JADU vs ADU in Utah: what's the difference?

A JADU, or junior accessory dwelling unit, is a small living space carved out of an existing house — usually sharing a wall, and sometimes a bathroom, with the main home. A full ADU is a complete, independent dwelling with its own kitchen, bath, and entrance, often detached in the backyard. Utah ordinances more often say internal versus detached, but the practical split is the same: convert space you already have, or build something new.

What Utah actually calls a junior ADU

The term JADU comes out of California, where state law created a specific category: a very small unit converted from existing space inside a single-family home, with its own entrance, an efficiency kitchen, and often a bathroom shared with the main house. Plenty of Utah homeowners have picked up the term from podcasts and national articles, then gone looking for it in their city's code and found nothing.

In Utah, the dividing line in most ordinances is internal versus detached. An internal accessory dwelling unit is a dwelling inside the footprint of the existing house — a basement apartment, a converted upstairs, a unit behind the garage wall. A detached accessory dwelling unit is a separate building in the backyard. Some cities add a third flavor, an attached unit that shares a wall but was built new as an addition.

So when you read JADU vs ADU for a Utah property, translate it: the junior version is the internal unit, and the full version is the detached one. The distinction matters because Utah has moved to make internal units broadly available in single-family zones, while detached units remain largely a city-by-city decision. That gap is the single most important thing to understand before you start drawing plans.

How the two types differ in practice

Size is the obvious one. An internal unit is capped by the house you already own — you cannot carve out more square footage than the basement or the upper floor gives you, and many cities also cap internal units as a percentage of the home's floor area. A detached unit is capped instead by your yard: setbacks, lot coverage, and height limits for accessory structures, which are usually stricter than for the main house.

Kitchens and entrances are where the legal definitions get fussy. A full dwelling unit generally needs its own cooking facilities, bathroom, sleeping area, and exterior access. Junior-style units in other states are allowed a smaller efficiency kitchen and a shared bath. Utah cities vary on how much separation they require — a separate exterior door is almost always expected, and some ordinances want the internal connecting door to remain, or to be removed, depending on how they classify the unit.

Then there is the physical reality. An internal conversion means working inside an existing structure: egress windows, ceiling height, moisture in a basement, a panel that may not have room for another dwelling's load, and a sewer lateral sized for one household. A detached build means a foundation, a trench run for water, sewer, and power, and equipment access down the side of your house. Neither one is simply easier — they are different problems. Our walkthrough of how setbacks, slope, soil, and drainage shape a backyard ADU covers what the detached path demands from the dirt.

Owner-occupancy and the rules that change by address

Owner-occupancy requirements are common with accessory dwellings: the city asks that the property owner live in either the main house or the accessory unit, so the parcel does not become two rentals with an absentee landlord. Some Wasatch Front cities apply that condition, some have dropped it, and some apply it to detached units but not internal ones. There may be a recorded deed restriction or an annual registration tied to it.

Short-term rental rules are a separate layer and usually stricter. Many cities that allow a long-term accessory dwelling prohibit nightly rental of it outright. Parking is another: an extra off-street stall per unit is a common requirement, and on a quarter-acre lot that stall can land exactly where you wanted the building.

The honest summary is that your city decides, and two towns ten minutes apart on I-15 genuinely land in different places. Call the planning counter with your parcel number before you commit to a type. If you are curious why so many of these ordinances have been rewritten lately, Utah's housing demand and what it is doing to ADU rules explains the pressure behind the changes.

Which one fits your lot and your goals

An internal unit tends to make sense when you have usable basement square footage with decent ceiling height, a logical place for a separate entrance, and a goal that is modest: housing a parent, an adult child, or a long-term renter without changing the look of the property. It is typically the lower-disruption path in a city that limits detached buildings, and it is often the clearer path to approval.

A detached unit tends to make sense when the house is fully used, when privacy matters on both sides, when you want a real yard division between households, or when you want a building that reads as its own small home rather than a door on the side of yours. Detached units also tend to hold their appeal longer — a separate dwelling is a separate dwelling, whether the person in it is your mother this decade and a renter the next.

Cost drivers differ rather than one being universally cheaper. Internal conversions ride on existing structure but can run into egress, moisture, electrical capacity, and asbestos or knob-and-tube surprises in older Provo, Ogden, and Salt Lake homes. Detached builds carry foundation, utility trenching, and site work, but the work is predictable and nothing is hidden behind a wall. If you are weighing both at once, it is worth reading how many accessory dwellings one Utah property can legally hold, since some parcels can support an internal unit and a detached one.

At Cocoon Homes we build ADUs on site with a local Utah crew, and a typical project runs about four to six months covering architecture, city permitting, and construction. You can also walk through our model homes in Lehi — the 30 footer and the 400 and 450 square foot homes — to get an honest sense of how much living happens in a small footprint before you decide which path to take.

Frequently asked questions

Does Utah law recognize JADUs?

Not by that name in most places. JADU is a California term. Utah ordinances typically use internal, attached, and detached accessory dwelling unit instead. The internal category is the closest match to a junior ADU — a unit carved out of the existing house. Check your city's accessory dwelling section for the exact words it uses, since the definitions determine which rules apply to you.

Do I have to live on the property to have an ADU in Utah?

Sometimes. Owner-occupancy requirements are common but not universal, and some cities apply them only to certain unit types. Where they exist, the owner must live in either the main house or the accessory unit, and the city may record the condition against the property. Your city decides, so confirm with the planning department before you plan around renting both units.

Can a junior ADU have a full kitchen?

It depends on how your city defines the unit. Junior-style units elsewhere are limited to an efficiency kitchen, while a full accessory dwelling unit is expected to have complete cooking facilities. Utah cities vary on kitchen requirements for internal units. Since a kitchen is often what legally turns a bedroom suite into a dwelling, it is worth asking the planner directly before you order cabinets.

Is an internal ADU faster to permit than a detached one?

Often, yes. Internal units in single-family zones have a clearer path in many Utah cities, while detached units may require conditional use review, a minimum lot size, or a specific zoning district. That said, permitting speed depends on the city's workload and how complete your drawings are. An internal conversion with messy existing conditions can easily take longer than a straightforward backyard build.

Which adds more value, a JADU or a detached ADU?

A detached unit generally reads to buyers as a separate home, which tends to carry more appeal than a basement apartment with its own door. But value depends on your neighborhood, lot, and how well the unit is built. An internal conversion on a lot with no room for a backyard building can still be the smarter investment — the best unit is the one your parcel actually supports.

If you are trying to figure out which type your lot can support, reach out and we will talk through your parcel, your goals, and what a backyard unit would actually look like there. See more at mycocoonhomes.com.