Utah ADUs went from a niche side project to a mainstream housing category in the span of about three years. House Bill 82 in 2021 forced every city in the state to allow internal ADUs in any residential zone. Several follow-on laws have tightened the rules further. The result: a lot of homeowners are suddenly thinking about adding an apartment to their house and running into the question of who actually does the engineering.
What HB 82 actually says (the short version)
Three things to know:
- Internal ADUs are now a "permitted use" in any single-family residential zone in Utah. That means the city can't force you through a conditional use process or a public hearing. They can still require a building permit.
- Cities can still impose reasonable requirements:permits, owner-occupancy, one extra off-street parking space, and they can exclude up to 25% of their residential zones from the rule. They can enforce setbacks, height limits, and the building code.
- Attached and detached ADUs still depend on local ordinance. Some Davis and Weber County cities allow them, some restrict them, some require a separate permit pathway. We know which is which for the cities we work in.
For the homeowner-friendly walk-through, see our blog post — A Plain-English Guide to Utah's HB 82 ADU Law.
What we engineer on a typical ADU
- Foundation design — new footings for detached or attached units, evaluation of existing slab for garage conversions, underpinning or pier upgrades when needed.
- Floor and roof framing — joist sizing, beam locations, headers over new openings, ridge and rafter design.
- Lateral system — shear walls, hold-downs, anchor bolts. Critical on the Wasatch Front because of the seismic story.
- Snow and seismic loading — using the actual ground snow load for your jurisdiction (43 psf base in most of Davis and Weber, more on benches and foothills) and the right seismic Site Class for your soil conditions.
- Existing-structure evaluation — for internal and attached ADUs, can the existing house take the new loads? Often yes, but the answer matters and needs to be in writing.
- Plan-check support — if the building department has comments, we respond. Always included.
Garage conversions: the most common ADU we see
Converting an attached garage into a livable ADU is the single most popular ADU strategy in Davis County right now, and it's almost always more involved than homeowners expect. Garage slabs often aren't insulated, the floor is sloped to a drain, the framing wasn't designed for the loads of a heated living space, and the lateral system wasn't designed assuming someone would sleep there. Most garage conversions need: a new sub-floor system (sometimes), header upgrades where the garage door used to be, evaluation of the existing roof for snow loads at full residential occupancy, and a fire-separation review.
We've seen enough garage conversions in Layton, Clearfield, and Kaysville to know what the local plan reviewers look for. The engineering scope is usually $1,500–$3,000 depending on size and complexity, and the result is a stamped set that gets approved on the first plan check.
City-specific notes
A few of the things that catch homeowners off guard, by city:
- Syracuse: ADUs require a permit, and there's a minimum total floor area requirement that surprises some owners building very small units. More on Syracuse →
- Layton: ADUs are allowed in any SFR zone, but short-term rental of an ADU is prohibited. Permit required. More on Layton →
- Kaysville: Detached ADUs face stricter setback and lot-coverage rules than internal. Worth a phone call to planning before you commit to a layout. More on Kaysville →
- Ogden: A historically permissive city for ADUs; internal and detached both common. More on Ogden →
How we'd start your ADU project
Send us the basics: your address, what you're hoping to build (internal, garage conversion, detached, attached), and any drawings or layouts you already have. We'll come back the same day with a fixed fee for the engineering scope, an honest take on what your jurisdiction is going to require, and a timeline. From there it's usually 1–3 weeks to a stamped set in your hands.