Why are Utah ADU cost ranges so wide?

Because “an ADU” covers everything from a basement using an existing slab to a ground-up backyard cottage. ADU type, existing conditions, utilities, site work, city rules, fees, and finish level all change the scope before a quote is even possible.

Is your estimate a contractor quote?

No. It’s a planning or feasibility estimate. A quote requires a builder to review a defined scope, plans and specs, allowances, and your actual site conditions.

Do your estimates include permits and impact fees?

We include them as allowances so the range reflects real all-in cost. The actual permit, plan-review, impact, and connection amounts have to be verified with your city, because they vary widely.

Are internal ADUs really exempt from impact fees in Utah?

Yes, with a caveat. Under Utah Code § 11-36a-202, impact fees are prohibited on the construction of an internal ADU within an existing primary dwelling. Permit, plan-review, inspection, and construction costs can still apply — it’s specifically impact fees that are exempt.

Do your estimates include utility upgrades?

Early estimates flag utility risk with a broad allowance, but the exact cost of trenching, connections, or panel/service upgrades usually needs a property-specific review.

Do you guarantee permit approval, rental income, or a higher home value?

No. Those depend on your property, your city, market conditions, and third-party decisions we don’t control. We’ll help you understand the factors; we won’t promise the outcome.

Why did my estimate change after a property review?

Because new facts showed up — utilities, structure condition, city rules, site access, plan complexity, fees, or a builder’s real scope. That’s the estimate getting more accurate, which is the point.

When should I actually talk to a builder?

Once you know your likely ADU type, your city’s constraints, the major utility and site risks, and whether the project is realistically in your budget. Walking in with those answers gets you better bids and fewer surprises.

Utah ADU Cost Methodology

By the Utah ADU Builders Editorial Team · Last verified: July 2026

Every Utah ADU cost range on this site is a planning estimate, not a contractor’s quote. We build each range from the ADU type, approximate size, your city’s rules and fees, likely utility and site conditions, and current Utah builder and vendor pricing — then we tell you how confident that number is. This page is most useful for homeowners deciding whether an ADU is worth pursuing, and least useful as a final budget. A reliable number requires a property-specific review, because your lot, city, utilities, and existing structure all move the number.

An ADU (accessory dwelling unit) is a self-contained second home on the same lot as a primary residence — a basement apartment, a garage conversion, an attached addition, or a detached backyard cottage.

A note on who we are. Utah ADU Builders is an independent Utah-focused ADU planning, feasibility, and builder-matching resource. We are not a city, a permit office, a law firm, a lender, an architect, an engineer, or a licensed contractor. We may earn a referral fee when homeowners request estimates or get connected with local professionals — and that compensation never changes how we explain Utah ADU rules, cost ranges, feasibility factors, or local permitting risks.

What we verified for this page

We checked	Against these sources
Utah state ADU law and the internal-ADU impact-fee rule	Utah Property Rights Ombudsman; Utah Code §§ 10-21-303 and 11-36a-202
City and county ADU rules used as examples	Official Salt Lake City, Salt Lake County, Millcreek, Murray, Draper, and Provo pages
How pre-approved city plans work	Salt Lake City Building Services (ADU Standard Plans)
Cost inputs and ADU-type assumptions	Published Utah builder/vendor pricing and national cost datasets adjusted to Utah, confidence-banded, with unconfirmed items flagged
What our estimates exclude and what we never guarantee	Stated plainly throughout this page

Full source links are at the bottom of the page.

The short version

Question	Straight answer
What is this page?	A plain-English explanation of our Utah ADU cost methodology — how we estimate ADU costs and how sure we are.
Is an estimate the same as a quote?	No. A quote needs a defined scope, plans, site facts, and a builder’s review.
What moves the number most?	ADU type, existing structure, utilities, site work, city fees, and finish level.
Are permits included?	We include them as allowances; actual permit and fee amounts must be verified locally.
Are impact fees included?	Internal ADUs built inside an existing home are exempt under Utah law; detached ADUs and new construction may owe local impact, connection, or utility fees.
Best next step	Check feasibility for your property before you compare builder bids.

What a cost estimate from us actually means

A planning estimate exists to save you time and money before you commit — not to replace a contractor’s bid. It helps you avoid chasing a path that’s clearly too expensive, legally tricky, or wrong for your property. The number gets more reliable as more facts about your lot and city get filled in.

The single biggest cause of “why are these numbers so different?” is that people compare three different things:

Building-only cost — Just labor and materials for the structure. It looks the lowest.

All-in project cost — Design, permits, site work, utility connections, construction, and standard finishes. This is the full project budget most homeowners have in mind when they ask what an ADU costs.

