Utah Accessory Dwelling Unit and Basement Apartment Rules

An internal accessory dwelling unit is a separate dwelling unit created within a primary dwelling. It typically includes independent living, sleeping, cooking, and sanitation facilities. A finished basement with a bedroom and wet bar is not necessarily an approved ADU. Legal status depends on use, configuration, permits, and local requirements.

State law limits how municipalities and counties may restrict internal ADUs, but two parallel statutes apply depending on where the property sits: Utah Code 10-21-303 governs property inside a city, and Utah Code 17-80-303 governs property in the unincorporated county. Local governments still retain authority over building safety and several operational requirements. Cities and counties may require registration, owner occupancy, parking, separate entrances, address identification, unit-size or lot-size conditions, utility-capacity limits, impact fees, or proof that the property is not used as a short-term rental. State law sets boundaries on what local governments may prohibit, but local permitting and operating requirements still vary significantly — verify the current ordinance for the specific city or county and zoning district before relying on it.

A detached ADU — a separate structure, not built within or attached to the primary dwelling — is governed by its own statute, Utah Code 10-21-304, not the internal-ADU rules above. This law takes effect October 1, 2026. It applies only in a 'specified municipality' (generally larger cities, not every Utah city or town), and it does not apply to unincorporated county land at all. Where it does apply, it generally covers lots of 11,000 square feet or larger with an existing single-family home — but a qualifying lot in a covered city still does not guarantee an approved detached ADU. Short-term-rental treatment also differs by type: cities may prohibit renting an internal ADU for fewer than 30 consecutive days, versus fewer than 90 consecutive days for a detached ADU.

• Require the owner to live in the primary home or the detached ADU
• Set on-site parking requirements (up to two spaces for larger units, one for smaller units)
• Control size, height, setbacks, and design consistency with the main home
• Require a permitting process, including for converting an existing accessory structure
• Prohibit renting the detached ADU for fewer than 90 consecutive days
• Block a detached ADU where sewer, water, electrical, or storm-water capacity is insufficient

• Ask for the original permit and certificate or approval.
• Confirm zoning and current registration.
• Verify owner-occupancy requirements.
• Review parking and entrance compliance.
• Check egress, fire separation, smoke and carbon-monoxide protection.
• Confirm electrical, plumbing, heating, and kitchen permits.
• Review the existing lease and security deposit.
• Confirm whether utilities are shared or separately metered.

Projected ADU income may help a buyer, but lenders vary in how they count rent. Legal status, appraiser treatment, lease history, and loan program rules matter. Do not base affordability on full rent without budgeting vacancy, utilities, maintenance, turnover, insurance, taxes, and the possibility that the unit cannot be rented as planned.

Permission for an internal or detached ADU does not automatically authorize nightly or short-term rental use. Local ordinances, business licenses, owner occupancy, HOA restrictions, and zoning can prohibit or limit short stays, and the minimum stay a city can enforce differs by ADU type — see the detached-ADU section above.

Before construction, obtain a zoning review and permit path. The cost may include egress windows, fire separation, electrical upgrades, heating changes, parking work, utility modifications, design fees, and impact-related requirements. A cheap unpermitted conversion can become expensive when the owner sells, refinances, insures the property, or responds to a complaint.

An internal ADU or basement apartment is one common form of house hacking — living in part of a property while renting the rest to help offset the cost of housing yourself. A detached ADU can create the same kind of opportunity on a qualifying lot. Either way, legal use and how a lender treats the rental income are two separate questions, and both need to be verified before counting on that rent. The House-Hack Net Housing Cost Calculator can help estimate the numbers once the unit's legal status is confirmed.

An ADU can improve affordability and property flexibility, but only if the unit is legally usable and financially realistic. Verify the local approval, physical code compliance, rental restrictions, and operating costs before paying an income-property premium.