ADU Permit Process Step-by-Step

The permit process is where many ADU projects stall. Not because of bureaucratic malice, but because homeowners don't know what to expect, get surprised by the steps, and lose weeks or months waiting on things they could have anticipated.

Here's what the process actually looks like.

Before You Submit: Pre-Application Research

Before spending money on drawings, spend a few hours on free research.

Look up your city's ADU rules. Most cities have ADU handouts or fact sheets on their planning department websites. These tell you what's allowed on your lot before you hire anyone.

Check if your city has pre-approved plans. A growing number of California cities have libraries of pre-approved ADU designs. If you choose a pre-approved plan, your plan check is dramatically faster. Los Angeles, San Jose, and Sacramento all have these programs.

Request a pre-application meeting (also called a preliminary review). Many planning departments offer informal meetings where you can describe your project and get early feedback. This is free or low-cost, and it can catch problems before you've paid for drawings.

Step 1: Hire a Designer and Get Plans

You need stamped construction drawings to apply for a permit. Your options:

• ›Architect: Most expensive ($10,000–$25,000 for a full ADU), most flexibility, handles complex projects and sites well
• ›Draftsperson or designer: Less expensive ($3,000–$8,000), sufficient for most straightforward projects
• ›Prefab manufacturer: Companies like Abodu, Cover, or Mighty Buildings provide plans as part of their product package
• ›Pre-approved plan library: If your city has these, you select a design and customize the finishes

Good plans include site plans, floor plans, elevations, sections, foundation plans, framing plans, and all required notes and calculations. Incomplete plans are the most common reason for plan check rejection.

Step 2: Submit for Plan Check

You submit your plans to the city's building department along with a permit application and the initial plan check fee.

The building department assigns a plan checker who reviews the drawings against the California Building Code, local ordinances, and Title 24 (energy code) requirements. They also route your plans to other departments: planning, fire, public works, and sometimes utilities.

State law requires cities to approve or deny ADU permit applications within 60 days. Most cities are faster than this now, but some still stretch it out through the comments and correction process.

What happens if there are corrections? The plan checker sends a list of required changes. Your designer revises the plans and resubmits. This is called a "plan check correction cycle." A first cycle is normal. Three or more cycles signals a problem, usually with the original drawings.

Step 3: Permit Issuance and Fee Payment

Once plans are approved, the city issues the permit and collects all fees. This is where the final tally of permit costs becomes clear.

Fees typically include:

• ›Building permit fee (based on project valuation)
• ›Plan check fee
• ›Mechanical, electrical, and plumbing fees
• ›School fees (if your ADU is over 500 sq ft)
• ›Impact fees (if over 750 sq ft and your city charges them)

The permit is valid for a set period, usually 12–18 months, and requires periodic inspection activity to stay active.

Step 4: Construction and Inspections

Once the permit is in hand, work can begin. Construction inspections are required at specific milestones. The building inspector must sign off on each stage before work can proceed to the next.

Common inspection stages:

• ›Foundation: After forms are set, before concrete is poured
• ›Framing: After all walls, floors, and roof framing are complete
• ›Rough-in: After plumbing, electrical, and HVAC are roughed in but before walls are closed
• ›Insulation: After insulation is installed, before drywall
• ›Drywall nailing: In some jurisdictions, after drywall is hung but before it's taped
• ›Final: Everything complete, ready for occupancy

Failing an inspection delays the project. The most common reasons: framing not matching the approved plans, electrical or plumbing work not meeting code, or missing required blocking or hardware. Your contractor should know what's required at each stage and prepare accordingly.

Step 5: Certificate of Occupancy

After the final inspection passes, the city issues a Certificate of Occupancy. This document confirms the ADU is legally habitable and compliant with all codes.

Without a CO, you cannot legally rent the unit. Some homeowners skip this step and rent anyway. It's a mistake. If something goes wrong, insurance won't cover an unpermitted dwelling, and you can face significant fines and legal liability.

Realistic Timelines

Timeline varies significantly by city, project type, and backlog. Rough ranges:

Total range: 6 months (very smooth) to 18+ months (complex site, multiple correction cycles, busy city)

What Causes Delays

The most common culprits:

• ›Incomplete plans: Plan checkers reject drawings that are missing required details, triggering correction cycles
• ›City backlog: Some cities are simply slow. Check with your designer or other homeowners who have recently permitted projects in your city
• ›Scope changes during construction: Changing the design after permit approval requires an amended permit and re-review
• ›Failed inspections: Each failed inspection adds days or weeks depending on the inspector's availability

The best thing you can do to avoid delays is hire a designer with recent local permit experience. They know what the city expects, and well-prepared drawings clear plan check faster.