ADU types
Garage Conversion ADUs
A garage already has a slab, walls and a roof. Whether those are good enough to live in, and where the cars go afterward, decides whether a conversion makes sense.
What we check in an existing garage
A garage conversion turns an attached or detached garage into a complete dwelling: kitchen, bathroom, sleeping area and its own entrance. It reuses the most expensive parts of a building, which is why it is often the lowest-cost route to an ADU.
The catch is that garages are not built as homes. Before design, we look at the building the way an inspector will.
- SlabCracks, settlement, slope toward the door, and whether there is room to build up an insulated floor
- FramingWall studs, headers and the roof structure, and whether they can take insulation, drywall and new openings
- RoofIts age and whether the attic can be insulated and ventilated
- HeightCeiling height once a new floor and insulation are added
- LocationDistance to property lines, the house and the sewer
- ParkingWhere the cars go once the garage is a home
Who a garage conversion suits
Owners whose garage is used for storage rather than cars, whose driveway can hold the required parking, and who want a separate unit without the cost of a new building. A single-level detached garage converted with a step-free entry can also work well for a parent. See in-law ADUs.
Attached or detached garage: a legal difference
An attached garage and a detached garage lead to different rule sets. Utah's definition of a primary dwelling includes a garage that is habitable space and connected to the house by a common wall. A converted attached garage can therefore be an internal ADU, which state law makes a permitted use in areas zoned primarily for residential use. A detached garage becomes a detached ADU, which follows each city's detached rules. See internal ADUs and detached ADUs.
Property considerations: setbacks and existing buildings
Many older detached garages sit close to a property line. Whether that is a problem depends on the city:
- Salt Lake City lets an existing accessory building converted to an ADU keep its existing setbacks. Any expansion must meet current setbacks.
- Murray and South Salt Lake only allow a conversion where the existing building meets the ADU setbacks.
- Millcreek allows a complying detached building to be converted if its setbacks are not further reduced and it meets or can meet building and fire codes. A legally established building that does not comply has a separate path through the Land Use Hearing Office.
- Holladay allows conversions of existing accessory buildings, including non-conforming ones, with standards.
- Sandy's detached ADU rules, adopted September 15, 2026, provide for converting legal accessory structures built before October 1, 2026.
State law is moving the same way. Utah Code 10-21-304, in effect since October 1, 2026, requires qualifying cities' detached ADU rules to include a process for converting a legally constructed accessory structure, subject to setbacks and building, health and fire codes.
Parking implications
Converting a garage removes covered parking, and cities notice. Utah law lets cities require replacement of garage or carport spaces when an internal ADU is created in them. Cottonwood Heights requires replacement of garage parking when an internal ADU is created there. Holladay requires displaced spaces to be replaced. Sandy says a garage conversion may not eliminate the required off-street stalls. Millcreek's ADU page says a conversion needs room for one more space for the ADU plus at least one covered stall to replace the garage. The practical question is whether the driveway and yard can hold the cars. See ADU parking requirements.
Design considerations
- The garage door opening: infilled with wall, windows or a glass entry, detailed so it no longer reads as a garage.
- Windows and egress: any sleeping room needs an egress window or door that meets the building code, and new windows bring the daylight garages lack.
- Layout: a one-car garage suits a studio; a two-car garage can hold a one-bedroom plan with a real kitchen.
- Accessibility: a garage is already at grade, which makes a step-free entry easier than in most ADU types.
Construction: insulation, plumbing, electrical and heat
Insulation goes into the walls, the ceiling or roof, and the floor. Garages are rarely insulated, and the energy code applies to the conversion. Plumbing is usually the biggest single task: a new sewer line from the kitchen and bathroom to the house's lateral, which means cutting the slab and trenching across the yard for a detached garage. Electrical service may need a new subpanel or a larger service at the house to carry a kitchen, heating and a water heater. See ADU electrical service. Heating and cooling for a small unit is often a ductless heat pump, sized to the insulated space.
Most cities we work in, including Millcreek, Murray, South Salt Lake, Sandy and Cottonwood Heights, prohibit a separate utility meter for an ADU, so the converted garage stays on the house's services. See ADU sewer and water.
Permitting a garage conversion
A conversion is a change of use from garage to dwelling, so it needs the city's ADU approval and a building permit with plans. Salt Lake City's standard plans page lists pre-approved designs that include a detached garage conversion. The city says a site review is still required and fees still apply. More in ADU permitting.
Cost considerations
The drivers are the condition of the slab and framing, the sewer run, electrical capacity, insulation and floor build-up, new windows and doors, replacement parking, finishes and fees. The garage conversion cost guide covers each one.
How a conversion project runs
We inspect the garage and check parking and setbacks first, then design, coordinate any engineering, prepare the applications, and manage construction through final inspection. Our feasibility review is where we tell you whether the garage is worth converting or whether a new building makes more sense.
Questions about garage conversion ADUs
Is a garage conversion cheaper than building a detached ADU?
Often, because the slab, walls and roof already exist. But garages are built to a lower standard than homes, so the savings depend on what the slab, framing and roof need. A garage that needs a new foundation or a new roof can close most of the gap.
Do I have to replace the parking I lose?
In most cities, yes. Utah law lets cities require replacement of garage or carport parking when an internal ADU is created there, and Cottonwood Heights, Holladay, Sandy and unincorporated Salt Lake County all have replacement rules. Millcreek's ADU page says a garage conversion needs room for an added ADU space plus at least one covered stall to replace the garage parking. Check your driveway before you check anything else.
Can I convert a detached garage that sits right on the property line?
Sometimes. Salt Lake City lets a converted accessory building keep its existing setbacks, although any expansion must meet current ones. Murray and South Salt Lake only allow a conversion where the existing building already meets the ADU setbacks. Millcreek and Holladay have separate paths for existing buildings that do not meet current standards.
Does the garage floor have to be raised?
Frequently. Garage slabs usually sit below the house floor and slope toward the door, and they rarely have insulation or a vapor barrier under them. Options include a new insulated floor system over the slab or a new slab, depending on ceiling height and the finished floor level you need at the doors.
Can I keep part of the garage as a garage?
Sometimes, if the building is large enough and the rules allow the combination. The garage part and the ADU part then need fire separation between them, and some cities count the whole building toward size limits. We check this against your city's code early.