Utah has become one of the more ADU-friendly states in the West, making it easier for property owners to add a second unit without the lengthy approval processes that once slowed projects down. An ADU (accessory dwelling unit) is a secondary housing unit on the same residential lot as a primary home. You may hear them called granny flats, in-law suites, backyard cottages, or carriage houses. Landlords and homeowners build them to house family members, generate rental income, and add long-term property value.
What does it actually cost to build an ADU in Utah?
Cost is usually the first question, and the honest answer is: it depends heavily on the type of ADU and where in Utah you're building. That said, most Utah projects fall in a predictable range.
- Design fees: $5,000–$15,000 for architectural drawings, structural plans, and energy compliance documentation.
- Permit fees: $1,000–$5,000 depending on municipality and project scope.
- Construction: $80,000–$250,000 total, with basement and garage conversions on the low end and new detached structures on the high end.
What drives costs up? Site prep challenges (rocky soil, steep grade, limited access), custom design, high-end finishes, and the need for separate utility meters. What keeps costs down? Using an existing footprint like a basement or garage, staying within the lot's utility capacity, and choosing prefab or modular construction where local codes allow. Detached new-construction ADUs in Salt Lake City routinely hit the top of the range, while a straightforward basement conversion in a suburb like Murray or Taylorsville can come in under $100,000.
Some municipalities offer permit fee waivers or reductions for ADUs rented at affordable rates. Check with your city's planning division before budgeting, because these incentives can shave thousands off the early costs.
Types of ADUs allowed in Utah
Utah recognizes five primary configurations:
- Internal ADUs: Created within the existing home footprint, often from a basement or finished attic. Usually the most affordable option since the shell already exists.
- Attached ADUs: Built as an addition to the main structure, sharing at least one wall.
- Detached ADUs: Standalone structures in the rear or side yard. Most expensive to build, but they offer the most privacy and tend to command the highest rents.
- Garage conversions: Existing garage space converted into a habitable unit. Cost-effective because the structure is already there.
- ADUs in new construction: Designed and built alongside the primary home from the start, allowing for better integration and potential cost savings on shared work.
Statewide ADU legislation
Utah has made significant progress in reducing barriers to ADU construction. The most meaningful shift came on October 1, 2021, when the state reclassified internal and attached ADUs on single-family lots from conditional uses to permitted uses. Before that change, conditional use approvals could stretch past 90 days. That waiting period is gone for qualifying internal ADUs.
The legislation also converted existing conditional use approvals into permitted uses automatically, so owners who had already been through the old process didn't need to reapply. This reflects a broader state goal of increasing housing supply without requiring new land or infrastructure.
For the current statutory language, see Utah Code § 10-9a-530 (municipalities) and Utah Code § 17-27a-526 (counties).
Zoning eligibility and lot standards
Whether your property qualifies for an ADU depends on its zoning district. Utah allows ADUs in residential, commercial, downtown, gateway, and transit station zones, but each carries its own standards. Key factors include:
- Lot size: Minimum lot size requirements vary by zone and municipality.
- Setbacks: Detached ADUs must maintain specified distances from property lines. These differ across cities, so check with your local planning department.
- Building coverage: The combined footprint of the primary home and ADU generally can't exceed a set percentage of the lot.
- Height limits: ADU height is capped to maintain compatibility with adjacent properties.
Properties in historic districts carry additional requirements. Owners must obtain a Certificate of Appropriateness from the Historic Landmark Commission before construction, confirming the new unit won't compromise the district's architectural character.
ADU size, parking, and design rules
Utah ties size limits to the zone and lot size. Most cities cap ADU square footage at a percentage of the primary home's floor area or the total lot size. Your local planning department can give you the specific number that applies to your parcel.
Parking requirements are standard in most municipalities: expect to provide at least one additional off-street space for the ADU. Some cities relax this requirement for ADUs within a set distance of public transit.
On design, Utah Code limits how much local governments can mandate specific aesthetic elements. Cities can require that ADUs match the general character of the neighborhood, but they can't impose prescriptive design rules beyond what applies to primary residences. The goal is compatibility without unnecessary restrictions.
Permit requirements and owner occupancy
A building permit is required before any ADU work begins. Utah's framework includes a few consistent conditions across most jurisdictions:
Owner occupancy: The property owner must live in either the primary home or the ADU for at least six months of the year. A recorded legal covenant formalizing this requirement is part of the permit process.
Utility connections: The ADU must connect to utilities in line with local infrastructure standards. Separate metering may be required depending on the municipality.
Fire and safety codes: All building safety and fire code requirements must be satisfied before occupancy, including smoke detectors, egress windows, and proper ventilation.
Requirements vary by city, so confirm specifics with your local planning department. Salt Lake City Planning publishes ADU-specific guidance online.
Rental rules and short-term rentals
Long-term rentals are permitted under standard ADU rules, subject to the owner-occupancy requirement. Short-term rentals (platforms like Airbnb or Vrbo) are a different matter. Salt Lake City and other municipalities have separate licensing and zoning requirements for short-term rentals, and some neighborhoods or zones prohibit them entirely. Verify local rules before listing your ADU for short-term use, as operating without the proper license can result in fines and required removal of tenants.
HOA considerations
State law can override local zoning in many cases, but it doesn't automatically override HOA rules. If your property is subject to a homeowners association, review the CC&Rs before starting any ADU project. Some HOAs restrict or prohibit ADU construction, rental activity, or external modifications. If a conflict exists between state ADU law and your HOA's governing documents, the outcome depends on the specific language and may require legal review.
Protecting your investment with landlord insurance
Adding an ADU changes your property's risk profile in ways a standard homeowner's policy may not cover. If a rented unit isn't disclosed to your insurer and a claim arises, that claim can be denied. Before your ADU is occupied, review your coverage carefully. Exploring Utah landlord insurance options ensures both the primary home and the ADU are properly protected from day one.
Frequently asked questions
Are ADUs permitted by right in Utah?
Internal and attached ADUs on single-family lots became permitted uses statewide as of October 1, 2021, removing the conditional use approval requirement. Detached ADUs may still require additional review depending on the municipality.
Does Utah require owner occupancy for ADUs?
Yes. The property owner must reside in either the primary home or the ADU for at least six months per year, and a recorded covenant is required to formalize this condition.
Can I build an ADU in a historic district in Utah?
Yes, but you must first obtain a Certificate of Appropriateness from the Historic Landmark Commission. The review confirms the ADU is compatible with the district's architectural character.
What size can my ADU be in Utah?
Size limits depend on your municipality and zone. Most cities tie the maximum ADU size to a percentage of the primary home's square footage or the total lot area. Contact your local planning department for the specific limit that applies to your parcel.
Do garage conversions require a permit in Utah?
Yes. Any conversion of a garage or other existing structure into a habitable ADU requires a building permit and must meet current fire, safety, and building code standards.
Can I rent my ADU on a short-term basis?
Short-term rental rules vary by city. Salt Lake City and other municipalities have separate licensing requirements and zoning restrictions for short-term rentals. Verify local rules before listing your ADU on any short-term rental platform.
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