Mendez & Son's Construction Inc
CALIFORNIA ADU PERMIT PROCESS: WHAT TO EXPECT START TO FINISH
The permit process is the part of ADU construction that surprises homeowners the most. Not because it’s difficult to understand — we handle all of it — but because of how long it takes. Permitting is the longest single phase of most ADU projects. It runs on the city’s schedule, not yours.
California state law has done a lot to streamline ADU permitting statewide. But the process still takes time, still requires a complete and correct submittal, and still has enough variables that understanding it before you start makes the experience significantly less frustrating.
WHAT CALIFORNIA STATE LAW CHANGED
Before 2017, ADU permitting in California was largely left to local discretion. Cities could — and often did — impose restrictive zoning requirements, large setbacks, owner-occupancy requirements, and high fees that made ADU construction impractical or financially unviable.
A series of state laws passed between 2017 and 2023 fundamentally changed that. California essentially overrode local restrictions on ADUs and established a statewide framework that cities are required to follow.
These changes are real and they matter. But they don’t make ADU permitting instantaneous. They create a framework within which every city still runs its own process.
ADU Permitting Details
- ✓Ministerial approval — qualifying ADUs must be approved without discretionary review or neighbor notification
- ✓Reduced setbacks — no more than 4 feet for detached ADUs up to 800 sq ft
- ✓Fee limitations — no impact fees on ADUs under 750 sq ft; proportional fees above that
- ✓60-day review window — cities must act on complete applications within 60 days or the application is deemed approved
- ✓Parking elimination — ADUs cannot be required to provide additional off-street parking in most circumstances
WHAT THE PERMIT PROCESS COVERS
An ADU permit is actually multiple approvals running through different departments and sometimes different agencies. All of this has to be submitted together — or in the right sequence — for the review clock to start.
An incomplete submittal doesn’t begin the 60-day review window. It gets rejected administratively. That’s why we don’t submit until the package is genuinely ready.
We assemble and submit the complete package. You don’t interface with the building department.
THE PERMIT STAGES
Regardless of city, the ADU permit process follows the same general structure. Here are the four key stages from application to approval.
Design & Document Preparation
Permit-ready architectural drawings, structural engineering, and Title 24 calculations. Takes 4–8 weeks depending on project complexity.
Your involvement matters most here — layout and scope decisions must be locked downApplication Submission
Complete package — drawings, engineering, energy calcs, forms, and fees — gets submitted. The city assigns a plan checker and the 60-day clock starts.
Incomplete submittals get rejected before review beginsPlan Check & Corrections
The city routes your application to building, planning, fire, and public works. Each reviews independently. Most projects receive corrections on the first round.
We respond to corrections in 1–2 weeks to keep momentumPermit Issuance
Once all departments have signed off, the permit is issued and fees are reconciled. This is the green light for construction to begin.
Second-round reviews are faster — reviewers check corrections, not full plansAfter Permit Issuance: Inspections & Occupancy
The city doesn’t just review plans — they inspect the actual construction at specified milestones. Required inspections typically include foundation, framing, rough electrical, rough plumbing, insulation, and a final walkthrough.
Each inspection needs to be scheduled in advance and passed before work proceeds to the next phase. The final inspection and certificate of occupancy make the unit legal to occupy. Without it, the unit cannot be legally rented or occupied. That’s the finish line.
WHY TIMELINES STILL VARY BY CITY
California law standardized the rules. It didn’t standardize capacity. The 60-day review window is a legal requirement — it doesn’t mean every city is hitting it consistently or that the process feels fast when you’re in it.
Volume. Cities in high-demand areas like Palo Alto and Mountain View are processing significantly more ADU applications than they were five years ago. More applications through the same pipeline means longer queues.
Staffing. Building departments that have invested in ADU-specific staff or online review platforms process applications more efficiently than those that haven’t.
Correction culture. Some departments issue specific, actionable correction notices. Others issue broader comments that require more back-and-forth to resolve.
Utility coordination. Building permits and utility approvals run on separate tracks. In cities like San Mateo and Walnut Creek, the utility review can sometimes be the longer process.
Planning assumption: expect the full permit process to take 3 to 6 months in efficient jurisdictions and 5 to 9 months in more complex ones.
What Incomplete Submittals Cost You
- A rejected submittal restarts the queue — adding 4 to 8 weeks before review begins again
- Missing structural engineering when required
- Incomplete Title 24 energy calculations
- Site plan without utility locations, setback dimensions, or lot coverage calcs
- Missing egress windows, fire separation, or accessibility details
An extra week of preparation on the front end is worth far more than a rejected submittal that adds two months to the back end.
PARALLEL PROCESSING DURING PERMIT REVIEW
Waiting on permits doesn’t mean standing still. The time between submittal and permit issuance is when we move forward on everything that doesn’t require a permit:
Material procurement. Custom cabinets, windows, exterior doors, and specialty fixtures all have lead times. Ordering them during plan check means they arrive around the time construction starts.
Subcontractor scheduling. Trades are scheduled in advance — not lined up the week permits issue. A permit that issues without a construction team ready to start wastes weeks.
Site preparation. Clearing vegetation, staging access, and minor grading can proceed while plans are in review.
Utility pre-applications. Water, sewer, and electrical connection pre-applications can be submitted before the building permit is issued, preventing bottlenecks later.
When permits issue, we’re ready to start immediately. That preparation is how a project that takes 12 months in total doesn’t feel like it’s stalling for 6 of them.
What We Handle So You Don’t Have To
Permit coordination is part of our design-build process — not an add-on service. We manage the full permit process from application through certificate of occupancy.
- ✓Producing permit-ready architectural drawings and coordinating structural engineering
- ✓Submitting the complete application package
- ✓Tracking plan check status and following up with the department
- ✓Responding to correction notices quickly and completely
- ✓Coordinating utility connection approvals in parallel with building plan check
- ✓Scheduling and tracking all construction inspections
- ✓Managing the certificate of occupancy process at project completion
“If you want to be in your ADU by a specific date, start planning at least 12 to 15 months before that date. In complex jurisdictions, 18 months is more realistic.”
— Mendez & Son’s Construction
START YOUR
PERMIT PROCESS
The permit process starts with a complete, correct application. That application starts with a site assessment and design phase that produces the drawings the city needs to review. The earlier you start, the more control you have over when you finish.
Complete submittals · Faster approvals · No surprises
Serving Palo Alto · Mountain View · San Mateo
Walnut Creek · Redwood City · Bay Area