ADU Builder Lehi, Utah
ADU builder Lehi Utah homeowners call for a mother-in-law apartment, a rental unit, or a place for aging parents, and the first question is almost always the same: am I even allowed to build one on my lot? In Lehi the answer depends on your lot, your zoning, and whether your address falls inside the city’s ADU Restricted Area Map, which most homeowners have never heard of. Ironwood Custom Builders works that out before you spend money on design. From there we handle the Planning Division application, the building permit, and the build itself as one project, whether the unit goes into an existing basement, above an attached garage, or into a new detached structure in the back yard. It is the same coordinated process behind our custom homes and our ADU construction work across Utah County.
An ADU is also the one remodeling project where the paperwork can kill the job faster than the construction can. Owner-occupancy affidavits get recorded against your title, parking has to be provided, and the unit cannot be rented short-term. Getting that sequence wrong is expensive to unwind later.
What an ADU in Lehi Actually Is
Lehi defines an accessory dwelling unit as a separate housekeeping unit inside an existing single-family home, or in a separate building such as a space above a garage. To count as an ADU it needs all three of the following: a separate entrance, physical separation from the primary dwelling, and its own cooking, eating, sanitation, and sleeping facilities. Miss any one of those and it is a remodel, not an ADU, which changes the permitting path entirely.
There are two types, and they are regulated very differently.
Internal ADUs.
An internal unit goes inside the existing footprint of the home. In Lehi that most commonly means a basement apartment, a unit above an attached garage, or a self-contained wing to the side of the primary dwelling. Internal units carry the lighter permitting burden of the two, and there are no city impact fees. For most Lehi homes built during the 2000s and 2010s subdivision boom in Traverse Mountain, Holbrook Farms, and the west side, an unfinished basement is already the cheapest square footage available, which makes this the most common path we build.
Detached ADUs.
A detached unit is a separate building, typically a back yard cottage or a unit over a detached garage. Lehi’s detached ADU rules changed in July 2026 after the Utah Legislature passed a law requiring cities to allow detached ADUs and limiting what a city may regulate. Lehi amended Chapter 26 of its Development Code in response, which loosened the previous lot size threshold. Detached units still carry a one-time city impact fee that internal units do not, along with setback, height, access, and utility connection requirements. Because these numbers moved very recently, confirm the current figures for your lot with Lehi Planning before you commission drawings.
What an Ironwood ADU Build in Lehi Includes
Feasibility and zoning check first.
Before design, we confirm your lot qualifies: zoning district, lot size, frontage, whether your parcel sits in a Planned Unit Development, Planned Residential Development, Resort Community or Planned Community where ADUs are not allowed, and whether your address falls inside the ADU Restricted Area Map. This is the step most homeowners skip and the one that most often stops a project.
Planning Division application and owner-occupancy recording.
An ADU permit application goes through Lehi’s Planning Division, and an owner-occupancy affidavit gets recorded against your property with the Utah County Recorder. We prepare and manage both.
Building permit and inspections.
Separate from the Planning approval, every ADU needs a building permit from Lehi’s Building Division and has to meet the adopted building codes. Note that Utah moved to the 2024 International Building, Plumbing, Mechanical, Energy Conservation and Existing Building codes on July 1, 2026, with the Residential Code staying on the 2021 edition. We pull the permit and schedule every inspection.
A second kitchen that passes.
Cooking facilities are what legally make it a dwelling unit rather than a finished basement, and they bring plumbing, gas, electrical, and mechanical ventilation requirements with them. We rough in and build to code rather than adding a kitchenette after the fact.
A code-compliant bedroom.
A below-grade sleeping room needs a properly sized egress window with its own inspection sign-off. We handle the well excavation, the window, and the approval, the same as on our basement finishes.
Separate entrance and sound separation.
A private exterior entrance, fire and sound separation between the unit and the main house, and a layout that keeps both households functional. This is the difference between a rentable unit and a basement your tenant walks through your kitchen to reach.
Off-street parking.
Lehi requires off-street parking dedicated to the ADU. We lay that out on the site plan at design stage rather than discovering it at review.
Utilities.
Lehi does not allow separate utility connections for internal units, so the unit ties into the primary dwelling. Detached units have their own utility connection requirements. We coordinate all of it.
Project management. One Ironwood project manager runs the entire job and is your single point of contact from the first feasibility conversation to the final inspection.
What an ADU Costs in Lehi
Cost on a Lehi ADU is driven by a short list of things, and knowing them is more useful than a range you cannot rely on.
An internal unit built into an existing unfinished basement is the least expensive path, because the foundation, roof, and exterior walls already exist and there are no city impact fees. The cost sits in the second kitchen, the bathroom, the egress window, the separate entrance, and the fire and sound separation. A detached unit is materially more expensive: it is new construction with its own foundation, envelope, roof, and utility runs, plus a one-time city impact fee and, in some cases, an attached garage requirement.
