In Orange County, a garage-conversion ADU typically takes 4–5 months from first site visit to move-in, permits included. A new detached ADU runs roughly 6–12 months depending on size and city. The construction itself is the predictable part — the permit counter is where timelines are won or lost, and it varies by city from about 4 weeks (Anaheim) to 10-plus (Newport Beach). Since January 2026, state law also puts a real clock on cities: 15 days to call your application complete, 60 days to decide. Here is the honest schedule, phase by phase.
01The real schedule, phase by phase
This is the garage-conversion timeline we actually run (a detached build follows the same shape with longer construction):
| Phase | When | What happens |
|---|---|---|
| 1 · Feasibility | Week 1 | Free on-site assessment — dimensions, slab and structure, utility points, parking, setbacks |
| 2 · Design & engineering | Weeks 2–4 | Floor plans, structural engineering, MEP layouts, Title-24 energy calcs |
| 3 · Permits | Weeks 5–12 | Full city submittal and plan-check corrections — the city decides this phase’s length |
| 4 · Construction | Weeks 13–24 | Demo → structural → electrical, plumbing & HVAC rough-in → insulation & drywall → finishes → exterior |
| 5 · Inspections | Final week | Final building, electrical and plumbing sign-offs → certificate of occupancy |
02The permit clock, city by city
Same project, different city, different month count. Typical plan-check timelines we see across Orange County:
| City | Typical plan check | The wrinkle |
|---|---|---|
| Anaheim | 4–6 weeks — fastest in OC | None to speak of; the counter knows ADUs cold |
| Tustin | 5–6 weeks | Case-by-case city — do the pre-application meeting |
| Costa Mesa | 5–7 weeks | Genuinely streamlined |
| Irvine | 6–8 weeks | HOA review runs on its own clock — start it in parallel |
| Huntington Beach | 6–8 weeks | Coastal-zone lots add a permit layer |
| Newport Beach | 8–10 weeks | Plus design review — the slowest, and the highest rents |
And the 2026 backstop: under SB 543, effective January 1, 2026, a city must determine your application is complete within 15 days and approve or deny within 60 days of completeness — miss those and the application can be deemed complete or approved. It is a legal backstop rather than a button you press, but it killed the old “resubmit everything” stall tactic.
03Where timelines actually die
Construction rarely blows the schedule. These do:
- Incomplete submittals. A missing survey or Title-24 report restarts the queue. This is the single biggest self-inflicted delay in the county, and it is entirely avoidable: submit everything, once.
- Correction-round ping-pong. Each round costs weeks. Answering every comment thoroughly the first time turns three rounds into one.
- The HOA with no deadline. Cities have legal clocks; HOAs do not. In Irvine especially, the HOA package must go out the same week as the city package or it becomes the critical path.
- Inspection queues. The build is done but the inspector is booked out. We schedule inspections ahead, not after.
- Change orders mid-build. Moving a kitchen wall in week 16 costs triple what deciding it in week 3 would have. Decisions made on paper are cheap; decisions made in framing are not.
04How we compress the schedule (honestly)
- One complete submittal — architecture, structural, Title-24, survey, all in the first package.
- Parallel tracks — HOA (where applicable) and city review run simultaneously, never in sequence.
- Pre-application meetings in case-by-case cities like Tustin — thirty minutes that remove the guesswork.
- All decisions before demo — finishes, fixtures and layout locked while changes are still free.
- Inspections booked early — the calendar is part of the build plan, not an afterthought.
What does not save weeks: promises. Any contractor quoting a dramatically shorter permit phase than the city actually runs is quoting hope. We would rather tell you Newport takes ten weeks and be right.
Want the timeline for your specific address and city? The free on-site assessment comes with one: book here or call (949) 374-7980.