Turnkey / prefab base price — A bundled unit price that may include design and even permit submission, but often leaves out city permit fees and utility hookups.

Unless everyone is quoting the same scope, the numbers won’t match. When we publish a range, we’re aiming at all-in — and we say so.

Here’s the ladder every estimate climbs:

Stage	What it is
Planning range	A rough early range from ADU type and size
Feasibility-adjusted estimate	A property-aware estimate once we know your city and constraints
Quote-ready scope	A tighter estimate once site details and fees are checked
Contractor bid	A real, contractual number from a builder who has reviewed your project

How we build a Utah ADU cost range

We don’t pull a number from a single source, and we don’t claim a secret database of every Utah project. We work down a source hierarchy — property facts first, official rules second, real local pricing third — then attach a confidence level and flag anything we couldn’t confirm.

Priority	What we use	How it’s used
1	Your property facts	City, lot, ADU type, rough size, existing structure, photos
2	Utah state law	Baseline rules for internal and detached ADUs
3	City / county ordinance	Setbacks, lot minimums, parking, owner occupancy, rental rules
4	City & utility fee schedules	Permit, plan-review, impact, and connection allowances
5	Current Utah builder & vendor pricing	Real local construction and unit pricing, aggregated
6	National cost datasets, adjusted to Utah	Calibration only — never treated as a Utah quote
7	Editorial judgment	Applied only after the sourced inputs are clear

Where our cost inputs come from. For construction cost ranges specifically, we synthesize published Utah builder and vendor pricing, national construction-cost datasets (such as the Angi and HomeGuide cost data referenced on our cost guide) adjusted to the Utah market, and — for fees and utilities — official city and utility schedules. The specific builder, vendor, and dataset sources behind our current ranges are listed on our Utah ADU cost guide.

Our practical view: the honest first answer to “what will my ADU cost?” is a range with a confidence level, not a single number. Anyone who gives you an exact figure before seeing your lot, your city’s fees, and your utility situation is guessing — even if the guess is well-dressed.

What our estimates include — and what they don’t

A trustworthy estimate separates construction from design, permits, fees, utilities, site work, and contingency — and it’s clear about what it leaves out. The fastest way to mislead a homeowner is to show a low build number and stay quiet about everything that isn’t in it.

Usually included in our range	Not included until reviewed — or never guaranteed
Typical construction scope for the ADU type	×Furnishings and appliances beyond standard
Design & engineering allowance	×Landscaping beyond basic restoration
Permit & plan-review allowance	×Financing costs and interest
Standard finishes (low / mid / high assumption)	×Property-tax changes
A site-work and utility allowance (broad early on)	×HOA or CC&R approval and restrictions
Contingency for unknowns	×Permit approval — never guaranteed
	×Rental income — never guaranteed
	×Property value increase — never guaranteed
	×Final contractor bid pricing

One honest admission: 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. If the numbers don’t work for your situation, a good feasibility review should tell you that early — before you spend a dollar on plans.

Check ADU feasibility for your property.

See how these cost factors apply to your specific lot before you go further.

Check ADU feasibility for your property →

Why Utah ADU cost ranges are so wide

Two ADUs of the same square footage can cost tens of thousands of dollars apart, because one might reuse an existing basement while the other needs a new foundation, trenching, utility upgrades, and a full build. A wide first range is the honest answer when the expensive unknowns haven’t been checked yet.

The biggest swing factors:

Existing structure vs. new structure. Basement and garage projects lean on what’s already there. Detached ADUs behave like small houses.

Utility route and capacity. A utility hookup — connecting water, sewer, gas, and electrical to the unit — can move a budget fast. Salt Lake City’s own ADU Handbook flags drain grade and slope as a major up-front issue, and a long or complicated sewer trench can add thousands before any walls go up.

Site work and access. Slope, excavation, rocky soil, drainage, and equipment access all matter, and none of them show up in a square-footage estimate.

City fees. Permit and impact fees — one-time charges a city or utility collects to offset a new unit’s demand on roads, parks, water, and sewer — vary widely from city to city.

Finish level. A simple studio over a garage is not the same estimate as a detached two-bedroom with upgraded finishes.

How the estimate changes by ADU type

We don’t estimate a basement conversion, a garage conversion, a prefab unit, and a detached cottage with the same formula. Each has different cost drivers, different approval risks, and a different “biggest unknown.”

