Last verified: July 2026 · By the Utah ADU Builders Editorial Team
Utah ADU Laws: Internal, Detached, City, and HOA Rules in 2026
Utah law gives many homeowners a real path to build an accessory dwelling unit (ADU) — a second, self-contained home on a single-family lot — but it is not a blank check. Internal ADUs (a unit inside your existing home, like a basement apartment) are already protected statewide. Detached ADUs (backyard cottages and garage apartments) get a much stronger path in most larger cities starting October 1, 2026. This page is for Utah homeowners deciding whether an ADU is feasible, not a permit approval or legal advice.
Utah ADU laws at a glance
| Question | Bottom line |
|---|---|
| Are ADUs legal in Utah? | Often yes — but it depends on the ADU type and your city. |
| Internal ADU (basement or in-home unit) | A permitted use in residential zones statewide since 2021, if it meets the state definition: inside an owner-occupied single-family home, within the existing footprint, rented 30+ days. |
| Detached ADU (backyard cottage, garage apartment) | Starting October 1, 2026, larger Utah cities — those the law calls "specified municipalities," not every town or unincorporated county area — must allow one on a lot of 11,000 sq ft or larger that has a single-family home, where single-family homes are already allowed. Cities may allow smaller lots too. |
| Attached ADU (addition with its own entrance) | Mostly governed by your city's ordinance — no blanket statewide guarantee. |
| Can my city add rules? | Yes — parking (within limits), setbacks, height, size, design, owner-occupancy, and licensing, within what state law allows. |
| Can my HOA block it? | It generally cannot block a compliant internal ADU, but it may still restrict or prohibit a detached ADU. |
| Can I short-term rent it? | Don't assume so. Internal ADUs are for 30+ day rentals; for detached ADUs, cities may bar rentals under 90 days. |
| Do I need a permit? | Almost always. Construction or remodeling needs a building permit, and renting may require an ADU permit or rental license — don't build or rent without the required local approvals. |
Want your city's rules first? Jump to the Utah city ADU rule snapshot below.
What we verified
We checked this page against primary and official sources, current as of July 2026, and note the source under each major section:
- Utah state statute — the internal ADU law (Utah Code § 10-21-303), the new detached ADU law (Utah Code § 10-21-304, effective October 1, 2026), definitions (§ 10-21-101), and the impact-fee exemption (§ 11-36a-202).
- S.B. 284 (2026 General Session) — the enrolled bill that added the detached ADU requirement.
- Utah Office of the Property Rights Ombudsman and Utah Department of Commerce guidance.
- Official city ADU pages for the cities in our snapshot table (linked in the table, checked July 2026).
We did not use builder marketing claims, and we do not state any figure for guaranteed rental income, property value, financing approval, permit approval, or construction timeline — Utah ADU law guarantees none of those.
Are ADUs legal in Utah right now?
Yes — but "legal in Utah" depends entirely on your ADU type and where you live. State law protects internal ADUs almost everywhere, gives detached ADUs a much stronger path in most larger cities beginning October 1, 2026, and leaves attached additions and many details up to your city. Every ADU still needs the right approvals.
The mistake that gets homeowners in trouble is reading a headline — "Utah legalized ADUs" — and assuming their city must approve their exact basement apartment, garage conversion, or backyard cottage without conditions. That is not how it works. Utah sets a baseline; your city fills in the specifics that usually decide whether a project is practical.
Which Utah ADU law applies to your project?
