Detached ADU Cost in Utah (2026): What You'll Actually Pay
A detached ADU in Utah typically costs $200,000 to $400,000+ — roughly $250–$400 per square foot — because it's essentially a small new home with its own foundation, roof, and utility connections. Smaller standardized units on simple lots can start closer to $150,000. It's the right choice when privacy, family housing, or rental flexibility matter most, and not the cheapest path — a basement or garage conversion usually costs far less. Your real number depends on your lot, your city, what's in the way, and what's actually in your estimate.
Last verified: June 2026 · By the Utah ADU Builders editorial team
Who we are, plainly.
Utah ADU Builders is a Utah-focused ADU planning, feasibility, and builder-matching resource. We are not a city office, law firm, lender, licensed contractor, architect, engineer, or permit authority. We may earn compensation when homeowners request estimates or are connected with local professionals — but that does not change how we explain Utah's rules, costs, or risks. Cost figures here are planning estimates, not quotes, and local verification always governs.
An "ADU" (accessory dwelling unit) is a second, self-contained home on a single-family lot. An internal ADU is built inside the existing house (think basement apartment). A detached ADU — sometimes called a backyard cottage, casita, granny flat, or DADU — is a separate standalone structure. This page is about that detached type.
Detached ADU cost at a glance
| Detached ADU size | Typical all-in range (2026 estimate) | Notes |
|---|---|---|
| Small studio / 1-bed (≈400–600 sq ft) | $150,000–$220,000 | Highest cost per square foot; low end assumes a standardized unit on a simple site |
| Mid-size 1–2 bed (≈700–900 sq ft) | $200,000–$300,000 | Most common; usually the best value per sq ft |
| Larger 2-bed (≈1,000–1,200 sq ft) | $280,000–$400,000+ | Larger, custom, and higher-demand markets trend toward the top |
| Per square foot | ~$250–$400/sq ft | Higher than a larger home because fixed costs are spread over a small footprint |
What "all-in" should include: design and plans, permits, foundation, utility connections, sitework, construction, standard finishes, and inspections.
What it often does not include: financing costs, major utility or panel upgrades, unusual site or excavation work, landscaping repair, furniture, or rental licensing.
What we verified for this page (June 2026): Utah's S.B. 284 / Utah Code § 10-21-304 (read from the enrolled bill); the internal-ADU impact-fee exemption in § 11-36a-202; and detached-ADU rules from Salt Lake City, Salt Lake County, Draper, Provo, and Kaysville. Cost ranges are planning estimates triangulated from multiple Utah builder and vendor cost guides. Full sources are listed at the bottom.
A feasibility review narrows the planning range for your address.
No permit approval, financing, or builder availability is guaranteed.
See what kind of detached ADU your property may support →How much does a detached ADU cost in Utah?
A realistic planning range for a site-built detached ADU in Utah is $200,000 to $400,000+, with most mid-size projects (700–900 sq ft) landing around $200,000–$300,000. Smaller, standardized units on simple lots can start closer to $150,000, but that's a low-end scenario — not a safe default. The only number you can actually budget against is an all-in estimate for your lot, one that separates the structure from sitework, utilities, design, permits, and fees.
The honest version most cost pages skip: a detached ADU is not automatically a smart project just because Utah has made it easier to build one. S.B. 284 may make your lot newly eligible — but eligibility is not the same as affordability, and the right call depends on your lot, city, utilities, budget, and use case. The point of running feasibility first is to find out before you've spent money on design whether the numbers work for your situation.
Why detached ADUs cost more than a basement or garage conversion
Detached units cost more because you're building a small house from scratch, not finishing space you already own. A detached ADU needs its own foundation, framing, roof, siding, kitchen, bathroom, HVAC, electrical, plumbing, insulation, and utility connections — all the line items of a new home, just smaller.
The fixed-cost trap
A kitchen, a bathroom, a foundation, a roof, and utility hookups cost roughly the same whether the unit is 400 square feet or 900. Spread that fixed cost across a tiny footprint and your per-square-foot number spikes; spread it across a slightly larger unit and it drops. To illustrate the math (not as a quote): a 400 sq ft cottage might run around $170,000 while an 800 sq ft cottage runs around $250,000 — only about $80,000 more for twice the space. That's why moving from 400 to 800 sq ft often makes financial sense when your lot and city rules allow it.
