California Building Code ADU Requirements: A User-Friendly Guide

Feb 1

California has streamlined the process for you to build Accessory Dwelling Units (ADUs), providing a more flexible and affordable housing option.

Understanding the California Building Code (CBC) requirements is essential to ensure compliance and a smooth approval process.

This guide breaks down key aspects of ADU construction, permitting, and safety requirements.

1. Types of ADUs

Each type of ADU has different structural and zoning implications, so choosing the right type depends on your available space and needs.

California recognizes three primary types of ADUs:

Detached ADUs – Standalone units separate from your main house.
Attached ADUs – Units attached to your primary residence.
Converted ADUs – Existing spaces (e.g., garages, basements) converted into living units.

2. Size and Setback Requirements

Size and setback regulations ensure that your ADU fits within the lot while maintaining adequate space between structures.

You can build ADUs up to 1,200 square feet, depending on lot size and local zoning.
Detached ADUs must have at least 4-foot side and rear setbacks.
Converted ADUs typically do not require additional setbacks if within an existing structure.

3. Height Restrictions

Height restrictions help preserve neighborhood aesthetics and prevent overshadowing adjacent properties.

The standard height limit is 16 feet, though some local ordinances allow up to 25 feet in certain cases.

4. Parking Requirements

These parking rules support transit-oriented development and reduce the burden on you in urban areas.

No parking is required if your ADU is within ½ mile of public transit.
One parking space is required for ADUs outside transit-accessible areas.
Replacement parking is not required if you convert a garage into an ADU.

5. Permitting Process

A streamlined permitting process reduces delays and makes ADU construction more feasible for you.

Your local jurisdiction must approve ADU permits within 60 days.
Ministerial approval ensures a faster process without a public hearing.
No discretionary approvals are required if your ADU meets state guidelines.

6. Fire and Safety Regulations

Fire and safety rules are crucial for protecting occupants and ensuring emergency accessibility.

Your ADU must comply with California Residential Code (CRC) fire safety regulations.
Fire sprinklers are not required if your primary residence does not have them.
Separate egress requirements (windows, doors) must be met for safe exits.

7. Utility Connections

Utility connection regulations help balance costs while maintaining proper infrastructure.

Your ADU may share water, sewer, and electricity with the main dwelling.
Separate utility connections may be required for detached ADUs but cannot be unreasonably costly.

8. Impact Fees

Waiving impact fees for smaller ADUs encourages their development as an affordable housing option.

If your ADU is under 750 square feet, you are exempt from impact fees.
Larger ADUs may require fees based on local jurisdiction regulations.

9. Rental and Owner-Occupancy Rules

These rules support stable housing availability and prevent excessive short-term rentals.

You can rent your ADU long-term, but most cities prohibit short-term rentals (under 30 days).
Owner-occupancy requirements were removed for new ADUs until 2030.

10. Junior Accessory Dwelling Units (JADUs)

JADUs offer a lower-cost housing solution that allows you to utilize your existing home space efficiently.

JADUs are smaller units (maximum 500 sq. ft.) within your single-family home.
They must share bathroom facilities with your main house or have a separate option.
Owner occupancy is required for JADUs.

Key Takeaways

California has made ADU construction more accessible, but local regulations still vary. Before building an ADU, check with your local planning department for specific zoning laws.

By following these state-mandated CBC requirements, you can add valuable living space while staying compliant with the law.

If you’re looking for expert guidance on designing and building your ADU, our team can help streamline the process and maximize your investment. Contact us today to learn more about how we can bring your vision to life.

For the full California ADU Handbook, visit the California Department of Housing and Community Development.

Andreaus R