How long does it take to get an ADU permit in Utah?

State law sets a 14-business-day benchmark for the initial building-plan review after a complete application reaches the right queue, and some cities publish similar targets. But that is first review, not final approval — corrections, a separate planning step, utility review, or rental licensing can extend it.

Does Utah's 14-business-day law mean my ADU is approved in two weeks?

No. The benchmark applies to the initial plan review after your application is accepted and complete. It doesn’t guarantee your plans are code-compliant, and it doesn’t cover the approvals some cities require before the building permit.

Which Utah city is fastest for ADUs?

There isn’t a reliable single answer, and we won’t name one without comparable citywide approval-cycle data. Cities with a permitted-use path and no separate pre-permit step — Salt Lake City is a good example — tend to move faster, but your ADU type and plan completeness usually matter more than the city’s name.

Which ADU type is fastest?

A straightforward internal or basement ADU is often the quickest path when the existing space is close to code. Detached ADUs generally take longest because they add site, foundation, utility, and separate-structure review.

Do detached ADUs get faster after Utah's 2026 law?

Sometimes. Where a city treats a detached ADU as a permitted use, the law bars requiring a conditional-use permit in a primarily residential zone, which can remove a public hearing and its scheduling delay. But not every city had that bottleneck to begin with — Salt Lake City, for example, already dropped conditional-use permits for ADUs — and building permits, utility work, and inspections still apply.

Can I start construction before my ADU permit is approved?

No. Starting work without an approved permit can lead to citations and doubled fees in Utah cities. Wait for the permit.

Does a prefab or tiny-home ADU get approved faster?

Sometimes the build is faster, but only if the city accepts the plans, the site works, and utilities are solved. Prefab can reduce design uncertainty; it does not bypass city review, permits, or inspections.

Does my HOA affect the timeline?

It can. A city may allow your ADU while an HOA covenant adds restrictions or a separate approval. Cities generally don’t enforce HOA rules, so budget it as its own step.

Utah ADU Timeline by City: Permits & Build Time (2026)

By Utah ADU Builders · Last verified: July 2026 · Sources: Utah Code §§ 10-21-303, 10-21-304, 10-20-909; city building and ADU pages

In Utah, your ADU timeline is mostly decided before construction starts — by the type of unit and your city’s approval steps, not by one universal number. Plan on roughly 3–6 months for an internal basement conversion and 9–18+ months for a detached backyard unit, from first call to move-in. State law puts a 14-business-day clock on the building-permit plan review, but that is not the same as final approval, and it is only one slice of the project.

Best for: homeowners weighing a specific ADU on a specific lot who need a realistic schedule to plan financing, a tenant, or a family move-in. Less useful if: you only want design inspiration — in that case the ranges below are all you need.

An “ADU” (accessory dwelling unit) is a second, self-contained home on the same lot as a single-family house — a basement apartment, a converted garage, an addition, or a standalone backyard cottage.

How this page works: Utah ADU Builders is a Utah-focused ADU planning, feasibility, and builder-matching resource. We are not a city, government office, law firm, lender, architect, engineer, licensed contractor, or permit authority. We may receive compensation when a homeowner requests a feasibility review or is connected with local professionals — but that never changes how we explain Utah’s ADU rules, timelines, or permitting risk. This is general information, not legal advice; rules change at both the state and city level, so verify specifics for your property before you rely on them.

✓ What we verified for this page

Utah’s building plan-review timeframe (state law) and how it applies to cities and counties
Utah’s internal-ADU law and its impact-fee exemption
Utah’s detached-ADU law taking effect October 1, 2026
Published permit-review targets and required pre-permit steps for the cities in our table, from each city’s own materials
City-specific friction that changes the timeline: predevelopment applications, separate land-use/ADU permits, site plan review, owner-occupancy rules, and rental licensing
Where a city does not publish an ADU-specific review target, we say so and rely on the statewide benchmark rather than invent a number. All cost and total-time figures are planning estimates.