Beyond that, the variables that move the number most are whether plumbing has to be re-routed or a new stack added, whether a new exterior entrance has to be cut into the foundation, how much grading and drainage the entrance and egress wells require, your finish tier, and whether the unit needs its own HVAC rather than an extension of the existing system.
The difference with Ironwood is that you get a complete itemized estimate for your specific lot and scope before any work begins, reflecting your foundation’s real condition rather than a per-square-foot average. Request a free estimate or use our ADU pricing tool to get a working number for your Lehi home. Our guide on what to ask an accessory dwelling unit contractor covers the questions worth asking before you sign with anyone.
Why Lehi Homeowners Choose Ironwood for an ADU
We check feasibility before you pay for design.
Lot size, zoning, frontage, HOA covenants, and the ADU Restricted Area Map all get confirmed first. Plenty of Lehi homeowners have paid an architect before finding out their parcel does not qualify.
Lehi City and Utah County permitting experience.
Lehi permits and inspects through Lehi City and Utah County, not Salt Lake County, and an ADU needs approvals from two separate city divisions plus a recorded document at the Utah County Recorder. Our project managers run that sequence regularly.
The second kitchen and the egress are the hard parts.
Most of what separates a legal ADU from a finished basement is plumbing, ventilation, egress, and fire separation. Those are build decisions, not finish decisions, and they have to be right before drywall.
One point of contact across every trade.
You work with one project manager across framing, plumbing, electrical, mechanical, and finishes, and through the permit process, rather than coordinating it yourself.
Award-winning craftsmanship.
Ironwood has been recognized across nearly every category of the Parade of Homes, and the crews that build our custom homes are the crews that build your ADU.
On-time, on-budget guarantee.
Our pre-construction process and on-time, on-budget guarantee mean you get a real number before you commit, and you hear from us immediately if anything changes.
How Your Lehi ADU Project Unfolds
- Free consultation and feasibility check. We visit your Lehi home, confirm your lot and zoning qualify, check the ADU Restricted Area Map, review any HOA covenants, and give you an initial estimate. Schedule yours.
- Design and scope lock. We finalize the unit layout, entrance location, kitchen and bath plan, parking, and utility approach, then lock a fixed scope and price.
- Planning Division application. We submit the ADU permit application and prepare the owner-occupancy affidavit for recording with the Utah County Recorder.
- Building permit. We submit for the building permit through Lehi’s Building Division and manage plan review corrections.
- Construction and rough-in. Framing, the separate entrance, egress window, plumbing and gas for the second kitchen, electrical, and mechanical, with inspections at each stage.
- Finishes and final inspection. Cabinetry, flooring, fixtures, and finish carpentry, then final inspection and certificate of occupancy. See what past clients say in our reviews.
Frequently Asked Questions
Are ADUs allowed in Lehi, Utah?
Yes, in owner-occupied single-family detached homes that meet the city’s lot and zoning requirements. Only one ADU is allowed per qualifying parcel. ADUs are not permitted in Planned Unit Developments, Planned Residential Developments, Resort Communities, Planned Communities, or on townhome, duplex, or other multi-family properties. Lehi also maintains an ADU Restricted Area Map where new internal ADUs are prohibited due to limited utility capacity, so your specific address matters. Ironwood confirms all of this for your lot before any design work begins.
Do I need a permit to build an ADU in Lehi?
Yes, and you need two separate approvals. An ADU permit application goes through Lehi’s Planning Division, and a building permit is required from the Building Division. An owner-occupancy affidavit also has to be recorded against your property with the Utah County Recorder. Ironwood prepares and manages all three as part of the project.
Can I rent my Lehi ADU on Airbnb?
No. Lehi does not allow an ADU to be occupied for terms shorter than 30 days. Short-term rentals require a separate license, and while a home can hold both a short-term rental approval and an ADU approval, the two cannot be operated at the same time. Long-term rental to a non-family tenant is permitted.
Does my tenant have to be a family member?
No. Lehi treats creating an ADU as a structural matter concerning alterations to a home, so occupants are not required to be related to the homeowner. You do have to continue living in the primary dwelling for as long as the ADU is occupied.
Can I build a detached ADU in my Lehi back yard?
Often yes, and the rules recently got more permissive. The Utah Legislature passed a law in 2026 requiring cities to allow detached ADUs and limiting what cities may regulate, and Lehi amended its Development Code in July 2026 in response. Detached units still have setback, height, access, utility connection, and lot size requirements, plus a one-time city impact fee that internal units do not carry. Because those figures changed very recently, confirm the current requirements for your lot with Lehi Planning at 385-201-1030 before commissioning drawings.
