Property feasibility
ADU Construction Timeline
An ADU schedule is a chain of steps, and several of them belong to someone else: the city, the utilities and the inspectors. Here are the phases, what stretches each one, and the review times cities actually publish.
"How long will it take?" is a fair question, and the honest answer at the start is that it depends on things nobody has checked yet. What we can do is lay out the phases in order, explain what makes each one longer or shorter, and point to the review timelines cities publish. We do not give durations in weeks or months before the property and the design are known.
The phases, in order
- Feasibility. Checking the city's rules, the lot, utilities and access. This decides whether the rest is worth doing.
- Design. Floor plan, elevations and site plan, with decisions on layout, materials and equipment.
- Engineering. Structural design, energy compliance and, on some lots, geotechnical or drainage work.
- Land use approval. The city's ADU review: a Planning application in Millcreek, an ADU Permit in Murray, a predevelopment review in South Salt Lake, an administrative Special Use Permit in Sandy, or a Planning Commission hearing for a detached ADU in Cottonwood Heights.
- Building permit. Plan review by building, fire and engineering staff, then corrections and issuance.
- Utility coordination. Provider letters, sewer and water connection approvals and, where needed, an electrical service upgrade.
- Construction. Site work and foundations, framing and roof, rough plumbing, electrical and mechanical, insulation, drywall, then finishes.
- Inspections and final. Inspections at each stage, then final approval and a certificate of occupancy.
- Rental licensing, if you rent. Several cities require a rental license, and Salt Lake City requires a zoning certificate before the certificate of occupancy for the ADU.
Our process page shows how we coordinate these as one project, and the ADU permit process covers the approvals in more detail.
Review times cities publish
Only some of the review steps have published targets, and all of them measure a single step, not the whole permit:
| City | What the city publishes |
|---|---|
| Millcreek | Building permit processing "may take 1-2 business days"; "up to 14 business days before an initial plan review"; revisions reviewed within up to 5 business days. Applications are abandoned after 180 days, and permits lapse if work does not start within 180 days. No Planning review time is published. |
| Salt Lake City | 14 business days for the first review of a one- or two-family residential project; responses to comments due within 180 days |
| Murray | Planning decision "approximately three (3) weeks" after a complete ADU application; the building permit is a separate application |
| South Salt Lake | If the predevelopment application is approved, a predevelopment meeting is scheduled within 30 days; complete building applications are reviewed within 15 business days |
| Cottonwood Heights | 5 to 7 business days to process a permit application after payment; the city strives to complete the first plan review within 7 business days. Detached ADUs go to the Planning Commission, with applications due by the month before the meeting |
| Holladay and Sandy | We found no published ADU review timelines |
Cottonwood Heights also notes that an ADU permit expires if the next step is not taken within six months of the last one, and since March 2, 2026 the city has not taken inspection requests on Fridays.
What stretches a schedule
- The approval route.An administrative review is shorter than a public hearing with a monthly agenda deadline.
- Incomplete plans.Each round of corrections restarts a review clock. Complete, coordinated drawings are the single biggest thing an owner and design team control.
- Engineering triggers.Sandy's checklist, for example, calls for engineer-stamped structural plans for an accessory building over 750 square feet or with walls over 10 feet. Hillside lots may need geotechnical reports.
- Utilities.Provider letters, capacity questions and service upgrades run on the utility's schedule. Rocky Mountain Power's own process starts with a call back within two business days, then site meetings, design and paperwork before work is scheduled.
- Site and season.Tight access slows every delivery, and foundations and exterior work are affected by winter conditions.
- Decisions.Late changes to layout, windows or finishes ripple through ordering and inspections.
- Hidden conditions.Conversions can uncover problems in footings, framing or wiring that need a fix before work continues.
What keeps it moving
Settling feasibility first, so design starts inside the real limits. Making selections before permit submittal. Getting utility questions answered early. In Salt Lake City, a pre-approved standard plan can remove some design work, though the city says a site review is still required and all fees still apply. If a detached ADU depends on the new state law, remember that Utah Code 10-21-304 took effect October 1, 2026, and cities may amend their codes around it.
Where to start
The fastest projects are the ones where the property was understood before design began. Work through Can I build an ADU?, then let us check the lot. Our ADU feasibility review identifies the approval route and the schedule risks for your property. To start, See What Your Property Can Support.
Questions about ADU timelines
How long does it take to build an ADU?
There is no honest single answer before the property and design are known. The approval route, the amount of engineering, utility work, site access, the season and how quickly decisions are made all change the schedule. We give a project schedule once feasibility and design have settled those questions, and we do not promise completion dates before then.
How long does the permit review take?
Some cities publish review targets. Millcreek says it may take up to 14 business days before an initial plan review, Salt Lake City targets 14 business days for a first review, South Salt Lake reviews complete building applications within 15 business days, and Murray's Planning decision comes approximately three weeks after a complete application. These are review steps, not the total time to a permit.
Is a garage conversion or basement ADU faster than a detached one?
Often there are fewer phases, since there is no new foundation or long utility trench. But existing buildings hide conditions, such as an undersized footing or old wiring, that only show up once work starts. The approval route in your city matters as much as the ADU type.
Can construction start before the building permit is issued?
No. Murray's application states that physical construction or occupancy cannot begin until the building permit is issued. In Sandy, a building permit alone does not let work begin; Public Utilities must also approve the project.