ADU Cost Utah: 2026 Prices by Type, City & the Hidden Costs Most Quotes Miss

ADU cost by type: which one fits your property?

The type you build is the largest cost lever you control. Conversions reuse an existing shell and tend to cost less; new construction adds a foundation, utilities, and a full building envelope and tends to cost more. Here's how each plays out in Utah.

Basement or internal ADU — usually the cheapest path

Plan on roughly $60,000–$150,000. An internal ADU (a unit created inside your home's existing footprint, like a basement apartment) is often the lowest-cost option because the structure, roof, and foundation already exist. It also carries a real legal edge: under Utah law, building an internal ADU inside your existing home is not subject to impact fees — the one-time charges cities levy on new development for things like parks, roads, and utilities (Utah Code §11-36a-202). That exemption applies specifically to internal ADUs inside an existing single-family home, not to detached or attached additions.

It stops being cheap when the basement lacks legal ceiling height, safe egress (a code-compliant way out in an emergency), a separate entrance, good sewer slope, or fire separation between units. Older homes may also need an electrical panel upgrade.

Garage conversion — affordable, but rarely as simple as it looks

Plan on roughly $60,000–$175,000. Walls and a roof already exist, which helps — but garages aren't built like living space. Common surprises: an uninsulated or sloped slab, no plumbing nearby, a new HVAC system, an exterior that has to be reworked, and parking replacement. Several Utah cities require you to replace the off-street parking you lose when you convert a garage, which can erase part of the savings.

Attached addition — more separation without a separate building

Plan on roughly $150,000–$275,000. An attached ADU is new square footage built onto your home with its own entrance. It's a middle path: more privacy than a basement, less than a standalone cottage. Cost drivers are foundation work, tying a new roofline into the existing house, structural engineering, and extending utilities.

Detached backyard ADU or casita — the most expensive, and the most flexible

Plan on roughly $200,000–$400,000+. A detached ADU is a separate structure in your yard — essentially a small new house, which is why it tops the range. You're paying for a new foundation, a full envelope, separate heating and cooling, and trenching to run sewer, water, and electrical out to the unit. Those utility connections, the trenching, and the available capacity can add materially to the bill. In return you get the most privacy and a fully separate, self-contained unit.

Detached ADUs are also where Utah's 2026 law changes the picture — more on that below.

Concept image; actual design, cost, and approval depend on site and local rules.

Prefab or modular ADU — faster, but the sticker isn't the total

Plan on roughly $150,000–$300,000+ installed. Factory-built units can simplify design and shorten the build. The trap is comparing a factory package price to a fully installed, permitted, utility-connected total. Site prep, foundation, crane and access, utility connections, permits, and local compliance still apply — and on a tight or sloped lot they add up fast.

What a property-specific estimate actually weighs

A useful Utah ADU estimate isn't just a cost-per-square-foot figure times your size. To get close to a real range, it has to account for:

• Your city or county — rules, fees, and the 2026 detached-ADU rollout all vary by jurisdiction
• ADU type and your target size
• Whether you have an existing shell (basement, garage) or are building new
• Utility distance and capacity — how far sewer, water, and electrical are, and whether there's room on the system
• Slope and site access
• Parking you may need to add or replace
• Any HOA or recorded restrictions on the property
• Finish level and your intended use (family housing, long-term rental)

That's what our instant estimate asks about — and it's why two homes on the same street can land at very different numbers.

How ADU cost changes by Utah city

Two identical ADUs can cost very different amounts in two Utah cities, because labor, infill access, utility rules, impact fees, parking, owner-occupancy requirements, and detached-ADU eligibility all vary — and the 2026 detached-ADU law is rolling out city by city. The table below is a planning framework, not a list of official city prices.

Want a deeper look at city-by-city rules, permit fees, and lot requirements? See our dedicated guide: Utah ADU Cost by City (2026).

The specific rules noted below are examples from the named jurisdictions. Where nearby cities are grouped in one row, treat the specific rule as the named city's and verify your own city separately. Ranges are planning estimates, not bids or official city pricing. Curious how we build these ranges? Read our cost methodology.

Here's a concrete example of why "what does an ADU cost in Utah?" has no single answer: Provo requires a detached ADU to have its own separate utility meter, South Jordan prohibits separate meters entirely, and unincorporated Salt Lake County takes a different approach still. City rules genuinely change the budget — treat your specific city's adopted ordinance as the thing you build against, not the state average.

The hidden costs that change your final price

The "hidden" costs usually aren't extras — they're the items that decide whether your ADU can legally and physically work: design, engineering, permits, utility capacity, sewer, electrical, parking, fire safety, and site work. Miss them in your budget and you get the $50,000 surprise.

Utah ADU hidden-cost checklist

Permits, utility hookups, and site work — what to budget

The construction number is only part of an ADU budget. A serious Utah estimate separates design, permits, utilities, impact fees, site work, and construction so you can compare builder bids honestly instead of trusting one lump sum.

Permits. Any ADU that involves construction or remodeling requires the applicable building and trade permits (electrical, plumbing, mechanical), plus zoning review and inspections. Even when a space needs little or no remodeling, cities commonly require an ADU permit, a rental or business license, an owner-occupancy affidavit, or a recorded notice before you can legally rent it. The takeaway: there's a city process either way, and you can't skip it.

Utility hookups. A utility hookup is the work to connect your ADU to sewer, water, and electrical service. Detached units are the most exposed because they may need long trenching and new connections; even internal ADUs can need a panel upgrade or plumbing changes. Utah's detached-ADU law specifically lets a city deny a detached ADU where utilities lack adequate access or capacity — so confirming your sewer, water, and electrical situation early is one of the highest-value things you can do.

