Utah ADU Cost by City: What Actually Changes Your Budget (2026)

First, the terms (30 seconds)

Four words make the rest of this page clear.

ADU (accessory dwelling unit):

a second, self-contained home on the same lot as your main house — its own kitchen, bathroom, sleeping and living space.

Internal ADU (IADU):

an ADU created inside your existing home’s footprint, most often a basement apartment. Utah’s strongest ADU protection applies specifically to internal ADUs — but with real limits: the protection covers a unit within a detached single-family home that the owner occupies as a primary residence, offered as a long-term rental of 30 days or more. If you’re in a townhome, an attached unit, a non-owner-occupied home, or you want nightly rentals, that state protection may not apply to you.

Detached ADU (DADU):

a separate building in your yard — a backyard cottage or a unit above a detached garage. Usually the most expensive and the most city-dependent.

Garage conversion:

turning an existing garage into a livable unit. Cheaper because the shell exists — but it can trigger a parking rule.

Two more you’ll see below: an impact fee is a one-time charge a city collects to help pay for the added demand a new unit puts on roads, parks, sewer, and water; a utility hookup (or connection) is the cost of physically running and metering water, sewer, and power to the unit.

Utah ADU cost by city: the comparison table

Here’s what actually changes by city. We hold construction cost roughly steady (the dollars are in the by-type table below) and compare the city-controlled variables, because those are the parts that genuinely differ. Cells marked “Verify” are ones we could not confirm from an official published source at last review — always confirm your own city’s current ordinance and fee schedule before you budget.

How to read “cost pressure”: it reflects impact-fee exposure, parking and lot-size friction, rental and owner-occupancy limits, and design or historic review — not a guaranteed dollar amount.

Two things that apply everywhere in Utah: internal ADUs are a permitted use in most residential zones statewide and are exempt from impact fees (a big reason basement conversions cost less); and detached-ADU rules are changing in 2026 under SB 284 (see the next section), so several cities are actively updating their codes right now.

“Verify” cells = could not confirm from an official published source at last review. Confirm with your city’s planning department before budgeting.

Which Utah cities allow detached ADUs — and what SB 284 changes in 2026

Internal ADUs (like a basement apartment inside your home) are already allowed by right in most Utah residential zones. Detached backyard units have historically been up to each city — some allowed them, many didn’t, and several only allowed them on very large lots. A 2026 state law, SB 284, changes that.

What SB 284 does not do

• It doesn’t eliminate permits, fees, or local design and utility standards.
• It doesn’t override your HOA. Under Utah’s Community Association Act, an HOA generally cannot enforce a blanket ban on internal ADUs, but an HOA can prohibit detached ADUs even where the city allows them (Utah Department of Commerce). If you’re in an HOA, read your governing documents before you plan a backyard unit.
• It doesn’t guarantee your lot qualifies, that approval is automatic, or that a detached unit is the right financial choice.

Where do city costs run higher — and where do they run lower?

Cities push the city-controlled portion up when they add impact fees, mandatory parking you don’t already have, or design review — and Utah’s resort and historic areas are where that stacks up most. Cities keep it lower when they exempt internal ADUs from impact fees (all of Utah, by law), waive parking near transit, or charge little for permits. Just remember this is a small share of the total.

We’re deliberately not naming a single “cheapest city,” because a lower fee schedule doesn’t make a project cheaper if your lot needs long utility trenching or can’t fit a required parking stall. Your lot usually decides more than your ZIP code.

Is your property likely a fit before you price it out?

Before you ask builders for quotes, answer the questions that change the cost — and the feasibility — the most. If several of these are unknowns, that’s your signal to check feasibility first rather than collect random bids.

Can prefab or standard plans lower the cost?

Prefab, modular, and pre-approved standard plans can shorten the design-and-permit stage and make unit pricing clearer — but they don’t erase site work, foundation, utilities, delivery/access, permits, or city fees. A low “unit price” is not a finished-project price.

Prefab helps most when your lot has good access and simple utility connections; it helps least on tight, sloped, or hard-to-reach lots where the expensive part is the site, not the box.

The lowest-risk starting point for most Utah homeowners

The lowest-risk path is usually the ADU type that reuses the most of what you already have while still meeting your city’s rules. For many people that means checking internal/basement feasibility first, then a garage conversion, then a detached or prefab build if the lot, utilities, parking, and budget support it.

Your next step: a city-aware cost and feasibility check

The right first move isn’t collecting five random quotes — it’s understanding what your city allows, whether your lot qualifies, and which build path fits your budget and goal. From there, an estimate actually means something.