There is no single Utah ADU rulebook. Every city sets its own, and they don't match.
Accessory dwelling units have become common enough in Utah that most cities along the Wasatch Front now have some kind of ordinance addressing them. What they don't have is a shared standard — size limits, setback requirements, parking requirements, occupancy rules and whether a unit can be rented to a non-family member all vary from one municipality to the next, and they've been revised repeatedly as demand has grown.
Whether the ADU can be detached or must attach to the main house. Maximum square footage, often expressed as a percentage of the main house's size. Minimum lot size to qualify at all. Parking requirements, which can be a real constraint on smaller in-fill lots. Owner-occupancy requirements, which some cities require and others don't.
Any specific figure — a size cap, a setback distance, a fee — that applies in one city may be wrong in the next one over, and these ordinances get updated. Stating one as a general fact would be more likely to mislead you than help you, so the honest answer is that it depends on your municipality.
Your city's planning or community development department publishes current accessory dwelling unit requirements, usually on the municipal website, and can confirm anything ambiguous by phone. That's the source worth trusting over a general answer from anyone else, including us.
Pull your city's current rules before design starts, not after a design is already drawn up. Designing first and checking compliance second is how projects end up needing an expensive redesign.
Beyond zoning, check whether your city and utility provider require a separate water or sewer connection for the ADU or allow it to share the main house's tap. That decision affects both the budget and the timeline, and it's set locally too.
Describe the project and we'll match you with a builder who works your city's process and your project's scale.
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