California ADU Rules: What Homeowners Need to Know (2026)

California has been at the forefront of accessory dwelling unit (ADU) legislation for years, and 2026 continues that trend. The state has passed multiple laws designed to make it easier and more affordable for homeowners to build ADUs on their property. Whether you are thinking about a garage conversion, a backyard cottage, or an attached addition, understanding the current rules is the first step.

What California Law Allows

Under state law, most single-family homeowners in California can build at least one ADU and one Junior ADU (JADU) on their property. Cities cannot impose minimum lot size requirements for ADUs, and they cannot require owner-occupancy as a condition of approval for ADUs permitted under state law. The state also caps impact fees for ADUs under 750 square feet and limits the time cities have to review ADU applications to 60 days.

Size Limits and Setbacks

Detached ADUs in California can be up to 1,200 square feet for a two-bedroom unit. One-bedroom and studio ADUs are capped at 1,000 and 850 square feet respectively. The maximum height for a detached ADU is generally 16 feet, though some cities allow up to 18 feet if the property is near public transit. Rear and side yard setbacks are limited to 4 feet. Cities like Los Angeles, San Jose, and Sacramento have implemented these state standards, though some local variations exist in how they interpret specific provisions.

Permitting and Costs

The permitting process for ADUs in California has been streamlined significantly. Most cities now have a dedicated ADU permit track with pre-approved plans available. In Los Angeles, the Standard Plan Program offers pre-reviewed ADU designs that can reduce approval times. The cost of building an ADU in California ranges widely, from around $100,000 for a basic garage conversion to $300,000 or more for a new detached unit, depending on size, location, and finishes. San Diego and the Bay Area tend to be at the higher end of that range.

Common Pitfalls

Despite the state's ADU-friendly laws, homeowners still encounter obstacles. HOA restrictions remain a gray area, with some associations attempting to block ADUs despite state preemption. Utility connection fees can add $10,000 or more to project costs in certain cities. Parking requirements have been largely eliminated by state law for ADUs near transit, but some cities still require one parking space for ADUs in other locations. Getting a clear picture of all costs and requirements before starting construction is essential.

Rental and Income Potential

Many California homeowners build ADUs to generate rental income. In high-cost markets like San Francisco, Oakland, and Long Beach, ADUs can rent for $1,500 to $3,000 or more per month. The state prohibits cities from restricting ADU rentals to below 30-day terms, meaning you can rent your ADU on a standard lease. Short-term rental rules for ADUs vary by city, so check local regulations if you plan to list on platforms like Airbnb.