| Your project | Likely category | Main rule source | Practical warning |
|---|---|---|---|
| Basement apartment inside your owner-occupied single-family home | Internal ADU | State law (§ 10-21-303) | Still needs code compliance, a local permit/license, and parking/owner-occupancy/rental checks. |
| Mother-in-law suite inside the home, rented long-term | Internal ADU (if it meets the definition) | State law | Family use vs. rental use can change how a city treats it. |
| Attached addition built beyond the home's existing footprint | Usually attached ADU | Local ordinance + building code | Don't assume the statewide internal-ADU protection applies. |
| Backyard cottage (separate structure) | Detached ADU | State law from Oct. 1, 2026 (§ 10-21-304) in most larger cities, plus local rules | The 11,000 sq ft threshold and city design rules still apply. |
| Detached garage converted to a living unit | Detached ADU | Detached ADU law + local rules | Setbacks, fire/building code, parking replacement, and utilities can decide feasibility. |
| Tiny home or prefab unit | Depends on foundation, classification, and use | Local ordinance + building code | A tiny home on wheels is not automatically an ADU. |
What Utah's internal ADU law actually allows
An internal ADU is the strongest statewide protection a Utah homeowner has — but it is narrow. Under Utah Code § 10-21-303, an internal ADU is a permitted use in areas zoned primarily for residential use, meaning your city generally can't force a discretionary hearing to approve one that meets the standards.
To qualify as an internal ADU under state law, the unit must be:
- created within your primary dwelling and within its existing footprint at the time it's created,
- in a detached single-family home occupied as the owner's primary residence, and
- used for a long-term rental of 30 consecutive days or longer.
A basement apartment is the classic example. And one meaningful cost advantage: construction of an internal ADU is not subject to impact fees (Utah Code § 11-36a-202) — a break that does not automatically extend to detached units.
What your city can still require or restrict for an internal ADU
State law lets cities attach specific conditions. Yours may:
- require one additional on-site parking space (and replacement of garage/carport parking if you convert the garage),
- require an ADU permit or rental license,
- prohibit a separate utility meter,
- require egress and other life-safety code items (such as a bedroom egress window) and a single-family exterior appearance,
- prohibit internal ADUs on lots of 6,000 sq ft or smaller,
- prohibit short-term rentals (under 30 days),
- require owner occupancy, and
- exclude internal ADUs from a limited slice of the city — a district covering up to 25% of the area zoned primarily residential (up to 67% in a city with a university of 10,000+ students).
For unincorporated county areas, the parallel internal-ADU statute is Utah Code § 17-80-303.
One more protection worth knowing: where an internal ADU otherwise complies with local land use, building, health, and fire codes, an HOA generally cannot ban it by CC&R or rule. (Detached ADUs are different — more on that below.)
Sources: Utah Code § 10-21-303 (municipalities) and § 17-80-303 (counties); § 11-36a-202 (impact fees); Utah Office of the Property Rights Ombudsman.
What changes for detached ADUs on October 1, 2026?
This is the biggest recent change in Utah ADU law, and it's the one most homeowners haven't caught up on. For years, whether you could build a backyard cottage was entirely up to your city. Under S.B. 284 (2026), that changes: beginning October 1, 2026, Utah Code § 10-21-304 requires most larger cities to allow a detached ADU — a separate structure not attached to the main home — as a permitted use on qualifying lots.
Where the requirement applies
A "specified municipality" must adopt a rule permitting a detached ADU on any lot or parcel that is 11,000 sq ft or larger and contains a single-family dwelling, if single-family homes are a permitted use there. A "specified municipality" is defined in law as a city of the first through fourth class (generally cities of roughly 10,000 or more residents), plus a fifth-class city of 5,000 or more located in a first-, second-, or third-class county. In practice, that covers most of Utah's city-dwellers but not every small town or unincorporated county area.
Cities may also choose to allow detached ADUs on lots smaller than 11,000 sq ft — many already do. So a lot under the state floor isn't automatically a "no"; it just isn't guaranteed by the state.
What your city cannot do (for a qualifying detached ADU)
Under § 10-21-304, a city's detached-ADU rule may not:
- require a conditional use permit if the detached ADU is in a primarily residential zone,
- require more than two on-site parking spaces for a detached ADU that is 650 sq ft or larger,
- require more than one on-site parking space for a detached ADU smaller than 650 sq ft, or
- impose design standards that conflict with the state's building-design-element limits.
The law also requires cities to include a process for converting a legally built accessory structure (like an existing detached garage) into a detached ADU, subject to setback and building/health/fire codes.
