Thinking about building an ADU on your property in California? Whether you’re planning a backyard cottage for rental income or a private space for family, one of the first questions that comes up is how long the whole process actually takes. The truth is, timelines can vary quite a bit. From design and permits to construction and final inspection, several steps need to fall into place before your ADU is ready to use.
Quick Guide to Build an ADU in California
In this guide, we’ll break down each stage of the process, explain the average timeframes, and help you understand what might speed things up or slow things down. If you’re hoping to plan ahead or compare timelines between different types of ADUs, this post will give you a clear and realistic picture.
ADU Timeline: What to Expect
Building an ADU is not just about putting up walls and a roof it’s about planning, approvals, and coordination. Most homeowners in California can expect the process to take between 6 to 12 months from start to finish.
Some phases move quickly, while others especially permitting can require more patience depending on where you live. At Nestadu, we work closely with our clients to provide accurate timelines based on their property, ADU type, and city regulations.
Key Phases of the ADU Build Process in California
Here’s a closer look at the typical steps involved and how long each phase may take:
1. Planning and Design (2–4 Weeks)
Before construction starts, a lot of foundational work happens behind the scenes. This phase includes:
- A site assessment and feasibility review.
- Development of floor plans and 3D renderings.
- Design consultations and layout refinements.
The clearer your vision, the faster this part moves. At Nestadu, we help you make confident design decisions early to avoid delays later.
2. Permitting and City Approvals (1–3 Months)
Getting your plans approved by the local building department is often the most unpredictable step.
Here’s what’s typically involved:
- Submitting architectural drawings and site plans.
- Waiting for city review, comments, and approval.
- Adjusting plans (if needed) and resubmitting.
Factors that affect permitting time:
- Your city or county’s review capacity.
- Whether your property is in a fire, flood, or historic zone.
- How accurate and complete your plans are.
Some California cities now offer expedited ADU permitting, but others still have significant backlogs.
3. Site Preparation and Utility Planning (2–4 Weeks)
Once permits are issued, the site must be prepared for construction. This step includes:
- Clearing and grading the land.Build an ADU in California
- Utility trenching for water, sewer, and electricity.
- Demolition of existing structures, if needed.
This phase is often quick, but unexpected utility issues or soil conditions can create delays.
4. Construction Phase (4–6 Months)
With your site ready and permits in hand, construction begins. Here’s what’s typically included:
- Laying the foundation and pouring concrete.
- Framing, roofing, and exterior work.
- Installing plumbing, electrical, HVAC, and insulation.
- Interior finishes such as drywall, cabinetry, flooring, and paint.
If materials are ordered on time and inspections are passed smoothly, this phase flows steadily. But bad weather, inspection delays, or material shortages can stretch the schedule.
5. Final Inspections and Occupancy (1–2 Weeks)
The last phase is about making sure everything is safe, legal, and ready to live in.
Steps include:
- City inspections for plumbing, electrical, and structural work.
- Punch list fixes (minor touch-ups or corrections).
- Receiving a Certificate of Occupancy from the city.
Once approved, your ADU is officially complete and move-in ready.
Factors That Affect How Long It Takes to Build an ADU
The total time it takes depends on a few key elements:
Type of ADU
- Detached ADUs take the longest due to foundation and full build.
- Garage conversions are faster since the structure already exists.
- Junior ADUs (JADUs) usually take the least time since they involve converting part of the main home.
Your Location
Some cities like San Jose, Oakland, and Los Angeles offer dedicated ADU staff or expedited processes. Others may have longer queues or stricter zoning restrictions.
Permit Review Times
Every building department is different. Some issue permits in a few weeks, while others may take months.
Weather
Rain or extreme heat can delay foundation work, roofing, and inspections.
Material and Labor Availability
Ordering specialty finishes late or facing a shortage of skilled labor can push your schedule back.
Average Timelines by ADU Type
| ADU Type | Estimated Timeline |
| Detached ADU | 8–12 months |
| Garage Conversion | 4–6 months |
| Attached ADU | 6–9 months |
| Junior ADU (JADU) | 3–4 months |
These estimates assume a typical build without major delays. Working with an experienced team helps ensure your project stays closer to the lower end of these ranges.
How Nestadu Keeps Your ADU Project on Track
Nestadu has helped homeowners across California bring their ADU ideas to life on time and within expectations. Here’s how we support a smoother, more predictable timeline:
- Detailed planning from day one to avoid last-minute design changes.
- In-house designers and drafters that work closely with our build team.
- Permitting experts familiar with local codes and city workflows.
- Clear communication at every stage of the build.
We believe staying on schedule starts with staying informed. That’s why we provide realistic timelines, regular updates, and complete transparency.
Tips to Avoid Delays When Building an ADU
Want to avoid common pitfalls? These tips can help speed up your project:
- Hire a contractor who specializes in ADUs, not general remodels.
- Finalize your design choices before submitting for permits.
- Be proactive when the city asks for revisions or documents.
- Order windows, appliances, and fixtures early.
- Plan your build outside of the rainy season when possible.
These small decisions early on can save you weeks or even months in the long run.
Is It Worth the Wait?
While the ADU process can take time, the long-term benefits are hard to ignore:
- Monthly rental income to offset your mortgage.
- Added value to your property.
- Private living space for guests, parents, or adult children.
- Flexible future use whether as a home office, guest house, or short-term rental.
Most homeowners find that a few months of building is well worth the lasting value and function an ADU provides.
Final Thoughts
So, how long does it take to build an ADU in California? While each project is unique, most homeowners can expect a 6–12 month timeline from the first consultation to the final inspection. Some ADUs, like garage conversions or JADUs, can move faster, while detached ADUs may take longer due to permitting and construction scope.
The key to staying on track is working with a team that understands both the process and your local city’s requirements.
