Utah ADU Laws Changelog: What Changed, What's Current, and What Still Depends on Your City
Utah's ADU rules have changed in two ways that actually affect your project. Since 2021, internal ADUs — a second unit inside your home, like a basement apartment — have been a permitted use in most residential zones statewide. Since October 1, 2026, a new law has required specified municipalities to allow detached ADUs — a separate backyard unit — on qualifying lots of 11,000 square feet or larger.
This page is for Utah homeowners deciding whether to build. It is not legal advice, and your city, lot size, and utilities still decide what's actually possible.
Check your ADU feasibilityOn this page
- Utah ADU law at a glance
- The Utah ADU law changelog
- Internal vs. detached ADUs
- What changed for 2026?
- What HB 82 changed for internal ADUs
- Does Utah allow detached ADUs statewide?
- What did not change
- Which law applies to my project?
- How cities are rolling out the rules
- Cost estimates
- What to verify before spending money
- FAQs
- Sources
State law checked: October 3, 2026. City examples: July 2026 unless stated otherwise; Lehi’s published code was rechecked October 3. The detached-ADU requirement is now in effect. Review the relevant sources again after a statute or local ordinance changes.
A quick note on who we are: Utah ADU Builders is a Utah-focused ADU planning, feasibility, and builder-matching resource. We may receive compensation when homeowners request a feasibility review or are connected with local professionals. That compensation does not change how we report Utah ADU law, dates, citations, or the risks below. We are not a city, government office, law firm, lender, licensed contractor, architect, engineer, or permit authority.
What we verified for this page:
- Utah state law: HB 82 (2021), SB 284 (2026), and the current Utah Code sections for internal and detached ADUs (§10-21-303, §10-21-304, §17-80-303) and impact fees (§11-36a-202).
- Plain-language state guidance: the Utah Office of the Property Rights Ombudsman's ADU explainer.
- Official city and county sources: Provo, Lehi, and Salt Lake County ADU pages, used as real examples of how cities are implementing the state rules.
- Cost figures: treated as current third-party estimates, not quotes — see the cost note below for what changes them.
Full source links are listed at the bottom of this page.
Utah ADU law at a glance
Here is the current picture in one place. Details vary by city — this is the statewide floor, not the whole rulebook.
| Question | Current answer |
|---|---|
| Are internal (basement) ADUs legal statewide? | Yes — a qualifying internal ADU is a permitted use in most residential zones (since October 1, 2021). |
| Are detached (backyard) ADUs legal statewide? | The requirement is now in effect in specified municipalities: first-, second-, third-, or fourth-class cities, plus fifth-class cities of at least 5,000 residents located in first-, second-, or third-class counties. It applies to qualifying lots of 11,000 sq ft or larger that contain a single-family dwelling, where that dwelling is a permitted use. It does not cover every town or unincorporated county area. |
| What law controls internal ADUs? | Utah Code §10-21-303 (cities) and §17-80-303 (counties). |
| What law controls the new detached-ADU rule? | Utah Code §10-21-304, effective October 1, 2026. See city-by-city lot size requirements. |
| Do I still need a permit? | Yes — assume local approval is required. Construction or conversion needs a building permit; renting typically needs a local license. |
| Can my city still add rules? | Yes — setbacks, size, design, parking, owner-occupancy, and utility limits are still largely local. |
"Permitted use" means allowed by right — a qualifying unit can't be forced through a discretionary public hearing. "Conditional use" is the slower, case-by-case approval that permitted-use status removes.
Timeline of Utah ADU law changes from HB 82 (2021) to SB 284 (2026)
HB 82 took effect
Internal ADUs became a permitted use in most residential zones statewide.
§10-21-303Code renumbered
Utah recodifies its land-use code. Internal ADU rules move from §10-9a-530 to §10-21-303.
§10-9a-530 → §10-21-303SB 284 took effect
Detached ADUs became a required permitted use on qualifying lots (11,000 sq ft+) in covered cities.
§10-21-304Concept timeline only. Verify final details with your city before purchasing plans or applying for permits.