What your city can still control
The state sets a floor, not a free-for-all. A city may still:
- apply rules on size, height, lot coverage, and setbacks (including proximity to property lines, easements, and window orientation),
- require the ADU to be designed consistently with the main house,
- prohibit a detached ADU that is larger than the main house, sits in a utility easement, or sits in the front yard,
- require owner occupancy (owner living in either the main home or the ADU),
- prohibit rentals of fewer than 90 consecutive days,
- require replacing garage parking when a detached garage is converted,
- limit the lot to one ADU, and
- deny a detached ADU if the utilities (sewer, water, power, storm water) can't adequately serve or don't have capacity for it.
One important exception
The detached-ADU requirement does not override a prohibition or restriction on detached ADUs contained in a development agreement a city signed on or before May 6, 2026, or other lawful land-use or administrative actions not prohibited by law. If your property sits inside an older master-planned community or an entitlement-controlled development, that agreement may still limit or bar a detached ADU even after October 1, 2026 — worth checking before you plan.
Detached vs. internal: two more practical differences
- Impact fees. The impact-fee exemption above applies to internal ADUs. A detached ADU may be subject to impact fees and utility hookup costs, which can be significant.
- Short-term rentals. Internal ADUs are tied to 30+ day rentals; for detached ADUs a city may prohibit rentals under 90 consecutive days.
Detached ADU law, in one table
| Issue | Detached ADU rule (Utah Code § 10-21-304, effective Oct. 1, 2026) |
|---|---|
| Covered cities | "Specified municipalities" (most cities of ~10,000+, plus 5,000+ cities in larger counties) |
| Baseline lot size | 11,000 sq ft or larger |
| Existing home required | Yes — the lot must have a single-family home, where single-family use is allowed |
| Smaller lots | Cities may choose to allow them |
| Conditional use permit | Not allowed for a detached ADU in a primarily residential zone |
| Parking cap | No more than 2 spaces (unit ≥ 650 sq ft); no more than 1 space (unit < 650 sq ft) |
| Short-term rental | City may prohibit rentals under 90 consecutive days |
| Still up to your city | Size, height, setbacks, lot coverage, design, owner occupancy, one-ADU limit, utility capacity |
| Doesn't override | Detached-ADU limits in a development agreement signed on or before May 6, 2026 |
Because this takes effect October 1, 2026, cities are updating their ordinances now — some, like Provo, are already expanding detached-ADU eligibility, while others are still drafting. If your city's older code bans detached ADUs or requires a very large lot, that restriction may no longer hold on an 11,000+ sq ft lot once the city conforms to state law.
Source: Utah Code § 10-21-304 (effective October 1, 2026), enacted by S.B. 284, 2026 General Session, Utah State Legislature.
Do you have to live on the property? (owner occupancy)
Often, yes — and it depends on your city. State law lets cities require owner occupancy for both internal and detached ADUs, and many Utah cities do. If you're an investor hoping to rent both the main home and the ADU, this is the single rule most likely to change your plan, so confirm it for your specific city before you design anything.
For an internal ADU, the statewide definition itself is tied to a home occupied as the owner's primary residence. For a detached ADU, the city may require the owner to live in either the main home or the ADU.
Can you Airbnb a Utah ADU or use it as a short-term rental?
Do not assume you can. Internal ADUs under state law are defined around long-term rental use — 30 consecutive days or longer — and cities routinely prohibit short-term (nightly) rentals in them. For detached ADUs, § 10-21-304 lets a city prohibit rentals of fewer than 90 consecutive days. A project that works beautifully for family housing or a long-term tenant may not be legal as a short-term rental, so treat any Airbnb-style plan as needing city-specific verification.
Can an HOA stop a Utah ADU?
For an internal ADU, generally no. For a detached ADU, possibly yes. State law protects a compliant internal ADU from an HOA blanket ban. It does not give detached ADUs the same protection — so your HOA's governing documents (CC&Rs) may still restrict or prohibit a detached backyard unit even if state law and your city otherwise allow one.
If you live in an HOA community and you're considering a detached ADU, read your CC&Rs early. It's one of the most common late-stage surprises, and it's easy to check before you spend on plans.
Sources: Utah Office of the Property Rights Ombudsman; Utah Department of Commerce (HOA guidance).
