
"Detached ADUs are legal statewide in Utah right now."	No. § 10-21-304 was signed March 18, 2026 but is not operative until October 1, 2026, and each city must then update its ordinance. [1][3]
"SB 284 bans cities from requiring owner-occupancy."	No. Covered cities may still require the owner to live in either the primary dwelling or the ADU. [1]

What SB 284 Actually Does

Strip away the omnibus packaging and the ADU piece of SB 284 is a single new statute with a single job: make a detached ADU a by-right permitted use on larger single-family lots in Utah's more urban cities.

Here is the operative language. A specified municipality "shall adopt a land use regulation that permits a detached accessory dwelling unit on any lot or parcel that is 11,000 square feet or larger and contains a single-family dwelling, if the single-family dwelling is a permitted use on the lot or parcel" [1]. That is the whole mandate in one sentence. Two conditions have to be true at once: the lot is at least 11,000 square feet, and it already carries a single-family home (or could, as a permitted use).

"Permitted use" is the phrase that carries the weight. In land-use terms, a permitted use is allowed as of right, subject to objective standards; it does not go through a discretionary hearing where a planning commission can say no. That is the difference between a homeowner filling out a checklist and a homeowner spending months and thousands of dollars on a conditional-use process with an uncertain outcome. SB 284 pushes qualifying detached ADUs firmly into the first category [1].

The bill also forces two affirmative requirements into the local regulation. The ADU must comply with all applicable building, health, and fire codes, and the city must include a process for the owner of a legally constructed existing accessory structure to convert that structure into a detached ADU, subject to setback rules and the building/health/fire codes [1]. That conversion path matters: it gives owners of old detached garages, shops, and outbuildings a defined route to legalize a unit rather than build new.

What SB 284 does not do is equally important. It does not touch Utah's existing internal ADU law (more on that below). It does not preempt legitimate size, height, setback, or design rules. And it does not switch on immediately. The detached-ADU obligation is a floor that covered cities must meet by updating their codes once the statute becomes operative, not a self-executing right that homeowners can invoke the day the governor signs.

Who's Covered: the 11,000 Sq Ft Lot + "Specified Municipality" Test

This is where most of the online confusion lives, so read it carefully. SB 284's detached-ADU mandate only applies where both of two tests are met.

Test 1 — The lot. The lot or parcel must be 11,000 square feet or larger and contain a single-family dwelling that is a permitted use [1]. If your lot is 10,800 square feet, the mandate does not reach it. The statute is explicit that it "does not prohibit a municipality from adopting a land use regulation that permits a detached accessory dwelling unit on a lot or parcel that is smaller than 11,000 square feet" [1] — in other words, cities are free to go further and allow detached ADUs on smaller lots, but nothing in SB 284 requires them to. Do not assume a sub-11,000 sq ft lot is covered; check your local ordinance.

Test 2 — The city. The mandate binds only a "specified municipality," and the definition is narrower than the "any city over 5,000 people" shorthand that circulates online. Under the statute, a specified municipality means [1]:

a city of the first, second, third, or fourth class; or
a city of the fifth class with a population of 5,000 or more, if that city is located within a county of the first, second, or third class.

Utah classifies cities and counties by population under state law, so "class" is a legal size bucket, not a subjective label. The practical effect is that Utah's larger cities and mid-size cities along the Wasatch Front are squarely covered, while small fifth-class cities in rural, lower-class counties generally are not bound by the mandate, even if they happen to have a few thousand residents. That is why "every city with 5,000+ people" is wrong: a fifth-class city only gets pulled in when it clears 5,000 and sits inside a first-, second-, or third-class county [1].

If you are not certain which class your city and county fall into, that is the first question for your city planning department, because it decides whether SB 284 obligates your city at all. If your city is not a specified municipality, whether you can build a detached ADU is governed entirely by existing local code, and SB 284 changes nothing for you.

What Cities Can No Longer Require

Once § 10-21-304 is operative and applies to your lot and city, the local regulation may not do any of the following [1]:

Require a conditional use permit for the detached ADU if it is located in a primarily residential zone. This is the headline change. No discretionary hearing, no case-by-case approval gauntlet for a qualifying backyard unit.
Require more than two on-site parking spaces for a detached ADU that is 650 square feet or larger.
Require more than one on-site parking space for a detached ADU that is smaller than 650 square feet.
Impose design standards that conflict with Utah's separate design-review limitations for these units.

