The ADU Permitting Process Explained
Permitting is often the most confusing part of building an ADU. This guide breaks it down into clear steps so you know exactly what to expect.
Step-by-Step Timeline
| Step | Typical Duration | Cost |
|---|---|---|
| Pre-application research | 1–2 weeks | Free |
| Plan preparation | 2–4 weeks | $2,000–$8,000 |
| Plan submission | 1 day | $500–$2,000 filing fee |
| City plan review | 30–60 days | Included in filing fee |
| Permit issuance | 1–2 weeks | Varies by city |
| Construction | 8–16 weeks | Project dependent |
| Final inspection | 1–2 weeks | Included |
Timelines and costs vary significantly by jurisdiction.
Total timeline: 4–7 months from plan submission to move-in for most prefab ADU projects.
California's 60-Day Rule
California law requires cities to approve or deny ADU applications within 60 days of receiving a complete application. If they don't act within 60 days, your project is deemed approved. This is a powerful protection for homeowners.
Common Permitting Delays and How to Avoid Them
Incomplete applications — The number one cause of delays. Submit a complete application package with all required documents on the first try.
Setback issues — Know your property's required setbacks before designing your ADU. California allows 4-foot rear and side setbacks for ADUs, but some jurisdictions have additional requirements.
Utility capacity — Verify sewer, water, and electrical capacity early. Utility upgrades can add time and cost if not identified upfront.
HOA restrictions — California law limits HOA ability to block ADUs, but some associations still attempt to impose restrictions. Know your rights.
Pre-Engineered Plans Save Time
Using pre-engineered, state-approved plan sets dramatically simplifies the permitting process. These plans have already been reviewed for structural, electrical, plumbing, and energy compliance — reducing city review time significantly.
Permit Costs by City
Permit fees vary widely across California. Smaller cities may charge $2,000–$5,000 total, while larger cities like Los Angeles or San Francisco may charge $5,000–$15,000 or more. Many cities waive impact fees for ADUs under 750 square feet.
Working with Your City
Most California cities now have dedicated ADU staff or resources. Take advantage of free pre-application consultations to understand your specific requirements before investing in plans.