What Are the Requirements for ADU Permits in California?

Building an Accessory Dwelling Unit (ADU) in California is an excellent way to add extra living space, generate rental income, or provide housing for family members. However, navigating the permit process can feel overwhelming due to various zoning laws, building codes, and regulations. Understanding the ADU permit requirements from the start helps ensure a smooth approval process, avoiding costly delays or compliance issues.

California has made significant legal changes in recent years to encourage ADU development, including Senate Bill 9 (SB 9) and Senate Bill 13 (SB 13). These laws have streamlined the permitting process and removed many barriers to construction. Below is a step-by-step breakdown of what homeowners need to know when applying for an ADU permit in California.

1. Zoning and Property Eligibility

Before submitting an application, checking local zoning laws is essential. California allows ADUs statewide, but cities and counties may have specific zoning requirements.

Key Zoning Requirements:

• Allowed in Residential Zones – ADUs can be built on properties zoned for single-family or multifamily use.

• Lot Size Restrictions – Unlike the past, most jurisdictions no longer require a minimum lot size.

• Number of ADUs Allowed – Single-family lots can have one detached ADU and one Junior ADU (JADU). Multifamily properties may allow multiple ADUs, depending on existing structures.

• Setback Rules – Typically, ADUs must be at least 4 feet from side and rear property lines.

Cities may have additional design and placement regulations, so checking with the local planning department is recommended.

2. ADU Size and Height Restrictions

California law establishes maximum and minimum size limits for ADUs. However, local governments may impose their own restrictions.

ADU Size Requirements:

• Detached ADUs – Up to 1,200 square feet, regardless of the lot size.

• Attached ADUs – Cannot exceed 50% of the primary residence’s square footage but can be up to 1,200 square feet.

• Junior ADUs (JADUs) – Limited to 500 square feet and must be part of the existing home.

• Height Limits – Typically 16 feet, but some areas allow up to 25 feet depending on zoning.

Smaller ADUs, such as studio units, may have relaxed building requirements compared to larger, full-sized ADUs.

3. Parking Requirements

One of the biggest concerns for homeowners is whether additional parking spaces are required. California law has significantly reduced ADU parking requirements.

Parking Rules:

• No additional parking is required if the ADU is located within half a mile of public transit.

• No parking is required if the ADU is part of an existing structure conversion.

• If parking is required, one space per unit or bedroom is standard.

• Parking can be in setback areas, driveways, or tandem configurations.

4. Permit Application Process

Submitting an ADU permit application to the local planning department is the first formal step. Many cities offer an online application process.

Required Documents:

• Completed application forms from the local building department.

• Site plans showing the location of the ADU on the property.

• Architectural drawings, including floor plans, elevations, and structural details.

• Title 24 energy compliance report, required under California’s energy efficiency laws.

• Utility plans, if new plumbing, electrical, or HVAC systems are needed.

Permit fees vary by city but typically range between $1,000 and $10,000 depending on the project size.

5. Utility Connections and Impact Fees

ADUs must have proper utility connections, but California has made the process more affordable for homeowners.

Key Utility Considerations:

• Detached ADUs may require separate utility connections.

• Attached ADUs and JADUs can typically share utilities with the primary residence.

• Fire sprinkler systems may be required for some ADUs, depending on local building codes.

• Impact fees are waived for ADUs smaller than 750 square feet but may apply to larger units.

Consulting with local utility providers helps determine the best approach for water, sewer, and electrical connections.

6. Fire and Safety Regulations

California requires ADUs to meet strict fire and safety standards to ensure occupant protection.

Fire Code Requirements:

• Smoke alarms and carbon monoxide detectors must be installed in all ADUs.

• Fire-resistant materials may be required for structures close to property lines.

• Detached ADUs may require fire sprinklers if the primary home has them.

Proper ventilation, insulation, and emergency escape routes must be incorporated into the design.

7. Construction and Final Inspection

Once the permit is approved, construction can begin. Homeowners must follow California Building Code (CBC) standards to ensure compliance.

Key Construction Steps:

• Site Preparation – Clearing and leveling the land, if necessary.

• Framing and Utilities Installation – Electrical, plumbing, and HVAC systems.

• Interior Finishing – Drywall, flooring, cabinetry, and fixtures.

• Final Inspection – City officials inspect the unit before issuing a Certificate of Occupancy.

Passing the final inspection is required before legally using or renting the ADU.

Conclusion

Navigating ADU permit requirements in California can be complex, but understanding zoning laws, size limits, parking rules, and utility needs simplifies the process. Working with experienced professionals ensures a smooth approval and construction experience. If there are any questions about ADU permitting or requirements, feel free to leave a comment, and an expert will respond as soon as possible.