ADU Builder in St. George, UT | Guest Houses & Mother-in-Law Suites

In short

Inferno Construction builds ADUs and guest houses across St. George and Washington County: legally permitted accessory dwellings with a full kitchen, bathroom, and separate entrance. We handle the zoning, the utility connections, and the code that comes with a second dwelling, so the space can be lived in full time or rented.

Why Inferno

We handle the paperwork, you get the home

An ADU is a legal second home on your lot, and that is exactly what makes it valuable. Because it is permitted and built to dwelling code, it can house family, earn rental income, and add to what your property is worth. Getting there takes zoning, setbacks, parking, utilities, and inspections, and that is the part we take off your plate entirely.

We start with a free look at your lot. ADU rules across Southern Utah have opened up in recent years, and we build across St. George, Washington, Hurricane, Ivins, and the county, so we know the path to approval in each. You get a clear picture of the best ADU for your property before you spend anything on plans.

From there the build is a small, complete home: a full kitchen, a full bath, its own entrance, and often its own utility connections or submeters so you can track what a tenant uses. We coordinate the engineering, pull the permits, and manage the inspections, and we build it to match your house so it reads as part of the property and not as a rental bolted onto the back.

Free estimate See what is included

A two-story accessory dwelling framed and tied into the existing home.

20+Years of additions

What's included

A complete second home

An ADU is a full dwelling in miniature, held to the same code. The kitchen, the meters, and the permit are what make it legal to live in or rent.

Zoning & permits

We confirm what your lot allows, then handle the zoning, setbacks, engineering, permits, and inspections a second dwelling requires.

Full kitchen

A real kitchen with a range, sink, and appliances, plumbed and wired to code, which is part of what legally makes it a dwelling.

Full bath

A complete bathroom with proper venting and drainage, built to the same standard as the main house, not a half-finished add-on.

Separate entrance

Its own private entrance and, where required, its own address, so a tenant or family member comes and goes independently.

Utilities & metering

Water, sewer, and power run to the unit, with submeters or separate service so you can track usage.

Dedicated HVAC

Its own heating and cooling so the unit is comfortable and independent, sized for a Southern Utah summer.

Code-built envelope

Foundation, framing, insulation, and finishes built to dwelling code, so the ADU is financeable and insurable, not just habitable.

Exterior matching

Stucco, roof, windows, and trim matched to your home so the ADU reads as part of the property and protects your resale value.

ADU guide

Building an ADU in Southern Utah

More Southern Utah homeowners are adding a second home on their lot than ever. Here is how we plan an ADU that works for your family, your budget, and your property.

What we handle on every ADU

Lot check: ADU rules across Utah have opened up in recent years, so lots that did not qualify before often do now. We check yours for free on the first visit.
Plans & permits: Drawings, engineering, the permit submittal, and every inspection. We deal with the city so you do not have to.
Utilities: Water, sewer, power, and metering planned with the design and run to the unit, so it is ready to live in on day one.
Rental ready: If the ADU is for income, we design for tenants from the start and help you line up the paperwork to rent it.
One crew: Foundation to final walkthrough with one local team and one point of contact.

The site visit and written estimate are free, and we will tell you exactly what your lot can fit.

Types

Attached, detached, or internal ADU?

An internal ADU converts space inside your home, such as a basement or one wing, into a separate unit with its own kitchen, bath, and entrance. Because the structure already exists, it is often the fastest and most budget friendly way to add a unit.

An attached ADU is an addition built onto the house with its own entrance. A detached ADU is a separate small home in the backyard, with the most privacy of all. We build all three, because they draw on the same remodeling and additions crews.

Rental income

Building an ADU for rental income

A well built ADU can bring in steady long-term rental income while you keep your home. We confirm how your city lets you rent it before design, then help you line up the licensing so the unit is ready to lease when we hand over the keys.

Tenants pay for privacy, so we design for it: a separate entrance and path, sound separation from the main house, its own heating and cooling, laundry where it fits, and a small outdoor space of its own.

Family

Mother-in-law suites and multigenerational living

One of the most common reasons to build an ADU is family: aging parents moving closer, or grown kids getting a start. A full kitchen lets a parent live independently while staying close, which is a big part of what makes an ADU different from a casita.

