Utah SB284 Explained: New ADU Rules for Homeowners

What Utah's SB284 Means If You Want a Backyard ADU

For years, the most frustrating part of building an accessory dwelling unit (ADU) in Utah wasn't the cost or the construction — it was finding out whether your city would even let you. Every town had its own rules, and plenty of them quietly said no to detached units in your backyard. Utah's SB284, passed in 2026, changed that.

Here's what the law actually does, in plain language, and what it still leaves up to your city.

The core change

SB284 requires most Utah cities — those with populations of 5,000 or more — to permit detached ADUs, not just internal ones. That's the key word: detached. Before this, a lot of cities only allowed "internal" ADUs (think a basement apartment carved out of your existing home). A separate backyard cottage or garage apartment was often off the table.

Under the new law, cities that don't already have a detached-ADU policy have to adopt one, with a deadline of October 2026. Lots of 11,000 square feet and up are squarely covered, though many cities allow detached units on smaller lots too.

There's one important limit: you generally get one ADU per lot — either internal or detached, not both.

What your city still controls

SB284 opened the door, but it didn't standardize everything. Cities still set the details that determine what you can actually build:

• Setbacks — how far the unit must sit from property lines
• Height limits — often a single story, sometimes more
• Parking — how many off-street spaces you need to add
• Owner-occupancy — whether you (the owner) must live in the main home or the ADU

These vary a lot from city to city, and they're being rewritten right now as cities scramble to meet the October 2026 deadline. That's exactly why checking your specific city matters before you spend a dollar on design.

We built a free, city-by-city Utah ADU ordinance tracker for this reason — it covers 34 Utah cities with what's allowed, lot minimums, height, owner-occupancy, and a link to each city's official source. If you're trying to figure out where your lot stands, that's the place to start.

Why this matters for your wallet

The shift to detached ADUs isn't just a permitting technicality — it changes the economics. A detached unit skips the structural headaches of carving living space out of your existing home (egress windows cut into the foundation, tying into existing HVAC and electrical, matching the rooflines on an addition). For a lot of homeowners, especially those building a rental, a detached ADU pencils out better than the alternatives.

If you want to understand the real numbers, we put together an honest breakdown of what an ADU actually costs in Utah, including a calculator that lets you ballpark your own project.

The bottom line

SB284 made backyard ADUs a real option for far more Utah homeowners than before. But "allowed by the state" and "allowed exactly how you want on your lot" are two different things — your city still fills in the blanks. Start by confirming your city's specific rules, get honest about the cost, and then talk to builders. You'll be a much sharper buyer for it.

Cocoon Homes builds detached ADUs across Utah — studio, one-bedroom, and two-bedroom layouts. If you're weighing a backyard unit, we're glad to help you think it through.