In This Guide

Which ADU Path Moves Fastest?
Timeline by City
Start-to-Finish Phases
The “14 Business Days” Rule
Timeline by ADU Type
What Actually Slows ADUs Down
October 2026 Law Change
10-Point Feasibility Check
When a Timeline Is Too Optimistic
How We Estimated Timelines
FAQ
Sources

Quick answer: which ADU path tends to move fastest?

ADU path	Usually faster when…	Main timeline risk
Internal / basement ADU (built inside the existing home)	The space already exists and egress, ceiling height, and utilities are workable	Egress windows, fire separation, panel capacity, correction cycles
Garage conversion	The garage is structurally sound and parking can be replaced	Replacement parking, foundation/slab, fire separation, utilities
Attached ADU (an addition sharing a wall)	A simple addition with clean setbacks and nearby utilities	Structural tie-in, design, engineering, inspections
Detached ADU (a standalone structure)	Lot size, access, setbacks, and utilities are favorable	Site plan review, utility runs, separate structure, impact fees
Prefab / modular ADU	The design is set and the site is ready	City review and site/utility work still control the schedule

Utah ADU timeline by city

The fastest city is not always the one with the shortest published review target. A complete internal-ADU application in a city with a clean process can beat a detached ADU in the same city once site plan review, utilities, and setbacks come into play. This table separates what each city actually requires — because the presence or absence of a separate approval step before the building permit is the single biggest reason timelines differ.

A note that applies to every Utah city: state law sets a 14-business-day benchmark for a city to complete the initial plan review of a one- or two-family dwelling or townhome (21 business days for multifamily), and counties operate under a parallel benchmark (Utah Code § 10-20-909 for municipalities; § 17-79-810 for counties). That clock covers the building-permit review only — not the pre-permit approvals before it, not the correction cycles after it, and not construction.