The Utah ADU law changelog
Three state-level changes matter to homeowners. Two changed what you can build; one changed the statute numbers (which is why so many other websites now cite the wrong law).
| When | What changed | ADU type | Current citation | What it means for you |
|---|---|---|---|---|
| 2021 effective Oct 1, 2021 | HB 82 made internal ADUs a permitted use in most residential zones statewide, and limited HOA/CC&R rules from prohibiting a qualifying internal ADU rental. | Internal ADUs | §10-21-303cities; §17-80-303 counties | A basement or in-home unit is allowed by right in covered zones — but the home must be owner-occupied, and cities can still require permits, parking, and more. |
| Late 2025 effective Nov 6, 2025 | Utah renumbered and amended its land-use code (a recodification). The internal-ADU rules carried over; the section numbers changed. | Citation change | §10-9a-530→ §10-21-303 | If a page still cites §10-9a-530, it predates this update. The current internal-ADU sections are §10-21-303 and §17-80-303. |
| 2026 effective Oct 1, 2026 | SB 284 requires specified municipalities (first-, second-, third-, or fourth-class cities, plus fifth-class cities of at least 5,000 residents located in first-, second-, or third-class counties) to allow detached ADUs as a permitted use on qualifying lots of 11,000 sq ft or larger with a single-family home. | Detached ADUs | §10-21-304 | A backyard cottage may now be possible where your city previously said no — but the city still controls setbacks, size, parking, and utilities. |
Cities also update their own ordinances on their own schedules. For example, Salt Lake County adopted ADU ordinance changes on June 4, 2024. The detached-ADU state requirement took effect October 1, 2026; older city pages may not show current implementation. The state law sets a floor, while each city's current ordinance and permit process provide property-specific details.
Quick citation check
If you're comparing sources, this is the fastest way to spot an outdated one:
⚠ Outdated
Cites §10-9a-530 for internal ADUs, or says detached ADUs "always require conditional-use approval."
✓ Current
Cites §10-21-303 / §17-80-303 for internal ADUs, and reflects the §10-21-304 detached-ADU rule that took effect October 1, 2026.
Internal vs. detached ADUs in Utah
These are two different legal categories with two different rules. Most confusion comes from treating them as one.
| Internal ADU (inside the home) | Detached ADU (separate structure) | |
|---|---|---|
| What it is | A unit within your existing home's footprint, such as a basement apartment | A standalone unit in the yard, such as a backyard cottage or a unit over a detached garage |
| Statewide status | Permitted use since Oct 1, 2021 | Required under §10-21-304 in specified municipalities since Oct 1, 2026 |
| Statute | §10-21-303 (cities) / §17-80-303 (counties) | §10-21-304 |
| State lot-size floor | Cities may exclude lots 6,000 sq ft or smaller | Covered cities must allow on lots 11,000 sq ft or larger (they may allow smaller) |
| Owner-occupancy | Built into the definition — the primary home must be a detached single-family home occupied as the owner's primary residence; cities may also bar renting an internal ADU if the owner doesn't live there | Cities may require the owner to live in the main home or the ADU |
| Parking | Cities may require one extra off-street space (and replacement parking if a garage is converted) | Covered regulations may require no more than two on-site spaces assigned to a detached ADU of 650 sq ft or larger, and no more than one for a unit under 650 sq ft; garage conversion can require replacement parking for the main home |
| Short-term rental (nightly) | Defined around long-term rentals of 30+ days; cities may prohibit short-term rental | Cities may prohibit renting a detached ADU for fewer than 90 consecutive days — don't assume nightly rental is allowed; verify your city |
| Impact fees | Construction of an internal ADU within an existing primary dwelling is exempt from impact fees (§11-36a-202(2)(a)(vi)) | The internal-ADU impact-fee exemption does not automatically apply — local fees may apply; verify |
A setback is the required distance between a structure and your property line. An impact fee is a one-time charge some cities levy to fund infrastructure like roads, water, or sewer.
What changed in Utah ADU law for 2026?
The 2026 change is about detached ADUs. Under Utah Code §10-21-304, effective October 1, 2026, "specified municipalities" must allow a detached ADU on a lot of 11,000 square feet or larger that contains a single-family home, in zones where single-family homes are already permitted. It's the biggest shift since 2021 — but it's a floor, not a guarantee for every property.
Who and what the rule covers
The statute uses “specified municipality.” Utah Code §10-21-101(25) defines it as first-, second-, third-, or fourth-class cities, plus fifth-class cities of at least 5,000 residents located in first-, second-, or third-class counties. A single population cutoff is not enough to determine coverage. The rule applies when all of these are true:
- The city meets the specified-municipality definition in §10-21-101(25)
- The lot is 11,000 square feet or larger
- The lot already has a single-family home on it
- The lot is in a zone where a single-family home is a permitted use
Cities are free to be more generous — several already allow detached ADUs on smaller lots.
