California ADU Laws: What Bay Area Homeowners Need to Know

ADU Rules Have Changed Dramatically. Here Is Where Things Stand.

California has passed a series of laws over the past several years that make it significantly easier and cheaper to build an accessory dwelling unit on your property. If you looked into ADUs five years ago and decided it was too complicated, it is time to look again.

The state has removed many of the barriers that cities previously used to make ADU construction difficult. The goal is simple: California needs more housing, and ADUs are one of the fastest ways to create it.

Key California ADU Laws

AB 68 (2020) and SB 13 (2020) were the big game-changers. Together, they established statewide ADU standards that cities cannot override. Cities can still have their own ADU ordinances, but those ordinances cannot be more restrictive than state law on key points.

Among the most significant changes: cities must approve or deny ADU applications within 60 days. Impact fees for ADUs under 750 square feet were eliminated. Parking requirements for ADUs were removed in many situations. Owner-occupancy requirements were suspended (though some have since been reinstated in modified form). Setback requirements were reduced to 4 feet for rear and side yards for detached ADUs.

Size Limits

Under current California law, a detached ADU can be up to 1,200 square feet regardless of the size of your primary home. Attached ADUs can be up to 50 percent of the existing home's floor area, with a maximum of 1,200 square feet. Junior ADUs (JADUs) are limited to 500 square feet and must be created within the existing footprint of your home.

Setback Requirements

Detached ADUs have a 4-foot rear and side yard setback requirement under state law. Front yard setbacks follow local rules. If you are converting existing space (like a garage), no additional setbacks are required. Height limits vary by city but typically range from 16 to 25 feet for detached ADUs.

Bay Area Permit Process

The ADU permit process varies by city across the Bay Area, but the general steps are: design your ADU and prepare construction drawings, submit a permit application to your local building department, the city reviews your plans (they have 60 days to approve or deny), make any required corrections, receive your approved permit, begin construction, pass required inspections during construction, and receive your certificate of occupancy.

In practice, the process from application to approved permit takes 2 to 4 months in most Bay Area cities. Some cities are faster, some are slower. We have submitted ADU permits across the Bay Area and know what to expect from each jurisdiction.

Typical Bay Area ADU Costs

ADU construction costs in the Bay Area typically range from $150,000 to $350,000+ depending on size, finishes, site conditions, and whether the unit is detached or attached. A basic 400 square foot studio ADU on a flat lot might come in around $150,000 to $200,000. A fully finished 1,000 square foot detached ADU with a full kitchen and high-quality finishes will be closer to $300,000 to $350,000 or more.

These costs include construction but may not include design, engineering, permits, and utility connections. Factor those in when budgeting.

Is Your Property Eligible?

Most single-family residential properties in the Bay Area are eligible for at least one ADU. The best way to find out is to check your property's zoning, lot size, and existing structures against your city's ADU ordinance. Or, give us a call and we will do a quick feasibility assessment for free.