City / area	Separate approval before building permit?	Detached ADU status	Key timeline factors
Salt Lake City	No separate step No separate conditional-use approval for standard ADUs (the city eliminated ADU conditional-use permits), but the building-permit review still involves zoning, planning, and other departments, and even a pre-approved standard plan requires a site review before a permit issues.	Allowed; capped at 1,000 sq ft, up to 24 ft with an added setback. Owner-occupancy required (limited exceptions).	Pre-approved standard ADU plans are available; the city publishes a 14-business-day first-review target and reviews departments at the same time; expedited review is offered for a higher fee.
South Salt Lake	Yes — extra step Yes — an ADU Predevelopment Application ($50) must be reviewed and approved by Planning before a building permit can be processed.	Allowed under the city's ADU code.	The 15-business-day target is the general building-permit review target, separate from (and after) the predevelopment approval. Owner or immediate-family occupancy; annual rental license; one additional parking site.
Salt Lake County (unincorporated)	Confirm current rules Written confirmation from your water provider is required before a permit is issued; a pre-application check is recommended.	Allowed (internal lots ≥ 6,000 sq ft; detached ≥ 7,000 sq ft, except in the PC Zone where 6,000 sq ft may qualify).	A recorded owner-occupancy affidavit and a rental business license are required; a separate address marker is required.
Provo	No separate step A building permit is required for any construction or remodeling, and a Rental Dwelling License is required to rent the unit.	Allowed with standards (its own address; a detached unit needs a separate meter); detached units can be charged impact fees. The home must be an owner-occupied single-family dwelling.	The ADU must clear permitting and rental licensing before it is a legal rental.
Ogden	Yes — extra step Yes — a separate accessory-dwelling (land-use) permit is required in addition to building permits; the Planning Division issues it after Building and Fire review, and the certificate is recorded with the county recorder.	Allowed; detached units are 300–800 sq ft and can't cover more than 25% of the rear yard.	Owner-occupancy required; the ADU permit is voided when the property sells, so a new owner must reapply.
Lehi	Confirm current rules Development-code standards and a site plan apply.	Historically required a 14,520 sq ft minimum lot; under the new state law the city must allow detached ADUs on lots ≥ 11,000 sq ft and may require two off-street stalls for units over 650 sq ft.	Rules are in transition in 2026 as the city updates its code to the state standard.
Millcreek	Yes — extra step Yes — a detached ADU requires a Planning & Zoning site plan review, and an ADU application must be completed with Planning & Zoning before a building permit can be applied for.	Allowed; detached units need a lot of at least 8,000 sq ft (internal/attached have no lot-size minimum, though internal is barred below 6,000 sq ft).	The owner must live on the property to rent; a business license is required to rent; short-term rentals are prohibited in detached ADUs.
Draper	Yes — extra step Yes — every ADU (rented or not) requires an ADU permit to verify compliance; a building permit is separate for any construction.	Allowed; Draper has required a larger minimum lot for detached units (reported at 12,000 sq ft), which the new 11,000 sq ft state floor affects — confirm the current standard. An eligibility map governs internal ADUs.	Owner-occupancy required (either unit); one added parking space (no tandem); a separate ADU address is assigned.
Orem	Confirm current rules Owner-occupancy required; the city's public ADU guidance centers on accessory apartments within the main home.	Detached-ADU rules are in transition and should be confirmed with the city after the October 2026 state changes.	Confirm the current accessory-apartment/ADU application steps before budgeting your timeline.
Layton	No separate step A permit is required.	Allowed — ADUs are permitted in all single-family residential zones.	Short-term rental of the ADU is not permitted; HOA rules can be more restrictive than city code and are enforced by the HOA, not the city.
Sandy	Yes — extra step Yes — an accessory apartment requires both a Special Use Permit and a business license.	The city's public materials center on accessory apartments; confirm detached-ADU standards with the city.	Owner-occupancy required (notarized affidavit); only owners holding at least 50% of the property may apply; the business license renews annually.
St. George	Confirm current rules A site plan is submitted to Community Development for a compliance check before a building permit is issued (for a guesthouse/casita).	Allowed only on a parcel that has a single-family dwelling; one ADU or guesthouse per lot (two within the Downtown Boundary).	Owner-occupancy required; short-term rental of an ADU is not permitted; one added off-street parking space (no tandem).

Cities update ADU rules often — especially through the October 2026 detached-ADU transition — and many more Utah cities (Kaysville, Bountiful, Herriman, West Jordan, South Jordan, Murray, Taylorsville, Cottonwood Heights, and others) have their own ordinances. Some add a separate planning or site-plan step for detached units. If your city isn’t listed, the one question that most affects your timeline is simple: does my city require a separate ADU or land-use approval before I can pull a building permit?

Sources for the table above (each city’s own materials; last checked July 2026): Salt Lake City Building Services and SLC Code 21A.40.200 · South Salt Lake ADU and Building Permits pages · Salt Lake County Office of Regional Development ADU guide · Provo City ADU page and Provo City Code 14.30.030 · Ogden City ADU application and Code 15-13-39 · Lehi City Detached ADU Development Code Amendment · Millcreek ADU page and Code 18.71/19.89 · Draper City ADU Permits page · Orem City accessory-apartment page · Layton City FAQ · Sandy City accessory-apartment standards · St. George City Code 10-17A-3 and 10-17A-7.

Not sure how your city stacks up?

See what kind of ADU your property may support and get a sense of your approval path before you spend on plans.

How long does an ADU take in Utah, start to finish?

The honest total is months to over a year, because an ADU is a sequence of phases — and the phase that trips up most homeowners isn’t construction, it’s the city approval that can come before you’re even allowed to pull a building permit. Design, that approval layer, plan review, construction, and final inspection each add time, and the mix depends on your city and your ADU type.