Utah ADU rules by city (2026 snapshot)
Because your city controls the details, the same ADU can be straightforward in one city and difficult in the next. The snapshot below shows how several Utah cities handle ADUs as of July 2026, with a link to each city's official page.
| City | Owner occupancy? | Detached ADU | Short-term rental in ADU? | Official source |
|---|---|---|---|---|
| Salt Lake City | Yes — owner must remain on the property (limited exceptions) | Allowed; conditional-use hurdles removed in 2023 | Sub-30-day use generally not permitted in residential ADU zones | SLC Planning |
| Provo | Yes (limited temporary-absence exceptions) | In transition — expanding under state law (11,000+ sq ft is the state floor); city notes SB 284 details may still change | Long-term; rental dwelling license required | Provo ADU page |
| Draper | Yes | Allowed; historically required ~12,000 sq ft — the 11,000 sq ft state floor applies once the city conforms (Oct. 1, 2026) | 30+ day rentals only | Draper ADU permits |
| Millcreek | Yes (year-round) | Allowed; detached generally needs ~8,000 sq ft, up to ~1,000 sq ft, in the rear yard | Prohibited in detached; allowed for internal/attached with a license | Millcreek ADU page |
| Kaysville | Yes | Current city code does not allow detached units (e.g., garage apartments, granny flats); in transition due to the Oct. 1, 2026 state law | No | Kaysville IADU page |
| Cottonwood Heights | Yes (affidavit) | Currently requires conditional-use approval and extra parking; those may be limited for qualifying detached units once the city conforms (Oct. 1, 2026) | No | Cottonwood Heights ADU page |
| South Salt Lake | Yes | Allowed in R1/RM zones; 6,000 sq ft minimum; ADU predevelopment approval required before a building permit | No | South Salt Lake ADUs |
| Logan | Yes | Allowed (all ADU types, following 2024 code updates); external units are height-limited | Regulated separately (the ADU-specific short-term-rental ban was removed in 2024) | Logan ADU page |
Cities like Ogden, Lehi, and Sandy are also updating their detached-ADU codes to meet the new state requirement. If your city isn't listed, the safest path is to confirm your own lot's situation rather than assume a neighbor's rules apply.
For a full city-by-city breakdown, see our Utah ADU rules by city guide. County-level guides: Salt Lake County · Davis County · Weber County.
Do Utah ADUs need permits before you build or rent?
Don't build or rent without the required local approvals. "Permitted use" means you don't need a special zoning hearing — it does not mean you can skip permits. Construction or remodeling typically requires a building permit, and every ADU must meet building, health, and fire codes (egress, fire separation, ceiling heights, and utilities among them). Depending on your city, renting may also require an ADU permit, a rental dwelling license, a business license, an inspection, or a predevelopment approval — and some cities keep those steps separate from the building permit. Contractor licensing and owner-builder eligibility can also depend on your project's scope and local rules, so verify before assuming you can pull the permit yourself.
A note on a common worry: many homeowners have a finished basement or a "mother-in-law apartment" a previous owner or agent called "legal." That history doesn't guarantee it complies with current code or was ever permitted. Renting or selling an unpermitted unit can create real problems — enforcement, safety issues, and complications at resale. If you're in this situation, a feasibility check is a low-risk way to understand where you actually stand before you rent it out or list the home.
Sources: Utah Code § 10-21-303 and § 10-21-304 (building, health, and fire code compliance); individual city permit and licensing pages.
For city-specific permit steps and what to expect, see our Utah ADU permit process guide.
Utah ADU feasibility checklist: what to verify before you spend on plans
The right first step isn't a builder quote — it's feasibility. A Utah ADU can be blocked or reshaped by any one of the factors below. Walk through this list before you fall in love with a floor plan.
- Jurisdiction — city or unincorporated county
- Your existing home — detached single-family, townhouse, duplex, or other
- ADU type — internal, basement, garage conversion, attached addition, detached cottage, or prefab
- Lot size — the 6,000 sq ft internal-ADU floor a city may impose, and the 11,000 sq ft detached-ADU threshold
- Zoning district and any overlays
- Owner-occupancy plan — will you live on-site?