ADU type	Main cost drivers	Early-estimate confidence	Biggest unknown
Internal / basement	Egress, ceiling height, plumbing, HVAC, electrical, fire separation	Medium (with good photos)	Whether the space can legally and safely become a dwelling
Garage conversion	Existing slab and walls, insulation, mechanicals, parking replacement	Low–medium	Whether it triggers parking replacement or structural/utility upgrades
Attached addition	Foundation, envelope, roof tie-in, utilities, design	Low–medium	How it connects to the existing home and utilities
Prefab / modular	Unit price, foundation, delivery and set, hookups, site work, approvals	Medium for the unit; low all-in until the site is known	What the base price leaves out (often city permit fees and hookups)
Detached site-built	New foundation, structure, utilities, site work, setbacks, access	Low before a property review	Utility capacity, site work, city rules, and builder scope

A word on prefab and turnkey pricing, because it’s a common source of confusion. A base or “all-inclusive” prefab price may cover the unit, finishes, and even design, engineering, and permit submission — but it often excludes the city or county permit fees and the utility hookup costs, because those depend entirely on your property and city. Treat a prefab base price as the unit portion of your budget, not the whole project, until fees and hookups are measured for your lot.

How we handle Utah law, city rules, permits, and fees

Utah state law sets a floor, but it does not make every ADU type, rental use, fee, or detached structure automatically legal on every property. Our method separates what state law guarantees from what your city and lot still decide.

Internal ADUs

Internal ADUs get the strongest treatment under state law. An internal ADU is specifically defined as a unit created within the existing footprint of an owner-occupied, detached single-family home, for long-term rental of 30 consecutive days or longer. Where it qualifies, it is a permitted use in areas zoned primarily for residential use, and it must meet all applicable building, health, and fire codes (Utah Property Rights Ombudsman; Utah Code § 10-21-303).

Importantly, under Utah Code § 11-36a-202, constructing an internal ADU within an existing primary dwelling is exempt from impact fees. An impact fee is a one-time charge a city or utility levies on new construction to fund roads, parks, water, and sewer capacity; skipping it is a real savings. Standard permit, plan-review, inspection, and utility costs still apply — it’s specifically the impact fee that the statute exempts. Cities can still add reasonable conditions like parking requirements, owner-occupancy rules, and rental permits, so “exempt from impact fees” doesn’t mean “no fees at all.”

Detached ADUs

Detached ADUs are a different story. They can trigger impact fees, minimum lot sizes, setbacks (a setback is the required distance a structure must sit from your property lines), owner-occupancy rules (owner occupancy means you live in either the main home or the ADU), parking replacement, and — in some jurisdictions, for example unincorporated Salt Lake County — written confirmation from your water provider before a permit is issued. Detached-ADU rules are still shifting as Utah cities update their ordinances, so city-specific verification is essential.

How different can it be? Here are current detached-ADU lot-size minimums from five Utah jurisdictions:

Examples verified in July 2026 to illustrate how much rules differ — not a statewide standard. Your city’s current rules, lot minimum, and fees are what actually apply.

City / county	Minimum lot size for a detached ADU	A few local specifics	Source
Salt Lake City	No minimum lot size for an ADU where ADUs are permitted	Detached capped at 1,000 sq ft; 17 ft height (taller only with added setbacks); owner occupancy; recorded covenant. Zoning, setbacks, parking, and permit rules still apply.	SLC Code 21A.40.200
Salt Lake County (unincorporated)	7,000 sq ft (6,000 in the PC zone)	Written water-provider confirmation required before a permit; concrete slab required (unless above a garage); owner-occupancy affidavit.	Salt Lake County
Millcreek	8,000 sq ft	Detached max 1,000 sq ft; rear yard only; no separate utility meters — all utilities run from the main home.	Millcreek
Murray	10,000 sq ft	Max 20 ft and one story; 10 ft setbacks; capped at 50% of the primary home or 1,000 sq ft; a licensed contractor is required (no owner-builder).	Murray
Draper	12,000 sq ft	One detached ADU per lot; primary home must be owner-occupied; internal ADUs generally allowed on lots larger than 6,000 sq ft.	Draper

How city fees actually enter the estimate. We read fees from each city’s own schedule rather than guessing, because they diverge sharply — sometimes in opposite directions. In Provo, for example, a detached ADU requires impact fees for utility connections, parks, and emergency services, and must have its own separate utility meter. Nearby Millcreek does the reverse: it prohibits separate ADU meters and requires all utilities to run from the main home. Same state, opposite rules. That’s why we verify fees and utility requirements for your specific city and lot, and keep current fee amounts on our cost guide, where they can be updated as schedules change.

One more reality: a pre-approved plan is not a full approval. Salt Lake City, for example, maintains pre-approved ADU standard plans that can save time and design fees — but the city is explicit that a site-specific review is still required, all review and permitting fees still apply, and the city does not endorse any plan’s author or any specific builder. “Utah allows ADUs” and “this ADU is feasible on your lot” are two different sentences.