Phase	What happens	Who controls it	Typical range (estimate)	Does it vary by city?
1. Feasibility & design	Confirm the lot qualifies; produce site plan, floor plans, and engineering	You + your designer	2 weeks – 4 months	A little
2. Pre-permit city approval	Some cities require a separate ADU/land-use permit, a predevelopment application, or a site plan review before the building permit	Your city	0 – 8+ weeks	A lot — this is the big variable
3. Building-permit plan review	The city reviews your plans for building-code compliance	Your city (state-law clock)	~2 weeks for a first pass, plus correction cycles	Less than people think
4. Construction	Site work, foundation, framing, trades, finishes	Your builder	6 weeks – 8+ months	No — driven by ADU type
5. Final inspection, occupancy & rental license	Certificate of occupancy; rental/business license if you'll rent	Your city	1 – 4+ weeks	Somewhat

Two takeaways most guides skip. First, Phase 2 is where one city pulls ahead of another — not the plan-review clock in Phase 3. Second, homeowners routinely under-budget Phases 2 and 5, then blame the city for being “slow” when the real issue was sequence.

Why “14 business days” doesn’t mean your permit is approved in two weeks

Utah’s 14-business-day plan-review benchmark is real, but it is not a promise that your ADU is approved in two weeks. It refers to the initial building-plan review after your application is accepted, complete, and in the correct queue (Utah Code § 10-20-909 for municipalities; § 17-79-810 for counties). It does not cover the approvals some cities require before the building permit, and it does not cover what happens after a first review.

Three things regularly turn “two weeks” into two months or more:

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First review is not final approval. A first review usually produces either an approval-to-issue or a list of corrections. Corrections and resubmittals can pause or extend the timeline, and each re-review adds time.
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The application has to be complete first. Missing site plans, elevations, utility details, or an owner affidavit can keep the clock from ever meaningfully starting. In cities with a predevelopment or separate ADU permit step, that approval happens before the building-permit clock begins at all.
▼
Approval and legal rental can be separate. Passing a building inspection does not automatically make every rental use legal. Several cities require a separate rental or business license — Provo's ADU Rental Dwelling License and Sandy's accessory-apartment business license are two examples — so your legal rental timeline can run past your construction timeline.

Our practical view: you can’t speed up the state review clock, but you win time by clearing the approval layer early and submitting complete, code-ready plans.

Get a property-specific timeline before you spend on design

Check ADU feasibility for your lot and city — before you commit to a builder's schedule.

Timeline by ADU type: internal, garage, attached, detached, prefab

Your ADU type usually matters as much as your city. An internal or basement conversion can move quickly when the existing space is close to code; a detached ADU behaves more like a small new home — foundation, utilities, site plan, separate structure — so it takes longer. These are planning estimates, not guarantees; site conditions, plan completeness, financing, and contractor scheduling all move them.

ADU type	Realistic planning estimate	What speeds it up	What slows it down
Internal / basement	~3–6+ months	Existing space; workable egress, ceiling height, parking, utilities	Structural changes, egress windows, panel upgrades, rental licensing
Garage conversion	~4–7+ months	A garage that's genuinely convertible	Replacing lost parking, fire separation, insulation, slab/foundation
Attached (addition)	~5–9+ months	Simple addition, clean setbacks, utilities nearby	Engineering, foundation, design, exterior match, inspections
Detached (site-built)	~9–18+ months	Favorable lot and utility path; a pre-approved plan on a simple lot can land near the low end	Site plan review, sewer/water/electric runs, engineering, impact fees, custom design
Prefab / modular	~5–10+ months	A set design and a ready site	City review and utility hookups still control the calendar

A word on prefab, because it’s often oversold on speed. A modular unit can be built in a factory while site work happens in parallel, which can compress the construction window — but it does not skip permits, plan review, or inspections, and your city’s approval steps are unchanged. We partner with Nest Tiny Homes, a modular ADU provider; a feasibility review can tell you whether a modular or a site-built path is the better fit for your lot, budget, and city. We don’t call any single provider “best,” and modular is not automatically faster once permitting is counted. For more detail, see our prefab ADU Utah guide.

