It depends on the ADU type and the city. As of October 2026, state law gives cities 60 days to act on a complete ADU application. In practice, state data from 2018 to 2022 showed Los Angeles County ADU permits averaging 147 days from application outside the Coastal Zone and 260 days inside it. Construction comes after the permit.
What are the phases of an ADU project?
- Lot check and feasibility. Zoning, setbacks, overlays, utilities and budget.
- Design and engineering. Plans, structural calculations, Title 24 energy documents and any soils report.
- Permit review. Submittal, plan check, corrections and permit issuance.
- Construction. Site work, foundation, framing, rough-in, inspections, finishes.
- Final inspection. City sign-off before the unit can be lived in.
See how we run each phase on our process page.
How long does ADU permit review take?
As of October 2026, state law sets two clocks: 15 business days for the city to say whether the application is complete, and 60 days from a complete application to approve or deny it when a home already exists on the lot. Each round of corrections and resubmittal adds time, which is why real-world numbers run longer.
The UC Berkeley Terner Center, using state data from 2018 to 2022, found Los Angeles County ADU applications averaged 260 days from application to permit inside the Coastal Zone and 147 days outside it. Since 2025, state law also applies a 60-day review period in the coastal zone.
Do pre-approved plans make permits faster?
They can. As of October 2026, some cities publish their own targets:
- Pasadena lists about 3 to 4 weeks of plan check for its ADU standard plan, after a 1 to 2 business-day completeness check. Details.
- Burbank lists a 30-business-day first review for its pre-approved ADU program, with a goal of permit issuance in 30 days. Details.
- Los Angeles says its Standard Plan Program reduces plan-check time, though LADBS still reviews site-specific items.
How long does ADU construction take?
It depends on the type and the site. A junior ADU or a garage conversion in good condition is usually the shortest build, because the structure exists. A new detached ADU takes longest, with a new foundation, frame, roof and utility runs. We do not quote a generic number here; we give you a written schedule with your price, based on your lot.
What slows an ADU project down?
- Incomplete plans that trigger several rounds of corrections
- Hillside, coastal, historic or fire-zone review
- Soils reports and engineering on sloped lots
- Utility upgrades, such as a larger electrical service
- Design changes after permit submittal
- Inspection scheduling and weather during foundation work
How can I keep my ADU on schedule?
- Check feasibility before design, so the plans match your lot's rules from the start.
- Lock the layout and finishes before submittal.
- Ask early about utility capacity.
- Consider a pre-approved plan if one fits your yard as drawn.
Sources, as of October 2026:
- California Department of Housing and Community Development, ADU Handbook (review deadlines).
- UC Berkeley Terner Center for Housing Innovation, analysis of ADU permitting in the Coastal Zone (state Annual Progress Report data, 2018 to 2022).
- City of Pasadena ADU Standard Plans Program; City of Burbank Preapproved ADU Program; LADBS ADU Standard Plan Program.