Site work. Detached ADUs cost more on sloped lots, in tight backyards, behind mature landscaping or hardscape, with long utility runs, or where retaining walls and drainage are needed. A flat lot with easy access and nearby utilities is a meaningfully cheaper project than a sloped one without.

For a full timeline of the permit and construction process, see our Utah ADU permit and build timeline guide.

What Utah's ADU laws mean for your project in 2026

Utah law has made ADUs easier to pursue — but it does not make every ADU cheap, automatic, or permit-free, and it treats internal and detached units very differently. The gap between what state law guarantees and what your city still controls is where most homeowner confusion lives.

Internal ADUs are protected statewide

An internal ADU (created inside your home's existing footprint and rented for 30+ days) is generally allowed as a permitted use in areas zoned primarily for residential use under state law (Utah Code §10-21-303, formerly §10-9a-530; see the Utah Office of the Property Rights Ombudsman summary) — but it's not automatic everywhere. That protection comes with conditions. By definition it applies only when the primary home is owner-occupied — meaning the owner lives in the detached single-family house as their primary residence — so it protects owner-occupants, not someone buying a property purely to rent out both units. Cities keep meaningful control too: they can prohibit internal ADUs on lots of 6,000 square feet or smaller, designate a limited share of residential land where they aren't allowed, require a design that doesn't change the home's appearance, require extra parking, require a rental license, ban short-term rentals, and prohibit renting an internal ADU that isn't in the owner's primary residence. The unit must still meet building, health, and fire codes.

Detached ADUs: new statewide rules take effect October 1, 2026

What it does not do is make detached ADUs automatic everywhere. Cities can still regulate size, height, setbacks (how far a structure must sit from your property lines), lot coverage, design, parking, owner occupancy, and rental terms — and they can deny a detached ADU where utilities lack capacity. Lots under 11,000 square feet remain up to local discretion, and some cities allow them on smaller lots. Our practical view: treat your city's adopted ordinance as the thing you actually build against, and verify it for your specific parcel before budgeting.

Short-term rentals — and minimum rental periods — are a separate question

Don't assume you can run your ADU as a nightly rental. Short-term rental (typically stays under 30 days) rules are set city by city and often differ by ADU type — and so do minimum rental periods. Internal ADUs are defined around long-term (30+ day) rental, but cities set their own limits, and the rules for detached units can be stricter still. Millcreek, for example, allows long-term rental of a detached ADU with the right approvals but prohibits short-term rental of detached units. If rental income — especially nightly rental — is part of your plan, confirm what's allowed for your ADU type in your city before anything else. It can be a dealbreaker.

Learn more: ADU rental income in Utah — what to expect

How Utah homeowners pay for an ADU

Most Utah ADUs are funded through home equity, renovation or construction financing, cash, family contributions, or — in a few cases — local programs. Financing is separate from feasibility: approval, rates, and terms are never guaranteed, so confirm what you qualify for before committing to a design.

Common paths include a HELOC or home equity loan, a cash-out refinance, a construction or renovation-to-permanent loan (some lenders underwrite these based on your home's expected value with the ADU completed — confirm current terms directly), and cash or family funds.

For a deeper look at all financing options, see our Utah ADU financing guide.

Is an ADU worth it in Utah — and when you shouldn't price one yet

For many Utah homeowners holding their property five or more years, an ADU can add usable space, optional rental income, or housing for family. But it is not a guaranteed return, and you'll see "adds 20–35% to your home value" claims online that nobody can promise for your property — value depends on legality, permits, build quality, your market, and how an appraiser treats it. Run your own numbers rather than trusting a headline percentage.

Some homeowners genuinely shouldn't price an ADU yet. Hold off and get a feasibility check first if:

• You're counting on short-term rental income but your city may not allow it.
• Your lot is too small or constrained for the detached plans you have in mind.
• You have an HOA or recorded restrictions you haven't checked.
• You can't easily replace required parking, or your utility capacity is unknown.
• Your budget is below the realistic range for the type you want.
• You're assuming you can build without permits or need guaranteed rental income or financing to make it work.

None of these means "never." They mean check before you spend on plans or bids. That's the safest, cheapest next step — and it's what a feasibility review is for.

How we put these numbers together

These are planning ranges, not quotes. We reconciled cost figures from multiple Utah ADU builders' published 2025–2026 cost guides, cross-checked them against national construction-cost references for component costs like foundations and framing, and present them as estimates because real costs swing with type, size, finish level, site conditions, and your city. The rules in this guide come from Utah state statute and individual city ordinance pages, and we note where a rule is city-specific versus statewide. Everything was last verified in June 2026. Laws, fees, and costs change — and exact permit, impact, and utility fees are set by each city and updated regularly — so confirm current details for your property before you commit money. When the answer depends on your specific parcel, we'd rather route you to a feasibility check than hand you a false-precision number.

Utah ADU cost FAQ

Sources we checked

• Utah Office of the Property Rights Ombudsman — internal-ADU guidance and statute references: commerce.utah.gov/propertyrights.
• Utah Code — §10-21-303 / §17-80-303 (internal ADUs), §10-21-304 (detached ADUs, effective Oct 1, 2026), §11-36a-202 (impact-fee exemption for internal ADUs): le.utah.gov.
• City and county pages — Salt Lake City Building Services; unincorporated Salt Lake County (Regional Development); Provo; Millcreek; South Jordan.
• Salt Lake City Community Reinvestment Agency — Backyard Keys ADU loan program terms: cra.slc.gov.
• Public 2025–2026 Utah cost and builder sources — used to triangulate the cost ranges shown as estimates.