What covered cities cannot do
- ✕Treat a qualifying detached ADU as a slow, discretionary conditional use in a covered residential zone
- ✕Require more than two on-site parking spaces assigned to a detached ADU of 650 sq ft or larger, or more than one for a detached ADU under 650 sq ft
- ✕Impose design standards that conflict with the state's limits on building-design elements
What cities can still control
- →Size, height, and lot coverage
- →Setbacks and placement
- →Design compatibility with the primary dwelling
- →Owner-occupancy requirements
- →Short-term rental limits (fewer than 90 consecutive days)
- →Utility access and capacity
- →One-ADU-per-lot limits
Why "detached ADUs are legal now" is too simple
The law creates a statewide floor for covered cities and qualifying lots. It does not eliminate permits, building and safety codes, setbacks, utility requirements, or local design rules — and it does not apply equally to every town, every lot, or every rental plan. State law controls where it preempts local rules; your local ordinance and permit standards control the property-specific details that state law leaves to the city or county.
What did HB 82 change for internal ADUs?
HB 82, passed in 2021, is the earlier change that created Utah's statewide internal-ADU framework. It required cities to treat qualifying internal ADUs as a permitted use in residential zones — meaning no conditional-use hearing for a unit that meets the standards — and its ADU provisions took effect October 1, 2021. The current statute now appears at §10-21-303 after the 2025 renumbering.
An internal ADU means inside an owner-occupied home
This is the category most people mean by "basement apartment" or "converting part of the house." Under Utah law, an internal ADU is created within the footprint of a detached single-family home that the owner occupies as their primary residence, for a long-term rental of 30 consecutive days or longer. In other words, owner-occupancy isn't an optional city add-on for internal ADUs — it's part of what qualifies the unit in the first place.
HB 82 did not remove all local rules
| Common assumption | Accurate version |
|---|---|
| "HB 82 made every ADU legal everywhere." | No — it addressed internal ADUs and still let cities impose several allowed restrictions. |
| "My city can't require anything." | No — cities can still require code compliance, a permit or rental license, parking, and appearance standards, among others. |
| "I can Airbnb my internal ADU." | Don't assume so — internal ADUs are tied to 30+ day rentals, and cities may prohibit shorter rentals. |
| "Owner-occupancy doesn't matter anymore." | It still does. The internal-ADU protection applies to an owner-occupied home, and cities may bar renting an internal ADU if the owner doesn't live on-site. |
| "A garage conversion is automatically easy." | Cities can require replacement parking when a garage or carport becomes living space. |
Internal ADUs and impact fees
According to the Utah Office of the Property Rights Ombudsman, construction of an internal ADU within an existing primary dwelling is exempt from impact fees (§11-36a-202(2)(a)(vi)). Be careful not to stretch that into "ADUs have no fees." This exemption does not automatically cover detached ADUs, utility-connection charges, permit fees, or local review costs.
Does Utah now allow detached ADUs statewide?
The 2026 law is powerful, but it is not a blanket approval. Since October 1, 2026, a covered city must adopt a regulation permitting a detached ADU on a qualifying lot of 11,000 square feet or larger — but the city can still regulate setbacks, size, height, coverage, design, owner-occupancy, parking, utilities, and more. Lot size is one factor, not the whole answer.
The 11,000 sq ft rule is a floor, not a ceiling
Cities may allow detached ADUs on smaller lots, and some already do. For example, Salt Lake County's guidance lists a 7,000 sq ft minimum for detached ADUs (and 6,000 sq ft in one specific zone) — more permissive than the statewide floor. So "my lot is under 11,000 sq ft" does not automatically mean "no."
Detached ADU feasibility signals to check before you buy plans
| Signal | Why it matters |
|---|---|
| Your city / jurisdiction | The state sets a floor; local implementation controls the details. |
| Lot size | 11,000 sq ft triggers the state rule, but some cities allow smaller lots. |
| Existing single-family home | The 2026 rule depends on a lot that already has one. |
| Zoning | The path is tied to zones where single-family homes are permitted. |
| Setbacks and easements | A large lot can still have a small usable build area. |
| Utilities | Sewer, water, electrical, and stormwater capacity can block or complicate a build. |
| Parking | Cities can still require limited on-site parking. |
| Owner-occupancy | Cities can still require it for detached ADUs. |
| HOA / private covenants | A separate, document-specific question — don't assume state law resolves it. |
What did not change after Utah's ADU updates?