What actually drives the price on your lot
The unit itself is fairly predictable. The surprises come from the ground. The biggest swing factor in Utah is getting water, sewer, and power from the street or main house to a backyard structure — and what's in the way.
| Cost driver | Typical range (estimate) | Why it varies |
|---|---|---|
| Utility trenching (water, sewer, electric to the backyard) | $5,000–$20,000+ | Distance, slope, rocky soil, and crossing existing driveways or landscaping |
| Sewer pump (if the lot lacks gravity-drainage grade) | +$3,000–$8,000 | Some lots can't drain to the ADU location by gravity and need a pump system |
| Design & engineering (construction drawings, often stamped) | $5,000–$15,000 | A new structure needs professional plans; complexity drives the fee |
| Permit fees | $1,000–$5,000 | Varies by city and project scope |
| Impact fees (see next section) | Varies widely by city | Charged for a new unit's impact on roads, parks, and utilities; confirm your city's schedule |
| Excavation / rocky soil | Highly variable | Common in parts of Draper, Cedar City, and foothill lots |
How we estimated these ranges: the figures above are planning buckets drawn from multiple Utah builder and vendor cost guides published in 2026 — not bids or official fee schedules. Permit and impact fees especially vary city to city, so confirm yours directly.
The single most expensive mistake: comparing the wrong numbers.
Before you trust any estimate, ask whether it includes: design/engineering, the foundation, utility trenching and connections, any panel or service upgrade, permit and plan-review fees, impact or connection fees, parking work, and concrete or landscaping repair. If those aren't in the number, the number isn't your budget.
Utility distance, drainage grade, and impact fees are parcel-specific.
A feasibility review narrows the planning range for your address.
Check your detached ADU feasibility and cost range →Permit fees, impact fees, and the internal-vs-detached difference
Permit fees for a Utah ADU typically run $1,000–$5,000. Impact fees — one-time charges a city levies for a new unit's demand on roads, parks, and utility systems — are where detached units differ sharply from internal ones, and it catches people off guard.
Internal ADUs
Under Utah Code § 11-36a-202, internal ADUs created inside an existing home are exempt from impact fees. This is a meaningful cost advantage over detached construction.
Detached ADUs
That exemption does not extend to detached new construction. Depending on how your city classifies the work, a detached ADU can be charged impact fees — Provo, for example, states on its official ADU page that detached units are subject to impact fees. Confirm your city's current schedule before you plan.
See our ADU permits guide and Utah ADU laws overview for the full permitting picture.
Is a detached ADU allowed on your lot? Utah's new S.B. 284 rules
For years, detached ADUs in Utah were left almost entirely to local zoning, and many cities banned them outright. That changed with S.B. 284, which created Utah Code § 10-21-304, effective October 1, 2026. We read the enrolled bill text directly, and here's what it actually does.
A "specified municipality" — defined in the statute as a city of the first, second, third, or fourth class, plus a fifth-class city of 5,000 or more residents located in a county of the first, second, or third class — must permit a detached ADU on any lot or parcel of 11,000 square feet or larger that already has a single-family home, where that home is a permitted use. Cities are free to allow detached ADUs on smaller lots too, but 11,000 square feet is the floor the state mandates.
That floor matters because it can override stricter local rules. Two limits to keep in mind: the section does not override restrictions on detached ADUs written into a development agreement a city signed on or before May 6, 2026, and it does not override other detached-ADU regulations a city is otherwise allowed to impose.
Cities may not (§ 10-21-304(3))
- ✕ Require a conditional-use permit for a detached ADU in a primarily residential zone
- ✕ Require more than two on-site parking spaces for a unit 650 sq ft or larger
- ✕ Require more than one parking space for a unit under 650 sq ft
Cities may still (§ 10-21-304(4))
- ✓ Regulate size, height, dimensions, and lot coverage
- ✓ Set setbacks from property lines and other buildings
- ✓ Require design consistency with the main home
- ✓ Require owner occupancy
- ✓ Require a 90-day minimum rental (effectively prohibiting nightly rentals)
- ✓ Require parking replacement when a garage is converted
- ✓ Limit one ADU per lot
- ✓ Deny if utilities can't support it (sewer, water, electrical, stormwater)
One more thing: check your HOA.
Utah law specifically bars homeowners associations from blocking internal ADUs, but that protection does not extend to detached units. If your neighborhood has CC&Rs (recorded covenants), they may still restrict or prohibit a detached cottage even where your city allows it — read your governing documents before you plan.
Eligibility under S.B. 284 is parcel-specific. Many cities are rewriting their codes through 2026.
A feasibility review confirms where your lot actually stands.