Those parking numbers are ceilings, not floors. A city can require fewer spaces (including zero, in transit-rich areas if it chooses), but it cannot demand more than the statutory cap tied to the 650-square-foot line [1]. For a small backyard cottage under 650 square feet, that means a single space is the most the city can ask for, which removes a common cost-and-space obstacle on tighter lots.

The conditional-use prohibition is the provision most likely to change real outcomes. Before SB 284, a homeowner in a covered city could face a conditional-use process where neighbors and a planning commission had discretion to deny a detached ADU on vague "compatibility" grounds. In a primarily residential zone, that discretionary veto is gone for qualifying units. The city can still enforce objective standards, but it cannot make the unit contingent on a hearing it might lose [1].

What Cities Can Still Require

SB 284 is not a deregulation free-for-all. The statute expressly preserves a long list of local powers. A covered city may still [1]:

Require the ADU to conform to structure size, dimension, height, and maximum lot-coverage regulations.
Require the ADU to meet setback requirements, which can account for proximity to property lines and other structures, easements, window orientation, and massing.
Require the ADU to be designed consistent with the primary single-family dwelling.
Cap the ADU's size so it is not larger than the primary dwelling on the same lot.
Prohibit front-yard placement of the detached ADU.
Prohibit rentals shorter than 90 consecutive days — in plain terms, ban nightly and short-term rental of the unit.
Require owner-occupancy: the city may require that the owner reside in either the primary single-family dwelling or the detached ADU on the lot.
Limit the lot to one ADU.
Require replacement parking on-site when a detached garage is converted, and prohibit an ADU that lacks adequate access to required utility services.

Two of these deserve emphasis because they are widely misunderstood. First, owner-occupancy is not banned. SB 284 explicitly lets cities keep an owner-occupancy requirement, satisfied by living in either unit [1]. If you were planning to buy a covered lot purely as a rental with both units tenant-occupied, you cannot assume that is allowed; it depends on your city's ordinance. Second, the 90-day minimum-rental option lets cities block short-term rental of the ADU without banning long-term rental. An investor counting on Airbnb-style income needs to check whether the local ordinance adopts that 90-day floor [1].

The takeaway: SB 284 removes the discretionary barriers (the conditional-use hearing, excessive parking) but leaves the objective zoning toolkit — size, height, setbacks, design, occupancy, rental duration — largely in city hands.

Timeline: Signed March 2026, Effective October 2026

The dates are the single most error-prone part of this bill, so here is the sequence in order [1][3]:

Date	What happens
March 18, 2026	Governor signs S.B. 284. [3]
May 6, 2026	The bill's general effective date. Most of the omnibus bill takes effect.
October 1, 2026	The detached-ADU section (§ 10-21-304) becomes operative under its special effective date.
After Oct 1, 2026	Covered cities bring local ordinances into compliance with the permitted-use mandate.

The reason this matters: SB 284 uses a special effective date for the ADU provisions specifically, delaying § 10-21-304 to October 1, 2026 even though the rest of the bill switched on May 6, 2026 [1]. So there is a window — roughly May through September 2026 — in which SB 284 is "law" but the detached-ADU mandate is not yet operative. During that window, no homeowner can force a city to grant a by-right detached ADU under this statute, and cities are not yet obligated to have compliant ordinances on the books.

Even after October 1, 2026, there is a practical lag. A state mandate that a city "shall adopt a land use regulation" does not rewrite the zoning map overnight. Cities have to draft, notice, and pass ordinance amendments. Some will move quickly; others will take months. Until your specific city updates its code, its permit counter may still be working off the old rules. The honest framing is: the right becomes enforceable October 1, 2026, but the local implementation arrives on each city's own schedule after that. Never treat this bill as "in effect now" or "legal statewide today" in mid-2026 — it is enacted, not yet operative.

Detached vs. Internal ADUs in Utah (HB 82 Background)

SB 284 did not come out of nowhere. It is the detached-unit companion to a law Utah passed five years earlier.

In 2021, Utah enacted H.B. 82 ("Single-family Housing Modifications"), which required municipalities to allow internal ADUs — units created within an existing single-family home — as a permitted use, subject to limits [4]. That law addressed the "basement apartment" and "in-home unit" case: converting existing interior space into a rentable dwelling. What HB 82 did not do was require cities to allow detached backyard units — standalone cottages, converted detached garages, and new accessory structures. That gap is exactly what SB 284 fills [1][4].