Utah made some projects easier, but it did not remove local review. ADUs can still be delayed, redesigned, or made more expensive by permits, building code, utilities, parking, setbacks, HOA rules, owner-occupancy, rental limits, and site conditions. The updates opened doors — they did not remove the doorway.
| Misunderstanding | Accurate version |
|---|---|
| "Utah legalized all ADUs everywhere." | Utah created statewide rules for internal ADUs and a 2026 detached-ADU floor for covered cities — but local rules and property-specific feasibility still decide. |
| "No permits needed." | A building permit is required for construction or conversion; renting typically also needs a local license. |
| "I can list it on Airbnb." | Internal ADUs are tied to 30+ day rentals; for detached ADUs, cities may prohibit rentals shorter than 90 consecutive days. Verify before assuming. |
| "Impact fees are gone for all ADUs." | The verified exemption covers internal-ADU construction within an existing primary dwelling (§11-36a-202(2)(a)(vi)); other permits, licenses and utility fees may still apply. |
| "The city can't require owner-occupancy." | For internal ADUs, owner-occupancy is built into the definition; for detached ADUs, cities may require it. |
| "A big lot means I can build." | Setbacks, easements, utilities, parking, and city rules can still stop or shrink a project. |
An ADU is not automatically a smart project just because Utah has become more ADU-friendly. The right project depends on your lot, city, utilities, budget, and how you plan to use it. The lowest-risk move is to confirm feasibility before you spend money on plans, prefab deposits, or builder quotes.
Which Utah ADU law applies to my project?
The law that matters depends on the type of ADU. A basement unit, a backyard cottage, and a garage conversion can each follow a different path.
| Your project | Main legal path | What to verify next |
|---|---|---|
| Basement / internal ADU (inside the home) | §10-21-303 internal-ADU framework | Owner-occupancy, city eligibility, permit/license, parking, code compliance |
| Internal garage conversion connected to the home | | Replacement parking, egress, fire/health/building code |
| Detached backyard cottage | §10-21-304 (from Oct 1, 2026) + city rules | Lot size, whether your city is covered, zoning, setbacks, utilities, parking |
| Detached garage conversion | | Legal construction status, setbacks, code upgrades, utility access |
| Attached addition | | City classification, building permit, setbacks, utilities |
| Tiny home / prefab / modular unit | | Whether it qualifies as an ADU, foundation, utility connection, local review |
| Short-term rental plan | | Don't assume nightly rental is allowed |
How Utah cities are rolling out the new rules
City implementation is where a statewide law becomes an address-specific answer. Three examples show why the same state law lands differently in different places.
Provo's official guidance notes that SB 284 calls for cities of 5,000 or more to allow detached ADUs on qualifying lots of at least 11,000 square feet, and that SB 284 covers detached/external ADUs only — not internal or basement ADUs.
Provo also states that a lot must have a single-family home to be eligible, and that ADUs still go through the city's permitting and rental-licensing process before becoming a legal residence.
Lehi’s current published Development Code §26.040 lists a minimum 11,000 sq ft lot, and its amendment history includes July 14, 2026. The unit’s finished living area must be smaller than the primary home, and only one ADU is allowed per lot. The current PDF parking text says two stalls above 650 sq ft and one below 650 sq ft but does not expressly resolve exactly 650; state law caps the requirement at two for a unit of 650 sq ft or larger. Confirm the city’s application of its code at that boundary. Lehi Development Code Chapter 26, checked October 3, 2026.
The county adopted ADU ordinance changes on June 4, 2024, and its guide lists local eligibility — including internal ADUs on lots of at least 6,000 sq ft and detached ADUs on lots of at least 7,000 sq ft (6,000 sq ft in one specific zone).
Note that this is the county's own guidance for the areas it governs (unincorporated Salt Lake County); incorporated cities within the county have their own ADU ordinances, so check the city your property is in.
The takeaway: some places are more permissive than the state floor, and all of them keep meaningful local control. Always confirm your own city or county. See our Utah County ADU guide and Davis County ADU guide for more city-by-city breakdowns.
