Module 1 · Lesson 5
The ADU Process From Start to Finish
Feasibility, design, engineering, permits, construction, inspections — the full California ADU timeline explained stage by stage, with realistic durations.
Every ADU project — big or small, garage conversion or two-story build — moves through the same eight stages. Here's the map you'll follow for the rest of this course.
1. Property. Everything starts with your lot: its size, shape, slope, existing structures, and where the utilities are. Two neighbors on the same street can have completely different ADU options.
2. Feasibility. Before designing anything, you confirm what's actually possible: setbacks, height limits, easements, utility capacity, and any special conditions like fire zones or protected trees. Skipping this step is the #1 cause of wasted design money.
3. Design. Floor plans, elevations, and the decisions that shape daily life in the unit — where the kitchen goes, how light comes in, how the ADU relates to the main house.
4. Engineering. A structural engineer makes the design buildable: foundation details, framing sizes, shear walls. Energy calculations (Title 24) happen here too.
5. Permitting. Your plans go to the city for plan check. Reviewers send back corrections, your team responds, and after one or more rounds you get a permit. State law puts deadlines on how long cities can take.
6. Construction. Foundation, framing, rough plumbing and electrical, insulation, drywall, finishes. A typical ground-up ADU takes roughly 6–10 months of construction; garage conversions are often faster.
7. Inspections. City inspectors check the work at set milestones throughout construction — foundation, framing, insulation, and more. They're built into the process, not a surprise at the end.
8. Completion. The final inspection passes, you receive a certificate of occupancy, and the unit is legally ready to live in or rent.
How long does the whole thing take?
A realistic start-to-finish range for most projects is 10 to 18 months: roughly 2–4 months for design and engineering, 1–4 months for permitting depending on the city, and 5–10 months for construction. Garage conversions can run faster; hillside or complex projects run longer.
The rest of this course walks through each stage in order — the same order your real project will follow.
Key takeaways
- Every ADU follows the same path: property → feasibility → design → engineering → permitting → construction → inspections → completion.
- Feasibility comes before design — confirming what's possible first saves thousands in redrawn plans.
- Realistic total timeline: 10–18 months for most projects.
- Inspections happen throughout construction, not just at the end.