So Utah now has a two-part statewide framework:

Internal ADUs (inside the home): governed by the HB 82 (2021) framework. SB 284 did not change this statute; the internal-ADU provisions (renumbered in a late-2025 recodification of Utah's land-use code) remain as they were [4].
Detached ADUs (standalone structures): governed by the new § 10-21-304, operative October 1, 2026, on lots 11,000 sq ft or larger in specified municipalities [1].

One footnote to avoid a common mix-up: the content that became § 10-21-304 originated in a separate 2026 bill, H.B. 477 ("Land Use Regulation Revisions"), sponsored by Rep. Jill Koford. HB 477 did not pass as a standalone bill; its detached-ADU language was folded into S.B. 284, and Koford served as SB 284's House floor sponsor [1][5]. Separately, do not confuse SB 284 with H.B. 68 ("Housing and Community Development Amendments"), a different 2026 housing bill that is not an ADU statute [6]. If you are searching Utah's 2026 session for the detached-ADU rule, § 10-21-304 inside S.B. 284 is the one that counts.

What It Means for Homeowners vs. Investors

The honest read splits sharply depending on what you are trying to do.

If you own a single-family home on a lot 11,000 sq ft or larger in a covered city and want a backyard ADU for yourself or family, SB 284 is a clear win. Once the statute is operative and your city's ordinance is updated, you get a by-right path: no conditional-use hearing to lose, and parking capped at two spaces (one, if the unit is under 650 sq ft) [1]. Your project becomes a matter of meeting objective standards — size, setbacks, height, design, building code — rather than surviving a discretionary vote. That is a meaningful reduction in risk and timeline. The catch is timing: you cannot rely on it before October 1, 2026, and you should confirm your city has actually updated its code before you bank on the by-right treatment.

If you are an investor planning to rent out both units, slow down and read the local ordinance. SB 284 lets covered cities keep two provisions that can break an investor pro forma [1]:

Owner-occupancy. The city may require the owner to live in either the primary home or the ADU. If your model assumes both units leased to tenants, an owner-occupancy rule kills it.
90-day minimum rental. The city may prohibit rentals under 90 consecutive days, which shuts down short-term/nightly rental income. If your underwriting depends on Airbnb-style nightly rates, that assumption may not survive the local code.

Neither is guaranteed to apply — SB 284 only permits cities to impose them — but neither is prohibited either. So the investor's first move is not a spreadsheet; it is a call to the city to ask whether its post-SB 284 ordinance includes an owner-occupancy requirement and a 90-day rental floor. Get that answer before you make an offer on a lot.

How Utah Fits the Western ADU Trend

Utah's SB 284 lands in the middle of a broader Western pattern: state legislatures overriding local resistance to legalize accessory units, but doing it with very different mechanics from state to state.

Washington took a similar step in 2026 with HB 1345, another statewide detached-ADU authorization — but its structure is nearly the mirror image of Utah's. Washington's bill is permissive (counties "may" allow rural detached ADUs, subject to eleven conditions) rather than mandatory, and it targets rural parcels outside urban growth areas with a one-acre minimum. See our companion guide on Washington's HB 1345 rural ADU rules for how a permissive framework plays out differently than a mandate. Utah's SB 284, by contrast, is a mandate aimed at urban and suburban lots (11,000 sq ft, specified municipalities), which is a much more assertive posture toward local governments.

Oregon offers a third model. Its rural-ADU framework forces counties to allow units under specified conditions but caps size and imposes a two-acre minimum — see Oregon's rural ADU and septic rules. Across the three states, the common thread is state preemption of purely discretionary local denial; the differences are in whether the state requires or merely authorizes action, and whether the target is urban infill or rural land. Utah sits at the "urban, mandatory, but with generous local carve-outs" corner of that map.