What will it cost? (estimates, not quotes)
Costs depend heavily on ADU type and site conditions, so treat these as rough planning ranges from third-party sources, not a bid. A commonly cited 2026 range for Utah ADU projects is roughly: design $5,000–$15,000, permit fees $1,000–$5,000, and construction $80,000–$250,000+. Basement and garage conversions tend to sit at the low end; new detached structures at the high end.
What pushes costs up
- ↑Separate utility connections
- ↑Difficult site conditions (grade, rock, access)
- ↑Custom design
- ↑High-end finishes
What keeps costs down
- ↓Reusing an existing footprint (basement or garage)
- ↓Staying within your lot's utility capacity
- ↓Simpler designs
Your actual number depends on your property — a feasibility review is how you turn a range into a real figure. For a fuller breakdown, see our Utah ADU cost guide.
What to verify before you spend money on ADU plans or estimates
The smartest next step after reading about the law is not to call a builder — it's to confirm the change actually helps your property, ADU type, city, lot, and use case.
| Verify this | Why it matters |
|---|---|
| Your city / jurisdiction | Neighboring cities apply the state rules differently, and not every city is covered by the detached-ADU rule. |
| ADU type | Internal, detached, garage conversion, and prefab each follow different paths. |
| Lot size | Drives both internal-ADU limits and detached-ADU eligibility. |
| Zoning | The state rules depend on the local zoning context. |
| Existing single-family home | Required for most ADU pathways. |
| Setbacks and easements | A lot can be legally large but hard to build on. |
| Utilities | Sewer, water, electrical, and stormwater capacity can change feasibility. |
| Owner-occupancy | Built into the internal-ADU definition; a possible requirement for detached ADUs. |
| Rental plans | Long-term vs. short-term rules differ by ADU type and city. |
| Existing unpermitted work | Basement or garage conversions may need correction first. |
| HOA / covenants | A legal, document-specific question worth checking early. |
| Budget and financing | A project can be legal but still not the right financial move. |
How Utah ADU Builders verifies what's on this page
Our practical view is that ADU advice is only useful if it's current, so we check law claims against official sources before turning them into guidance. Our source order is: (1) the current Utah Code, (2) Utah Legislature bills and history, (3) the Utah Office of the Property Rights Ombudsman for plain-English interpretation, and (4) official city and county pages for local implementation. We use homeowner forums and reviews only to understand common questions — never as proof of law.
What this page is not: it is not legal advice, not a permit approval, and not a guarantee that your city, HOA, utility provider, or lender will approve a project. It does not promise a construction timeline, rental income, or an increase in property value. For decisions specific to your property, confirm your city's ordinance and consider professional advice.
See our full editorial standards and advertising disclosure for more on how we operate.
Utah ADU laws: frequently asked questions
Related guides
Utah ADU Laws — Current Rules
The evergreen current-rules companion to this changelog.
Can I Build an ADU in Utah?
City-by-city feasibility breakdown.
Detached ADU Builders Utah
Backyard cottage and separate-structure options.
Utah ADU Permit Guide
Permit steps, timelines, and what to expect.
Utah ADU Cost Guide
Cost ranges by type, city, and project scope.
ADU Financing Utah
HELOC, loans, and programs to pay for your ADU.
Utah ADU Statistics 2026
What the verified data shows — and what it doesn't.
Sources
- Utah Legislature — HB 82 (2021), Single-family Housing Modifications
- Utah Legislature — SB 284 (2026), Local Land and Water Modifications (enrolled)
- Utah Legislature — recodification tables (2025 land-use renumbering)
- Utah Code — Title 10, Chapter 21 (§10-21-303; §10-21-304)
- Utah Office of the Property Rights Ombudsman — Accessory Dwelling Units
- City of Provo — Accessory Dwelling Units
- City of Provo — SB 284 eligibility notice
- City of Lehi (Engage Lehi) — Detached ADU Development Code Amendment (State Requirements)
- Salt Lake County — Accessory Dwelling Units (Office of Regional Development)
- Cost figures are current third-party planning estimates and vary by project and site.
Start a Utah ADU feasibility review
The law is only half the story. Your city, lot size, utilities, zoning, and budget decide what's actually buildable on your property. Check your feasibility before requesting quotes or purchasing plans.
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