Start a Utah detached ADU feasibility review →Detached ADU rules by Utah city
Even where detached ADUs are allowed, each city sets its own lot minimums, setbacks, height caps, owner-occupancy, and metering rules — and those directly affect what you can build and what it costs. Here's a snapshot from official city and county sources. Treat it as a starting point, not a substitute for checking your specific parcel: these are the standards as currently adopted, and S.B. 284 is prompting cities to update them through 2026.
| Jurisdiction | Detached allowed? | Lot minimum | Key rules (from official sources) |
|---|---|---|---|
| Unincorporated Salt Lake County | Yes | 7,000 sq ft (6,000 in PC Zone) | At least 10 ft from the rear line and 6 ft from the main house; up to 20 ft tall or matching the home; one ADU per lot; can't be sold or subdivided; may be separately metered if the owner is billed for both; owner-occupancy affidavit and rental business license required; water/sewer availability confirmed before a permit issues |
| Salt Lake City | Yes | No minimum lot size | Detached ADUs capped at 1,000 sq ft gross floor area; max height 17 ft (up to 24 ft for a pitched roof or 20 ft for a flat roof with increased setbacks); 3 ft side and rear setbacks; one ADU per property; owner-occupancy required (limited exceptions); one parking stall (with transit/bike-lane exceptions); short-term rental of ADUs prohibited; a recorded restrictive covenant is required. Source: SLC Code 21A.40.200 |
| Draper | Yes | 12,000 sq ft | One ADU per lot; 30+ day rentals only; same setbacks as a house in the zone; primary dwelling must be owner-occupied; at least one extra non-tandem parking space; size capped at 50% of the primary dwelling; must match the home architecturally; height up to 35 ft; no separate utility meters. Note: Draper's 12,000 sq ft minimum is stricter than the new 11,000 sq ft state floor — expect this to be lowered; verify the current ordinance. |
| Provo | Expanding under S.B. 284 | Per S.B. 284 / local overlay | S.B. 284 expands detached eligibility beyond Provo's existing overlay; detached/external units are subject to impact fees, owner occupancy, separate utility meters, and long-term-rental rules |
| Kaysville | Not currently | — | Kaysville's current ADU page states that detached structures such as an apartment over a garage or a "granny flat" are not allowed as an ADU. As a specified municipality, Kaysville will likely need updated detached-ADU rules for qualifying parcels under S.B. 284 — verify the current code. |
Don't see your city, or your lot is an odd shape or size? Detached rules vary widely and many are mid-rewrite in 2026. A feasibility check confirms your specific parcel rather than a city-wide generality.
Detached ADU Cost Risk Scorecard
Before you spend a dollar on design, this is the fastest way to gauge whether a detached ADU is likely to be straightforward or expensive on your property. Count how many factors land in the right-hand column — the more there are, the more your project will trend toward the top of the cost range (or hit a feasibility wall).
| Factor | Lower-risk / lower-cost | Higher-risk / higher-cost |
|---|---|---|
| Lot size | 11,000+ sq ft, or a city that already allows smaller detached units | Under 11,000 sq ft in a city still updating its ordinance |
| Placement | Clear rear or side yard, no major easements | Front-yard or easement conflicts, awkward side-yard squeeze |
| Utilities | Short trench, known sewer/water/power access, good drainage grade | Long sewer run, panel upgrade, street connection, or a pump needed |
| Soil & access | Flat, stable, easy equipment access | Rocky soil, slope, or a narrow side yard |
| Parking | Existing parking preserved | A garage conversion that removes required parking |
| HOA | No HOA, or CC&Rs that allow detached ADUs | An HOA whose documents restrict detached units |
| Use & rental plan | Long-term family use or 90+ day rental | A short-term/nightly rental plan in a city that requires 90-day minimums |
| Budget expectation | $200k–$400k is realistic for your goals | Expecting a full legal detached unit at basement-conversion pricing |
The scorecard flags the risks; a feasibility review helps price them for your address.
How long does a detached ADU take to build in Utah?
Plan on roughly 8–12 months from signed contract to certificate of occupancy for a detached ADU, though smaller or simpler builds can land closer to 6–10 months. That includes a permit-review period that often runs several weeks to a couple of months before construction can start. Detached units take the longest of any ADU type because they're effectively new construction — a basement or garage conversion moves faster. Timelines depend on design, site conditions, utility work, permit review, and builder availability, so treat any single number as a planning estimate, not a promise.
A realistic detached ADU sequence:
Feasibility check → site and rule review → design and cost scope → permit application → plan review and corrections → utility/site prep → foundation, shell, and build → inspections → rental license and occupancy (if you're renting).
For a full breakdown by city and ADU type, see our Utah ADU timeline guide.
Is prefab or modular cheaper for a detached ADU in Utah?
Sometimes — but not as much as the sticker price suggests. Prefab or modular construction can make the structure portion of your budget more predictable and sometimes lower, and it can shorten the build. What it doesn't remove is most of what makes a detached ADU expensive in the first place: the foundation, utility trenching and connections, permit and plan review, your city's size/setback/height rules, delivery and crane/set, and site access. On a tight or sloped lot, those site costs can erase the factory savings.
