A Homeowner’s Guide to ADU Permits in California

 Table of Contents
 1. What is an ADU?
2. Benefits of Building a Permitted ADU
 3. Understanding California ADU Permit Requirements
 4.  How to Overcome Zoning Hurdles for Your ADU
 5. FAQ
ADU

What is an ADU?

An Accessory Dwelling Unit (ADU) is a secondary housing unit on a single-family or multi-family residential lot. Commonly referred to as granny flats, in-law units, or backyard cottages, ADUs provide an affordable and efficient way to add livable space, generate rental income, or house extended family.

In California, ADUs have become a major component in tackling the state’s housing crisis. New statewide laws have streamlined the permitting process, encouraging homeowners to build legal ADUs on their property.

✅ Benefits of Building a Permitted ADU

  • Building a permitted ADU in California offers numerous benefits:
    • Increased Property Value: A legally permitted ADU adds substantial value and appeal to your property.

    • Rental Income: Generate consistent passive income by renting out your ADU.

    • Housing Flexibility: Accommodate aging parents, adult children, or guests comfortably.

    • Legal Protection: Permits ensure your ADU complies with local safety, zoning, and building codes.

    • Financing Opportunities: Legal ADUs are eligible for financing, refinancing, and potential tax deductions.

Understanding California ADU Permit Requirements

To build a permitted ADU, California homeowners must adhere to statewide guidelines and local zoning ordinances. Here’s what you need to know:


1. Eligibility & Zoning

  • Most single-family and multi-family lots are eligible for ADUs.

  • Zoning laws now allow at least one ADU and one Junior ADU (JADU) per lot.


2. Types of ADUs

  • Detached ADU – A stand-alone structure.

  • Attached ADU – Connected to the primary residence.

  • Garage Conversion – Converts existing garage space into a livable unit.

  • JADU – A smaller, integrated unit within the existing home, up to 500 sq. ft.


3. Size & Setbacks

  • Up to 1,200 sq. ft. for detached ADUs.

  • No minimum lot size requirement.

  • Setbacks: 4 feet from the rear and side property lines.


4. Permit Process Overview

  • Site Plan Preparation

  • Architectural and Engineering Plans

  • Submit Application to Local Building Department

  • Plan Review & Revisions

  • Building Permit Issuance

  • Construction & Inspections

🔧 Common ADU Permit Mistakes to Avoid

  • Skipping city consultation before starting design
  • Assuming your ADU doesn't need a permit

  • Not hiring licensed professionals

  • Ignoring local utility hookup rules

  • Underestimating timeline and costs

FAQ

Do I need a permit to build an ADU in California?

Yes. Even with relaxed laws, you must obtain a building permit from your local city or county planning department.

How long does it take to get an ADU permit?

The state mandates that local jurisdictions approve or deny applications within 60 days.

What’s the cost of permitting an ADU?

Permit fees vary by city, but you can expect to pay between $3,000–$8,000 depending on the size and location of the unit.

Can I rent out my ADU?

Yes. Permitted ADUs can be rented out, but some cities require owner-occupancy or prohibit short-term rentals (under 30 days).

What if I already built an unpermitted ADU?

You may be eligible for ADU amnesty programs that allow homeowners to bring non-permitted units into compliance.