What actually slows an ADU down in Utah

Most ADU delays come from a mismatch between the project a homeowner pictures and the review path their city actually requires. The big ones are predictable, which means most are avoidable.

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Incomplete plans. Missing details trigger extra correction cycles, and each cycle costs weeks.
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A separate planning step you didn't budget for. Predevelopment applications (South Salt Lake), separate land-use/ADU permits (Ogden, Draper), and site plan review for detached units (Millcreek, St. George) must clear before — or alongside — the building permit.
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Owner-occupancy and rental rules. Most Utah cities require the owner to live on the property and require a rental or business license to rent the unit.
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Parking and driveways. Losing a garage to a conversion can require replacement parking and a redesign.
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Utilities and impact fees. Detached units raise more utility questions. Utah law exempts building an internal ADU — one created within your existing home — from impact fees (a one-time charge cities levy on new development for roads, parks, and utilities). That exemption is specific: it doesn’t waive every fee, and a detached ADU can be charged impact fees. For more, see our guide to Utah ADU permit fees by city.
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HOA or private covenants. Your city may allow an ADU while your HOA's CC&Rs add restrictions or a separate approval. Cities generally don't enforce private HOA rules, so treat that as its own step.
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Winter. Concrete pours and framing can stall in a Wasatch Front winter, which quietly adds weeks to detached builds.

What changes on October 1, 2026: Utah’s detached-ADU law

Effective October 1, 2026, Utah’s detached-ADU law (SB 284, codified at Utah Code § 10-21-304) requires qualifying municipalities to allow detached ADUs as a permitted use on lots of at least 11,000 square feet — reducing a city’s ability to block them outright on larger lots. It does not make every detached ADU fast or automatic, and cities keep meaningful control.

What the law does for timelines

Where a detached ADU becomes a permitted use, the law bars a city from requiring a conditional-use permit in a primarily residential zone — a discretionary approval that can require a public hearing and add weeks of scheduling and uncertainty. Removing that step is a real timeline win on qualifying lots.

What cities can still regulate

Height, setbacks, design compatibility, parking, owner-occupancy, one-ADU-per-lot limits, utility capacity, and rental-duration rules. A city may also prohibit a detached ADU from being larger than the single-family dwelling on the same lot. Building permits, plan review, and inspections all still apply.

Why timelines may feel less predictable for a while

Cities are actively rewriting code and checklists to match the new floor. Lehi, for example, is lowering its detached-ADU minimum from 14,520 sq ft to the state's 11,000 sq ft and adjusting parking and size rules. During this transition, confirm your city's current detached-ADU standards rather than assuming last year's rules.

Before you pay for plans: a 10-point feasibility check

Before you spend on full drawings or take a builder’s timeline at face value, work through this. The fastest project is the one that matches your city’s cleanest path — not the one that looks cheapest on a napkin sketch.

1
Confirm which city or county actually has jurisdiction over your address.
2
Pick the ADU type: internal, garage, attached, detached, or prefab/modular.
3
Check the owner-occupancy rule for your city.
4
Define your goal: family/in-law use, long-term rental, extra space, or resale.
5
Check lot size and setbacks (a setback is the minimum distance a structure must sit from a property line).
6
Check parking and driveway impacts, especially for a garage conversion.
7
Map the utility route: sewer, water, electric, gas, and stormwater.
8
Find out whether your city requires a predevelopment application, site plan review, or a separate ADU permit before the building permit.
9
Identify who will produce permit-ready plans and any required engineering.
10
Understand the final steps: inspections, certificate of occupancy, and any rental or business license.

If several of these are unknowns, the smartest next move is a feasibility check — not a rushed quote.

Get a property-specific read before you commit to plans

Compare practical build options for your lot and city before requesting builder estimates.

