The Ultimate Guide to ADU Permits in California (2026)

Building an Accessory Dwelling Unit (ADU) in California has never been more accessible, thanks to progressive state laws. However, navigating local permit costs, zoning restrictions, and the application process can still be complex. This comprehensive guide breaks down everything you need to know.

1. Do You Need a Permit for an ADU in California?

Yes. Regardless of the size or whether it's attached or detached, all ADUs require a building permit. California state law (SB 1337 and AB 68) has streamlined this process, prohibiting cities from imposing unreasonable delays or excessive fees, but the permit is still mandatory to ensure safety and zoning compliance.

2. Breakdown of ADU Permit Costs

Permit costs are not a flat fee; they are calculated based on the project's valuation and square footage. A typical fee schedule includes:

• Plan Check Fees: Usually 50-65% of the total permit fee, paid upfront to review your architectural drawings.
• Permit Issuance Fees: Based on the square footage (e.g., $1.50 to $3.00 per sq. ft.).
• School & Impact Fees: Waived for ADUs under 750 sq. ft. For larger units, fees may apply but are often significantly reduced compared to primary residences.

3. Key California ADU Laws You Must Know

State law overrides local ordinances in several key areas to encourage housing:

• Setbacks: Cities cannot require more than a 4-foot rear and side yard setback for an ADU.
• Parking: No additional parking is required if the ADU is located within 0.5 miles of public transit, or if it's created within an existing garage.
• Owner-Occupancy: The requirement for the homeowner to live in either the primary residence or the ADU has been suspended until at least 2025.

4. The Step-by-Step Application Process

1. Pre-Application Research: Use PermitEngine's city search to find exact fees for your specific city.
2. Hire a Professional: Engage an architect or designer familiar with local ADU ordinances to draft your plans.
3. Submit to the Building Department: Most cities now offer online portals (e.g., ePlan room) for faster submission.
4. Address Corrections: The city will return a "correction sheet." Your designer must update the plans accordingly.
5. Permit Issuance & Inspections: Pay the remaining fees, receive your permit, and schedule mandatory inspections (foundation, framing, electrical, final).