If you're comparing a prefab quote to a site-built bid, ask the same all-in questions: does the price include the foundation, utility connections, design and engineering, permits, delivery and set, and meeting local code? A low building-only number on a hard site is not a low project number. This is also why the low end of the cost range (closer to $150,000) usually depends on a standardized unit and a simple, utility-friendly lot. For more on the prefab path, see our prefab ADU Utah guide.
Will rental income cover a detached ADU?
Rental income can help justify a detached ADU, but it should never be assumed. Whether the numbers work depends on your city's rental and owner-occupancy rules, short-term-rental restrictions, financing cost, vacancy, maintenance, insurance, taxes, and whether the unit is fully permitted. Rents vary widely by city, size, and finish — we won't quote a figure as a promise. A permitted ADU may also affect your property's assessed value and property taxes; confirm any impact with your county assessor or a tax professional, since it varies by property.
Use this simple worksheet to pressure-test your own assumptions before you commit:
| Input | Your number |
|---|---|
| Estimated all-in project cost | $______ |
| Realistic monthly rent for your area | $______ |
| Vacancy + maintenance reserve | $______ |
| Monthly financing payment | $______ |
| Added insurance / tax / utilities | $______ |
| Net monthly estimate | $______ |
| Break-even horizon | ______ years |
If the break-even horizon is long, or short-term rental was central to your plan in a city that requires 90-day minimums, that's a sign to slow down and confirm feasibility before designing anything. See our ADU rental income guide and ADU financing options for more.
Detached vs. basement vs. garage conversion — which path fits?
A detached ADU is usually the most private and flexible option, but it's also usually the most expensive. If a basement/internal ADU or a garage conversion fits your goals, those paths are typically far easier on the budget.
| ADU type | Cost direction | Best for | Not best for |
|---|---|---|---|
| Basement / internal ADU | Lowest | Existing space, lower budget, faster timeline | Privacy, no basement, HOA/rental limits |
| Garage conversion | Lower to mid | A solid existing garage with good utility access | Parking loss, weak structure, poor layout |
| Attached ADU | Mid to high | More privacy than a basement, shared infrastructure | Complex tie-in to the existing home |
| Detached ADU | Highest | Privacy, parents/adult kids, separate rental, long-term flexibility | Tight budgets, small lots, weak utilities |
For the full picture, see our Utah ADU cost guide, basement ADU cost guide, and garage conversion guide.
How we estimate detached ADU cost
Our practical view: a wide range gets you oriented, but only a property-specific review gets you a number worth budgeting against — because the biggest unknowns (utility distance, drainage grade, impact fees, and current city eligibility) are all tied to your exact parcel.
To be clear about what we are and aren't: we're a planning and builder-matching resource, not a contractor, architect, engineer, lender, or permit authority. Our estimate path starts with feasibility, not a fake instant quote — it considers your location, ADU type, property conditions, and intended use, then helps you compare practical next steps. The result is a planning estimate and a path forward, not a guaranteed bid, financing approval, or permit. Local verification is required before you design, finance, permit, rent, or build.
Frequently asked questions
What we verified for this page (June 2026)
- Utah state law: S.B. 284 / Utah Code § 10-21-304 (detached ADU requirements, effective Oct. 1, 2026), read from the enrolled bill; the "specified municipality" definition; and the internal-ADU impact-fee exemption in Utah Code § 11-36a-202.
- City and county rules: Salt Lake County's ADU ordinance; Salt Lake City's detached-ADU standards (size, height, setbacks, owner occupancy, short-term-rental prohibition); Draper's detached lot and design standards; Provo's ADU/impact-fee page; and Kaysville's current detached-ADU prohibition.
- Cost and timeline inputs: detached ADU price ranges, per-square-foot figures, utility/trenching costs, design fees, and build timelines, drawn from multiple Utah builder and vendor cost guides published in 2026 and labeled as estimates.
- Limitations: cost figures are planning estimates, not quotes; rental income, property-value increase, permit approval, financing, builder availability, and timelines are not guaranteed; and all city-specific rules require local verification, especially as ordinances update through 2026.
Sources we checked
- Utah Legislature — S.B. 284 (2026), enrolled (Utah Code § 10-21-304): le.utah.gov
- Utah Property Rights Ombudsman, ADU legal topics (incl. § 11-36a-202): propertyrights.utah.gov / commerce.utah.gov
- Salt Lake County, Accessory Dwelling Units: saltlakecounty.gov
- Salt Lake City ADU ordinance, 21A.40.200: codelibrary.amlegal.com
- City of Draper, Accessory Dwelling Units Permits: draperutah.gov
- Provo, Accessory Dwelling Units: provo.gov
- Kaysville, Internal Accessory Dwelling Units: kaysville.gov
- Utah ADU cost ranges: multiple Utah builder/vendor cost guides (used only for cost/timeline estimates, not legal claims)
City and state rules change — we re-verify this page periodically. For your property, current local rules and a professional review always govern.