When an ADU timeline is probably too optimistic

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 use case — and when several timeline risks stack up, feasibility beats optimism. These are the red flags that a “few months” plan is really a year-plus plan:

⚠You're assuming 'allowed' means 'approved.'
⚠You want a detached ADU but haven't checked lot size, setbacks, easements, utilities, or access.
⚠You're converting a garage and haven't solved replacement parking.
⚠You're counting on short-term rental income, but your city restricts or bans ADU short-term rentals (a short-term rental is typically a stay under 30 days; many Utah cities allow ADUs only as long-term rentals).
⚠You have an HOA and haven't checked its covenants.
⚠You don't yet know whether a rental license, business license, or occupancy step applies.
⚠You have no plan for sewer, water, electric, stormwater, or fire access.
⚠You're treating concept renderings as permit-ready plans.

None of this means don’t build. It means find out what’s real before you pay for drawings — which is exactly what a feasibility review is for.

How we estimated these timelines

We separate official facts from planning estimates so you can see where the certainty ends. Here’s the method behind the numbers on this page:

We reviewed Utah’s state ADU and plan-review law, including the internal-ADU rules (§ 10-21-303), the detached-ADU law effective October 1, 2026 (§ 10-21-304), and the municipal and county plan-review benchmarks.
We checked each listed city’s official building and ADU pages for published review targets or required pre-permit steps.
We separated three different things people call “the timeline”: first review, permit approval, and total build time.
We built the total-time-by-type ranges from the real stages every project passes through — feasibility, design, city approval, corrections, permit issuance, construction, inspections, and occupancy or rental licensing.
Where a city publishes no ADU-specific review target, we lean on the statewide benchmark and say so, rather than inventing a city-specific number.
These ranges are planning estimates to help you budget time, not measured averages. We date-stamp our sources and re-check them, especially through the October 2026 detached-ADU transition.

Utah ADU timeline FAQs

Every project is different, and the only timeline that matters is the one for your lot, your city, and your ADU type. A feasibility review turns the ranges above into a property-specific plan — and a realistic cost path — before you request builder estimates.

Request a Utah ADU Feasibility Review

Get a property-specific timeline and fee path before you request builder estimates — not a generic range.

Utah ADU Builders may receive compensation when homeowners request estimates or are connected with local professionals. We are not a city permitting office and cannot guarantee approval, timelines, fees, financing, rental income, or builder availability.

Sources

Utah state law and official state guidance:

Utah Code § 10-21-303 (internal ADUs; municipalities) and § 17-80-303 (counties)
Utah Code § 10-21-304 (detached ADUs; effective October 1, 2026), enacted by SB 284 (2026 General Session) — le.utah.gov
Utah Code § 11-36a-202 (internal ADU impact-fee exemption)
Utah Code § 10-20-909 (municipal plan-review timeframe) and § 17-79-810 (county plan-review timeframe)
Utah Department of Commerce, Office of the Property Rights Ombudsman — ADU legal topic (propertyrights.utah.gov)

City and county sources:

Salt Lake City Building Services — permitting process and ADU standard plans (slc.gov); Salt Lake City Code 21A.40.200
South Salt Lake — ADUs page and Building Permits page (sslc.gov)
Salt Lake County (unincorporated) — Accessory Dwelling Units guide (saltlakecounty.gov)
Provo City — ADU page (provo.gov) and Provo City Code 14.30.030
Ogden City — ADU application (ogdencity.gov) and Ogden City Code 15-13-39
Lehi City — Detached ADU Development Code Amendment, State Requirements (engagelehi.org)
Millcreek — Accessory Dwelling Units page (millcreekut.gov) and Millcreek Code 18.71
Draper City — Accessory Dwelling Units Permits page (draperutah.gov)
Orem City — Accessory Apartments page (orem.gov)
Layton City — FAQ (laytoncityutah.gov)
Sandy City — Accessory Apartments standards (sandy.utah.gov)
St. George City Code 10-17A-3 and 10-17A-7 (stgeorge.municipal.codes)

Official first-review targets are not total project timelines. They typically begin after an application is accepted, complete, or in the correct review queue. Corrections, planning review, utility issues, inspections, and construction scheduling extend the overall timeline.

Related guides: