ADU Construction in Cache Valley, Utah
A garage or basement conversion starts around $75,000. A detached ADU realistically runs $150,000 to $200,000. We publish our numbers before you call, so you know where you stand.
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Serving Cache Valley
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Conversion, Attached, Or Detached
These are genuinely different projects with different budgets, different permit paths, and different reasons to choose them. The right one usually falls out of one question: do you want the people living in that space to have access to your house, or not?
Garage or basement conversion
The most accessible entry point, because the structure already exists. A basement with plumbing already roughed in costs considerably less than a garage that needs everything run from scratch.
The tradeoff on a garage is that you lose the garage. In Cache Valley winters that is worth thinking about before you commit.
Attached
Shares at least one wall with your house, often with an interior door as well as its own entrance. You tie into existing utility connections, which saves on that side.
What it costs instead is engineering — integrating a new structure into an existing house means proper drawings for the framing, roofline and foundation tie-ins.
Detached
A standalone structure with its own foundation, framing, exterior and entrance. Full separation, which is almost always the right call for a rental.
In Cache Valley a realistic budget for a well-built, fully permitted mid-range detached unit is $150,000 to $200,000.
On cost it is close to a wash between attached and detached. Attached saves on utilities and spends it on engineering. Neither is meaningfully faster to build once construction starts.
Two Line Items That Surprise People
Utility connections
Running water, sewer and electrical from the street or the main house to a detached structure, before a single wall goes up. It varies with your lot and your soil.
Drawings and engineering
Architectural or engineered plans are required for the permit in most Cache Valley municipalities. It is a soft cost most homeowners do not anticipate, and it is not optional.
And a number to be suspicious of. If a contractor tells you they can build a full permitted ADU for $60,000 in 2026, they are cutting corners somewhere. Permits, fire blocking, waterproofing and proper utility connections are not optional line items — they are what make an ADU legal, safe and insurable.
Realistic Timelines
Conversion
From permit approval to completion.
Detached build
Depending on size, site conditions and the permit timeline.
Permit review
Before construction can begin. Longer for more complex projects.
What The Law Actually Says Now
Utah has moved on this twice in five years, and both moves went in your favor. HB 82 in 2021 made internal ADUs — a unit created inside the existing footprint of the home, like a basement apartment — a permitted use by right in most residential zones, which removed the conditional use approval that used to add months. Then SB 284, effective October 1, 2026, requires many Utah cities to allow a detached ADU as a permitted use on a lot of 11,000 square feet or larger that already has a single-family home on it, in a zone where single-family homes are allowed.
Two things get misread. The 2021 law covers internal units, not attached additions — an attached ADU adds new footprint and is generally reviewed under your city’s own rules. And the 2026 law is not universal: it turns on your city’s class and your county’s class rather than a flat population number, and the mandate only reaches lots of 11,000 square feet or more. Your city may well be more permissive than that state floor. Lot size, setbacks and parking still vary city to city, so the first move is always confirming your specific zone with your city — we do that before anyone pays for drawings.
Who issues it
Logan City has a dedicated ADU application through its Community Development Department. Providence, Smithfield and Hyrum route the building permit through the Cache County Building Department instead. Either way the process is the same: submit engineered plans, pay a fee based on construction value, wait for approval.
Setbacks
In most Cache Valley municipalities a detached ADU needs to sit at least four to six feet from rear and side property lines. It varies by city and by zone, and it is one of the things that decides whether the unit you have in mind actually fits.
Your HOA is separate
Read your CC&Rs before anything else. A city permit does not override HOA rules, and Cache Valley HOA restrictions sometimes go further than the city does. Utah law stops an HOA banning internal ADUs outright, but a detached unit can still be restricted.
Do not start construction before the permit is issued. That is how you end up with a stop work order, fines, and tearing out finished work so an inspector can see what is behind it. On every ADU we run we handle the whole permit process, schedule every inspection and meet the inspector on site — most of our clients never speak to the building department at all.
How To Decide, In Four Lines
Building a rental
Go detached. Full separation protects you and your tenant, and detached units tend to command higher rent.
Aging parents who value independence
Go detached, and put it as far from the main house as the lot allows.
Family who need to be connected
Go attached. Kids, or someone who needs care nearby — the interior door matters more than the privacy does.
Utility cost is the constraint
Attached usually makes more practical sense, because you are tying into connections that already exist.
The Value Question, Answered Carefully
National Association of Realtors data puts the property value increase from a well-built, fully permitted ADU at 20 to 35 percent, and in a tight market like Northern Utah that tends to sit at the higher end. ADU rents in Utah in 2026 are running $1,200 to $2,500 a month depending on size, location and finish.
The appraisal side has genuinely improved. Appraisers now look at comparable sales with ADUs, and increasingly apply an income-based approach that accounts for rental potential rather than counting square footage alone. Detached units tend to appraise slightly higher, because full independence is what buyers and appraisers respond to.
The one thing that undoes all of it is permitting. An unpermitted unit may not be recognized in an appraisal at all, and can create liability rather than value at resale. It is the reason we will not build one off the books.
Questions We Get About ADUs
Yes, always. An ADU is new construction. It needs a full permit, engineered plans and inspections at every phase — rough framing before walls close, rough electrical, plumbing and HVAC before insulation, insulation itself, then a final inspection before anyone can live in it.
Not on its own — an unfinished garage is not a dwelling unit. A garage conversion that turns it into a fully livable space with a kitchen, a bathroom and its own entrance can absolutely qualify, and it is one of the more cost-effective routes because the shell already exists.
Close to a wash. Attached saves on utility connections because you tie into what is already there, then spends it on the structural engineering needed to integrate the unit into your existing home. Detached carries $8,000 to $18,000 of utility work but no tie-in engineering.
Plan on two to four weeks minimum for review in most Cache Valley municipalities, and longer for complex projects. That is before construction starts, and it is why the front end of an ADU takes longer than people expect.
Possibly, for a detached unit. Utah law prevents an HOA banning internal ADUs outright, but external detached units can still be restricted by CC&Rs. Read them before you spend anything on drawings.
Start With A Conversation
Tell us your town, your lot, and who the space is for. We will tell you which permit desk it goes across, roughly what it costs, and whether what you have in mind actually fits your property.