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Patrice Peterson
★★★★★9 months ago
We hired Jimmy for a garage to ADU conversion project. The project was completed quickly, with diligent work from Jimmy's team, resulting in a finished product that exceeded our expectations!
How Long to Build an ADU in California: real timelines from our jobs
Last checked Oct 15, 2026
On our recent jobs, building a single ADU took about 4 to 6 months from ground breaking to finish. Plans and the city permit come first: once the city has a complete application, state law gives it 60 days to approve or deny it. Below are the steps, the state and Chino review times, and the dated timelines of seven ADUs we built. Questions about your lot: (951) 436-6568.
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The steps, in order
| Step | What happens | How long |
|---|---|---|
| 1. Lot check | We look at the yard or garage, setbacks, and where sewer, water and power will run | One visit |
| 2. Plans | A designer or architect draws the floor plan; an engineer adds the structure. Chino also offers free pre-approved detached ADU plans | Depends on the design; pre-approved plans skip most of it |
| 3. Completeness check | The city says whether the application is complete | 15 business days, or it is deemed complete (Gov. Code 66317) |
| 4. City decision | The city approves or denies a complete ADU application on a lot with an existing home | 60 days, or it is deemed approved (Gov. Code 66317) |
| 5. Chino plan check | The Building Division reviews the plans; corrections go back and forth | "4-5 weeks for the first review, and 1-2 weeks for the second and subsequent reviews" (city FAQ, Rev 1/15/2020) |
| 6. Fire district review | Chino Valley Fire District reviews the ADU; the city will not issue the permit until it approves | "7 to 10 business days", $452 review fee (fire district guideline) |
| 7. Build | Slab, framing, rough plumbing, electrical and HVAC, insulation, drywall, finishes, each inspected | About 4 to 6 months on most of our single ADUs (table below) |
| 8. Final and move-in | Final inspection and sign-off. An ADU cannot get its certificate of occupancy before the main house has one | Gov. Code 66328(a) |
Inspections in Chino: call before 3 pm for the next business day. A Chino building permit expires after 180 days without progress, with one 180-day extension.
Seven ADUs we built, and how long each took
These dates come from the progress posts on our Instagram, so they mark when a stage was posted, within a few weeks of when it happened. Construction time only; plans and permits came before.
| Job | Type | Started | Finished | About |
|---|---|---|---|---|
| Riverside, 800 sq ft | Detached ADU | Ground broken Oct 2024 | Finished Feb 2025 | 4 months |
| Santa Ana, Floral Park | Historic garage conversion | Ground broken Apr 2025 | Almost at final Aug 2025 | 4 months |
| Fontana | Multi-family ADU | Ready to pour Jul 2025 | Finish line Nov 2025 | 4 months |
| Fontana, 730 sq ft | Detached ADU, 2 bed, 2 bath | Week 3 in early Oct 2025 | Finished photos Mar 2026 | 6 months |
| San Clemente, 700 sq ft | ADU above the garage | Ground broken Jul 2025 | Completed Jan 2026 | 6 months |
| Rancho Cucamonga | Custom ADU | Slab poured Nov 2024 | Counters in Jul 2025 | 8 months |
| San Clemente | Duplex ADU, two units | Kicked off Aug 2025 | Final photos Jul 2026 | 11 months |
What makes an ADU take longer
Waiting on the city. The clock you control least is plan check. One of our clients, who turned an 1,100 sq ft garage into a two-bed casita, wrote: "While we waited quite some time for the city, Jimmy and his crews moved quickly with things once we had the green light." A complete first submittal is the best way to shorten that wait.
Custom details. The Rancho Cucamonga unit took about 8 months because of what went into it: a pocket corner door, kerf white oak jambs and doors, a recessed baseboard, a custom concrete floor and custom cabinets.
Two stories or two units. The San Clemente duplex ADU had a second story and two kitchens, and ran about 11 months from kick-off to final photos.
Special review. A historic district adds a review. In Santa Ana's Floral Park we coordinated with the historic department from day one, which kept that conversion on time.
What makes it faster
Reusing a structure. A garage conversion keeps the slab, walls and roof, so there is less to build; one client wrote that their garage-to-ADU project "was completed quickly." A city's pre-approved plan can also shorten review, and Chino offers them for detached ADUs (details on our Chino ADU rules page).
Sources
Every rule on this page comes from these, opened and read on the date shown.
- Government Code 66317 (ADU permit clock) and 66328 (certificate of occupancy), leginfo, read Oct 15 2026
- City of Chino Building Division FAQ, Rev 1/15/2020, read Oct 15 2026
- Chino Valley Fire District ADU submittal guideline, undated, read Oct 15 2026
- City of Chino, Building Division page, read Oct 15 2026
- Job dates: our own progress posts, @jo__construction, Sep 2024 to Jul 2026
This guide supports our ADU builder page, where you can see every ADU we have built. Or go back to the J.O. Construction home page.
What clients sayReal words from Google, unedited.
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Antonio Reyes
★★★★★a year ago
Thank you Jimmy for taking on our project for our ADU build. It was a pleasure from beginning to end to work with you guys. Always very transparent and there to answer any phone calls or questions.
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Bert MTZ
★★★★★2 years ago
ADU 730sf in Fontana, two bedrooms two bathrooms, complete kitchen. … Provided a good service and choices with the option of getting upgrades. Communication was key and Jimmy made it easy to reach out and listen to concerns or changes.
Questions owners ask us
How long does the city take to approve an ADU?
State law gives a city 60 days from a complete application to approve or deny an ADU on a lot with an existing home, and 15 business days to say whether the application is complete. Corrections restart parts of that, so a complete first submittal matters.
Want a timeline for your lot?
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