Last reviewed: August 11, 2026. Planning ranges are based on contractor experience and are not city service guarantees. Rules and lender requirements vary by property, jurisdiction, and program.
For early planning, L Square estimates that a garage-conversion ADU may take about 4–5 months from the first site visit through final approvals, while a new detached ADU may take about 6–12 months. These are contractor planning ranges, not city service guarantees. Effective January 1, 2026, SB 543 generally gives a permitting agency 15 business days to provide a written completeness determination. For a completed ADU application on a lot with an existing dwelling, the agency generally has 60 days to approve or deny it, subject to the conditions and tolling rules in Government Code section 66317.
012026 planning schedule, phase by phase
This is an L Square planning estimate for a garage conversion; a detached build follows the same sequence with a property-specific schedule and typically requires more construction scope.
| 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 |
02L Square planning estimates by city
These ranges are L Square scheduling estimates from project experience, not published city service standards or guarantees. Actual review time depends on completeness, correction rounds, utilities, outside agencies, coastal review, and applicant-requested delays.
| City | Current timing note | Official resource |
|---|---|---|
| Anaheim | Confirm current timing with the jurisdiction. | City ADU information |
| Tustin | Confirm current timing with the jurisdiction. | City ADU information |
| Costa Mesa | Confirm current timing with the jurisdiction. | City ADU information |
| Irvine | Confirm current timing with the jurisdiction. | City permit information |
| Huntington Beach | Confirm current timing with the jurisdiction, including any coastal review. | City ADU summary |
| Newport Beach | Confirm current timing with the jurisdiction, including any coastal review. | City Building Division |
Under Government Code section 66317, a permitting agency generally has 15 business days to provide a written completeness determination; if it does not do so on time, the application is deemed complete. For a completed ADU application on a lot with an existing dwelling, the agency generally has 60 days from receipt to approve or deny it. Applicant-requested delays toll that period, and the statute includes conditions governing deemed approval.
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 a planning range for your specific address and city? A site assessment can identify the design, engineering, utility and review factors that may affect the schedule: book here or call (949) 374-7980.