Build for the long run. A zero-step entry, a curbless shower, wider doors, and blocking for grab bars are easy to include during construction. We also think about the connection between the two homes: close enough to help, private enough for everyone.

Lot planning

Will an ADU fit on my lot?

Often there is more room than people expect. Setbacks, parking, height, and where the utilities connect all shape the design, and a corner lot or an alley can open up even more options.

We check all of it during the free site visit, then sketch the unit on your actual lot so you can see the footprint, the parking, and the entrance before paying for full plans.

Budget

What drives the cost of an ADU

An ADU is a complete small home, and every lot is different, so we price it to yours. The biggest factors are the type (an internal conversion reuses the most existing structure), the size, how far utilities have to run, the foundation your soil needs, and the kitchen and bath finishes.

We quote after the site visit, in writing, so you can weigh the build against the rental income or family plans with real numbers in hand.

Timeline

How long does it take to build an ADU?

Permitting comes first, and we start that paperwork early and keep it moving so construction can begin as soon as possible.

Build time depends on the type. An internal conversion is mostly interior work and moves quickly. A detached unit adds trenching, a foundation, and a full exterior. We give you a realistic schedule for your specific project at the estimate.

What goes into it

Every detail, handled in house

One of our additions framed, sheathed, and closed in, windows and slider set, ready for the finishes inside. An ADU is built the same way, as a complete small home. Tap a marker to see what goes into it.

A hip-roofed addition sheathed in OSB with white-framed window openings and a sliding glass door, tied into the existing house on a concrete foundation.

Want this level of detail in your ADU?

Free estimate

How it works

From site visit to final walkthrough

Free site visit

We walk the lot, check what your city allows for an ADU, and talk through whether you want it for family, for rental income, or both.

Plans and permits

Drawings, engineering, and the zoning and permit submittal for a second dwelling, including parking and metering where your city requires it.

Build to dwelling code

Foundation, framing, a full kitchen and bath, utilities and HVAC, and finishes, all built and inspected to the code a dwelling has to meet.

Final walkthrough

We finish inside and out, confirm the unit passes its final inspections, and walk it with you so it is ready to live in or rent.

Real reviews

Homeowners on their projects

Two decades of building across St. George, and a 4.9 rating to show for it. Here is what a few of them had to say.

4.9on HomeAdvisor

20+Years local

They did a great job on my room addition. I wanted it to look like it was always part of the house even though the house is 23 years old. It turned out super nice and all the crew from Inferno were super.

Geoffrey L.Room Addition · HomeAdvisor

Questions

ADU & guest house FAQs

What is the difference between an ADU and a casita?

An ADU is a complete second home with a full kitchen, bath, and its own entrance, which means it can be lived in full time or rented. A casita is usually a detached guest suite with a bath and a wet bar, for family and guests. The build looks similar, and we help you choose the one that fits your plans and your lot before we design anything.

Can I build an ADU on my property?

There is a good chance you can. ADU rules across Utah have opened up in recent years, and St. George, Washington, Hurricane, Ivins, and the county each have their own path. We check your parcel during the free site visit and tell you exactly what your lot can fit before you spend anything on plans.

Can I rent out an ADU?

Yes, renting long term is one of the main reasons people build one. Each city has its own rental setup, so we confirm how yours works before design and help you line up the paperwork, so the unit is ready to lease when it is finished.

Does an ADU need its own utilities?

A full kitchen and bath need water, sewer, and electrical run to the unit. Metering options vary by city, and submeters are a simple way to track what a tenant uses. We plan the utility connections as part of the design so everything passes inspection the first time.

Will an ADU add value to my property?

A permitted, code-built ADU is an asset. It can generate rental income, house family, and add to what an appraiser and a buyer see. That is why we build every ADU to dwelling code and match it to your home.

Can I turn my basement or part of my house into an ADU?

Often, yes, and it is frequently the fastest way to add a unit. We add the kitchen, bath, separate entrance, and the safety details a dwelling needs, and handle the permits, so the space you already have becomes a second home.

Keep exploring

More ways we add space

Room Additions

Casitas

Detached Garages

ADU & guest house builder in St. George