ADU Permit Process in California: Step-by-Step Guide for 2026

Jaime Costilla · 2026-03-20

The ADU Permit Process: What to Expect

Getting permits is the step most homeowners dread. It's confusing, bureaucratic, and every city handles it differently. Vision ADU can walk you through what to expect.

Here's the step-by-step process.

Step 1: Pre-Application Research (Week 1)

Before drafting any plans, you need to know what your city allows. This includes:

• Zoning verification: Confirm your property is zoned for an ADU (almost all single-family residential zones in California now allow ADUs)
• Setback requirements: California mandates 4-foot minimums for detached ADUs
• Size limits: Maximum 1,200 sq ft for detached, 50% of existing home for attached
• Lot coverage: Some cities limit total lot coverage percentage
• Parking: California has eliminated parking requirements for most ADU projects
• Utility capacity: Sewer, water, and electrical availability

For San Diego-specific guidance, read our San Diego ADU permit process guide.

Step 2: Design and Architecture (Weeks 2-6)

Once you know the rules, an architect creates construction drawings that include:

• Site plan: Shows the ADU location on your property with setbacks
• Floor plan: Interior layout with dimensions
• Elevations: Exterior views from all sides
• Structural details: Foundation, framing, and connection details
• MEP plans: Mechanical, electrical, and plumbing layouts

Your plans must also include Title 24 energy calculations -- California's energy efficiency requirements that specify insulation, windows, HVAC, and lighting standards.

Choosing the right floor plan for your goals at this stage saves money and time later.

Step 3: Structural Engineering (Weeks 3-5)

A licensed structural engineer must provide:

• Foundation calculations
• Framing specifications
• Lateral force resistance design (earthquake requirements)
• Connection details

This step typically runs parallel with architectural design. Read about the structural engineering phase in our construction series.

Step 4: City Submittal (Week 6-7)

You submit your complete plan set to your city's building department. The submittal package typically includes:

• Architectural plans (3-5 copies, depending on city)
• Structural calculations
• Title 24 energy compliance reports
• Soils report (if required by your city)
• Application forms
• Permit fees

Learn about the city submittal process in detail.

Step 5: Plan Check (Weeks 7-14)

This is where the city reviews your plans for code compliance. Plan check timelines vary dramatically:

California law requires cities to approve or deny ADU applications within 60 days. In practice, most cities meet this timeline, but complex projects or cities with staffing shortages may take longer.

Step 6: Plan Check Corrections (Weeks 12-16)

Almost every project gets "corrections" -- items the plan checker wants changed or clarified. Common corrections include:

• Fire-rated wall assembly details
• Electrical panel location or sizing
• Plumbing venting details
• Window egress requirements
• Energy compliance clarifications
• Structural connection details

An experienced ADU builder anticipates these corrections and minimizes them. This is one reason choosing the right builder matters so much.

Step 7: Permit Issuance (Week 14-16)

Once corrections are resolved, the city issues your building permit. You'll pay:

• Building permit fees
• Plan check fees
• School fees (if applicable -- ADUs under 750 sq ft are exempt)
• Utility connection fees

Step 8: Construction and Inspections

With permit in hand, construction begins. The city conducts inspections at key milestones:

1. Foundation/slab inspection
2. Underground plumbing
3. Framing inspection
4. Rough electrical
5. Rough plumbing
6. Rough mechanical (HVAC)
7. Insulation inspection
8. Drywall inspection
9. Final inspection

Learn about each phase in our 17-part ADU construction series.

Step 9: Final Inspection and Certificate of Occupancy

The city conducts a final inspection to verify everything matches the approved plans. Once passed, you receive a Certificate of Occupancy (or equivalent) and your ADU is officially legal to occupy.

How to Speed Up the Process

1. Use pre-approved plans: Cities like San Diego and Chula Vista offer pre-approved ADU plans that skip most of plan check
2. Submit complete packages: Missing documents cause delays
3. Hire an experienced ADU builder: We know what each city looks for and submit correction-proof plans
4. Respond to corrections quickly: Don't let corrections sit
5. Consider expedited plan check: Some cities offer faster review for an additional fee

Total Timeline: What's Realistic?

For a typical ADU project:

• Design and engineering: 4-8 weeks
• Permitting: 8-16 weeks
• Construction: 12-24 weeks (depending on project type)
• Total: 6-12 months

Read our complete guide on how long it takes to build an ADU for more detail.

Don't navigate permits alone. Book a free consultation with Vision ADU — we handle the permit process from start to finish.

Permitting is where most ADU projects stall. With Vision ADU, it doesn't have to. Contact us today and let our team handle the paperwork while you plan your new rental income.