How reliable is your number?

An honest estimate should tell you how much to trust it. A rough planning range and a contractor’s written bid are not the same thing, and you shouldn’t make big decisions on the first when you need the fourth.

Level	What it is	Inputs behind it	Use it to…
1 — Planning range	A rough early range	ADU type, rough size, general area	Sanity-check whether an ADU is even in budget
2 — Feasibility-adjusted	A property-aware estimate	Address, city, photos, known constraints	Decide whether to keep going
3 — Quote-ready scope	A tighter, scoped estimate	Site details, plan/spec assumptions, fee checks	Prepare to request serious builder bids
4 — Contractor bid	A real, contractual number	A builder’s review of your scope, plans, and site	Make project, financing, and contract decisions

How we label uncertainty.

When a figure isn’t nailed down yet, we say so plainly instead of hiding it behind a single number. You’ll see labels like:

•Planning allowance — a reasonable placeholder we use before your details are known.
•Property-specific verification required — a cost that depends on your lot, city, or utilities and needs a real review.
•Not included until reviewed — items, like final fees or utility upgrades, that we deliberately leave out of an early range.

A number without a confidence level is a guess wearing a suit.

See what kind of ADU your property may support.

Find out which confidence level your estimate can realistically reach.

See what kind of ADU your property may support →

How often we update these ranges

ADU cost content goes stale quickly, so every number here has a visible verification date and a defined refresh process:

State law: Checked monthly during the legislative session, and at least quarterly otherwise (Utah Legislature, Utah Code, and the Utah Property Rights Ombudsman).

City ordinances and fee schedules: Reviewed quarterly for priority cities and around fiscal-year fee updates, using official city pages and published fee schedules.

Cost ranges: Reviewed quarterly using current Utah builder and vendor input, and calibrated against public labor and material data — which we use for context only, never as a direct Utah ADU quote.

Where we can’t confirm a current detail from an official published source, we say so rather than presenting a guess as a fact.

How to use this before you request estimates

The most useful next step is turning a broad range into a property-specific path. Before you compare builder bids, gather the facts that actually change feasibility and cost:

Gather this	Why it matters
Property address	Sets your city/county rules and fees
Photos of the space or backyard	Flags obvious feasibility issues early
The ADU type you want	Basement, garage, attached, prefab, or detached
Rough size	Scales the scope
Utility panel and route info	Flags electrical, sewer, and water risk
Basement ceiling height or garage dimensions	Critical for conversions
HOA / CC&R documents	Private rules may affect some projects — though for qualifying internal ADUs, Utah law can limit what an association restricts
Your goal	Rental, family housing, guests, office, or resale
Budget and timeline	Keeps the plan realistic

Request a Utah ADU feasibility review.

So the bids you gather are for a scope that\u2019s actually right for your lot.

Request a Utah ADU feasibility review →

Frequently asked questions

Sources

Utah Property Rights Ombudsman — Accessory Dwelling Units — propertyrights.utah.gov/find-the-law/legal-topics/adu/
Utah Code, Title 10, Chapter 21 (municipal ADUs, incl. § 10-21-303) and § 11-36a-202 (impact fees) — le.utah.gov/xcode/
Salt Lake City — ADU Standard Plans and Building Services — slc.gov/buildingservices/accessory-dwelling-unit-information/
Salt Lake City Code § 21A.40.200 (Accessory Dwelling Units) — codelibrary.amlegal.com/codes/saltlakecityut/latest/saltlakecity_ut/0-0-0-68737
Salt Lake County — Accessory Dwelling Units — saltlakecounty.gov/regional-development/planning-transportation/accessory-dwelling-units-adus/
Millcreek — Accessory Dwelling Units — millcreekut.gov/341/Accessory-Dwelling-Units-ADUs
Murray — Accessory Dwelling Units — murray.utah.gov/2168/ADUs---Accessory-Dwelling-Units
Draper — Accessory Dwelling Units — draperutah.gov/business-development/planning-and-development/accessory-dwelling-units-permits/
Provo — Accessory Dwelling Units — provo.gov/1367/Accessory-Dwelling-Units

Local rules and fees change. The examples above were verified in July 2026 and are provided to illustrate how much ADU rules and costs vary by city — always confirm current requirements for your specific property.

Utah ADU Builders is an independent Utah-focused ADU planning, feasibility, and builder-matching resource — not a city, HOA, law firm, lender, or licensed contractor. Nothing here is legal, financial, or construction advice.