- Rental plan — long-term, family use, or short-term (which is often restricted)
- HOA / CC&Rs — especially for a detached unit, and any development agreement on the property
- Parking — extra spaces required, and any garage conversion that removes existing parking
- Utilities — water, sewer, power, storm water capacity, and hookup costs
- Septic or sewer status
- Easements and front-yard placement
- Building-code items — egress, fire separation, ceiling heights, exits
- Budget and financing path
- Whether an existing detached structure was legally built
Feasibility scorecard
| Factor | Lower-friction sign | Higher-risk sign |
|---|---|---|
| ADU type | Internal basement in an owner-occupied home | Detached unit in an HOA or on a small lot |
| Rental plan | Long-term or family use | Short-term / nightly rental plan |
| Lot | Large, clear lot | Small lot, tight setbacks, easements |
| Parking | Existing off-street space | Garage conversion removes required parking |
| Utilities | Sewer/water/power capacity available | Septic, limited service, or upgrades needed |
| Local rules | City has a clear ADU process | City rules in transition or unclear |
| HOA | No ADU restriction / internal ADU | Detached ADU limited by CC&Rs or a development agreement |
What Utah ADU law does not guarantee
An ADU isn't automatically a smart project just because Utah has become more ADU-friendly. The right project depends on your lot, city, utilities, budget, and use case. Being honest about that up front saves people real money.
Specifically, Utah ADU law does not guarantee:
- Permit or HOA approval. Your project still has to meet local rules and code.
- Rental income or short-term-rental use. Rental terms are restricted, and market and tenant outcomes vary.
- A property value increase. Value effects are specific to your property and market — be wary of anyone promising a fixed percentage.
- Low cost or a fast timeline. Utility upgrades, hookup fees, impact fees (on detached units), site conditions, and city permitting all move the numbers.
If a detached ADU is the goal but your lot is small, your HOA restricts it, or utilities would need major upgrades, the smartest move may be to pause, price the constraints, or consider an internal ADU instead. A feasibility review is the safer next step than committing to plans.
How much does a Utah ADU cost, and how long does it take?
It varies widely by type and site — enough that a single number would mislead more than help. A basement or garage conversion that reuses an existing footprint is generally the least expensive path; a new detached structure is generally the most. The biggest cost drivers are site prep, utility capacity and hookup costs, impact fees (which can apply to detached units), size, and finishes — and timelines depend heavily on your city's permitting queue.
For current cost ranges and what changes them, see our Utah ADU cost guide, and for how long projects take, our Utah ADU timeline guide. Then confirm your own numbers with a feasibility review.
What to do next if you're not sure which Utah ADU law applies
The safest next step is a property-specific feasibility check that identifies your likely ADU type, your city and HOA friction, parking and utility issues, rental limits, and a rough cost path — before plans, bids, financing assumptions, or contractor deposits.
A good feasibility process asks for your address or city, the ADU type you're considering, your lot size, your existing home type, your HOA status, your owner-occupancy and rental plans, and your budget. In return, you should get a clear read on the likely ADU category, the rule-friction flags on your property, a cost-path range, and an honest answer to the only question that matters at this stage: does it make sense to get builder estimates yet?
Related ADU resources
Utah ADU laws FAQ
Primary sources we checked (July 2026)
- Utah Code § 10-21-101 (definitions), § 10-21-303 (internal ADUs), § 10-21-304 (detached ADUs, effective October 1, 2026), and § 17-80-303 (counties) — Utah State Legislature
- Utah Code § 11-36a-202 (internal ADU impact-fee exemption)
- S.B. 284, 2026 General Session — Utah State Legislature
- Utah Office of the Property Rights Ombudsman — Accessory Dwelling Units
- Utah Department of Commerce — HOA and ADU guidance
- City ordinance and planning pages (linked in the snapshot table): Salt Lake City, Provo, Draper, Millcreek, Kaysville, Cottonwood Heights, South Salt Lake, and Logan
This page is general information for Utah homeowners, not legal advice. ADU rules change, and cities are still adopting new ordinances, so confirm the current statute and your city's ordinance before you rely on them.