What To Do Now

A practical sequence for a Utah homeowner or buyer eyeing a detached ADU under SB 284:

Confirm your city is a "specified municipality." Ask your city or county what class each is. If your city is not covered, SB 284's mandate does not apply and you are governed by local code alone [1].
Confirm your lot is 11,000 sq ft or larger and carries a permitted single-family dwelling. If it is smaller, check whether your city voluntarily allows detached ADUs on smaller lots — SB 284 permits but does not require this [1].
Check the calendar and the ordinance. The mandate is not operative until October 1, 2026, and your city then has to update its code. Ask the planning department whether its detached-ADU ordinance is adopted yet, and get the effective language in writing [1].
If you plan to rent, ask two specific questions: Does the city's ordinance require owner-occupancy? Does it impose a 90-day minimum-rental (short-term-rental ban)? Both are permitted by SB 284 and both can change your economics [1].
Explore the conversion path if you have an existing structure. If you own a legally built detached garage or outbuilding, ask about the mandatory conversion process — it may be a cheaper route than new construction [1].
Budget for what cities can still require: setbacks, height, lot coverage, design consistency with the main house, and a size cap that keeps the ADU no larger than the primary dwelling [1].

Frequently Asked Questions

Are detached ADUs legal statewide in Utah right now? Not yet, and not everywhere. SB 284 enacted the detached-ADU mandate (§ 10-21-304), but it is not operative until October 1, 2026, and it only binds "specified municipalities" — not every Utah city. After it becomes operative, covered cities must still update their ordinances. Do not treat detached ADUs as "already legal statewide" in mid-2026 [1][3].

What lot size do I need? The mandate applies to lots or parcels that are 11,000 square feet or larger and contain a permitted single-family dwelling. On smaller lots, SB 284 does not require anything — though your city is free to allow detached ADUs on smaller lots if it chooses [1].

Does my city have to allow a detached ADU? Only if it is a "specified municipality": a first-, second-, third-, or fourth-class city, or a fifth-class city of 5,000+ people located in a first-, second-, or third-class county [1]. If your city does not meet that definition, SB 284's mandate does not reach it, and local code controls.

Can my city still make me live on the property? Yes. SB 284 lets a covered city require owner-occupancy, satisfied by residing in either the primary dwelling or the ADU [1]. Whether your city imposes that is a question for your local ordinance.

Can I run the ADU as a short-term rental? Maybe not. SB 284 lets cities prohibit rentals shorter than 90 consecutive days, which effectively bans nightly/short-term rental where a city adopts that rule. Long-term rental is a different question and generally is not banned by the statute itself — but check your city's ordinance [1].

How does this differ from Utah's earlier ADU law? Utah's HB 82 (2021) required cities to allow internal ADUs inside existing homes. SB 284 is the detached counterpart, covering standalone backyard units and conversions of existing accessory structures. SB 284 did not change the internal-ADU law [1][4].

References

[1] Utah State Legislature, "S.B. 284 — Local Land and Water Modifications (Enrolled)." Enrolled bill text enacting Utah Code § 10-21-304 ("Detached accessory dwelling units"): the 11,000-square-foot permitted-use mandate, "specified municipality" definition, conditional-use and parking prohibitions (two spaces at 650+ sq ft, one below 650), the powers cities retain (size cap, setbacks, design consistency, front-yard ban, 90-day minimum rental, owner-occupancy, one-ADU limit, conversion path), and the special effective date (§ 10-21-304 effective 10/01/26; general effective date May 6, 2026). https://le.utah.gov/Session/2026/bills/enrolled/SB0284.pdf
[2] Utah State Legislature, "S.B. 284 — Local Land and Water Modifications (Bill Status)." Official status page for the bill, its sponsors, floor sponsor, and legislative history. https://le.utah.gov/~2026/bills/static/SB0284.html
[3] Utah State Legislature, "S.B. 284 Status Data Feed." Machine-readable status feed confirming the governor's action ("Governor Signed") and the March 18, 2026 signing date. https://le.utah.gov/data/2026GS/SB0284.json
[4] Utah State Legislature, "H.B. 82 (2021) — Single-family Housing Modifications." 2021 bill requiring municipalities to allow internal accessory dwelling units within existing single-family homes as a permitted use; the internal-ADU framework SB 284 did not change. https://le.utah.gov/~2021/bills/static/HB0082.html
[5] Utah State Legislature, "H.B. 477 (2026) — Land Use Regulation Revisions." Rep. Jill Koford's 2026 bill whose detached-ADU language did not pass standalone and was folded into S.B. 284. https://le.utah.gov/~2026/bills/static/HB0477.html
[6] Utah State Legislature, "H.B. 68 (2026) — Housing and Community Development Amendments." A separate 2026 housing bill that is not an accessory-dwelling-unit statute, noted here only to prevent confusion with SB 284. https://le.utah.gov/~2026/bills/static/HB0068.html