Building a Casita or ADU in Southern Utah: What to Know

A casita is one of the most useful things you can add to a Southern Utah home. Call it a casita, an accessory dwelling unit, a guest house, or a mother-in-law suite, the idea is the same: a small, self-contained living space separate from the main home. Here is how they work and what to consider if you want one.

Why People Build Them

Casitas earn their keep in several ways. They house out-of-state guests, who are plentiful in a place people love to visit. They give aging parents independence with proximity, a major driver in Southern Utah's retirement-heavy communities. They serve as a private home office or studio separated from family life. And depending on local rules, some owners use them for rental income. Many buyers want the option even if they are not sure which use comes first.

Attached vs. Detached

An attached casita shares a wall with the main home, often with its own exterior entrance, and is usually less expensive because it shares foundation, roof, and mechanical runs. A detached casita is a separate small building, more private and more flexible, but it carries its own foundation, roof, utility connections, and site work, so it costs more per square foot than the same space attached. Which one fits depends on your lot, your privacy goals, and your budget.

What It Costs

Small structures cost more per square foot than large ones, because the expensive rooms, a kitchen and a bathroom, are packed into a small footprint, and a detached unit duplicates foundation and roof. A casita is still a custom build, so it follows the same finish tiers as the main home, $305 per square foot at Standard, $385 at Premium, and $525 at Luxury, with the small-footprint premium on top and site work for a detached unit quoted separately. Our cost estimator at /cost-estimator can help you sketch a number, and a design conversation refines it.

The Rules That Govern ADUs

This is the part to check early, because it varies by jurisdiction. St. George, Washington, Hurricane, Ivins, Cedar City, and the counties each have their own rules on whether an ADU is allowed on a given lot, how large it can be, whether it can be rented, whether short-term rental is permitted, and parking and setback requirements. HOA design guidelines add another layer on top. Confirm what your specific lot allows before you design a casita, since the rules can decide its size and whether it can earn income.

Designing It Right

A good casita does not feel like a shed with a bed. The moves that make a small space feel generous are the same ones that make any desert home work: good natural light, a connection to a private patio or courtyard, deep overhangs against the sun, and a layout that does not waste a square foot. Designing the casita alongside the main home, rather than as an afterthought, lets the two share outdoor space and read as one composition.

Build It With the Main Home

If you know you want a casita, build it with the main home rather than later. Doing both at once shares mobilization, site work, and trade scheduling, and avoids tearing back into a finished landscape to add it on. It also lets the two structures be designed as a pair from the start. If you are building on your own land, our process at /build-on-your-land covers how we approach the whole site, casita included.