Getting permits is often the most confusing part of building an ADU. But understanding the process upfront saves time, money, and frustration. Here is exactly what to expect.
Typical Permit Timeline
| Phase | Duration | What Happens |
|---|---|---|
| Pre-Application | 1-2 weeks | Research zoning, meet with planning staff, confirm ADU eligibility |
| Design & Plans | 4-8 weeks | Architect creates construction documents; engineering if needed |
| Plan Submission | 1 day | Submit complete plan set to building department |
| Plan Review | 4-12 weeks | City reviews for code compliance; may request corrections |
| Permit Issuance | 1-2 weeks | Pay fees, receive building permit |
| Construction | 3-12 months | Build with required inspections at each phase |
| Final Inspection | 1-3 weeks | Pass final inspection, receive certificate of occupancy |
California Fast-Track
Under California law, cities must process ADU permits within 60 days of a complete application. If they fail to act, the permit is deemed approved. This is a powerful protection for homeowners.
Required Documents
- Completed permit application form
- Site plan showing ADU location, setbacks, and existing structures
- Architectural floor plans and elevations
- Structural engineering calculations (if required)
- Title 24 energy compliance documentation
- Soils report (for some jurisdictions)
- Proof of property ownership
Inspection Stages
Foundation
Verify footings and foundation before concrete pour.
Framing
Structural framing, shear walls, and roof framing inspection.
Rough MEP
Mechanical, electrical, and plumbing rough-in inspection.
Insulation
Insulation and energy efficiency compliance check.
Drywall
Drywall installation and nailing inspection.
Final
Complete building inspection and certificate of occupancy.
Tips to Speed Up Permitting
- Schedule a pre-application meeting with your city planning department
- Use pre-approved plans if your city offers them — can cut review time by 50%
- Submit a complete application the first time — incomplete apps get sent back
- Hire an experienced ADU designer who knows your city's requirements
- Respond to plan check corrections promptly
- Know the 60-day rule (California) and advocate for yourself if review is slow
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