The County of Contra Costa Jose permits ADUs across most residential zones. The County of Contra Costa follows both state and local ADU laws, allowing most single-family homes to build one detached ADU and one Junior ADU (JADU) per lot. Multi-family properties may be eligible for multiple ADUs, depending on site conditions.

County of Contra Costa aligns with California’s broader ADU legislation but has its own requirements for height, setbacks, and design review.

• Detached ADU: an accessory dwelling unit detached from a primary dwelling unit
• Attached ADU: an accessory dwelling unit attached to a primary dwelling unit
• Conversion ADU: Converted from a garage, basement, or internal space
• Junior ADU (JADU): ADUs and JADUs allowed on residential lots. JADU must be within existing home with its own exterior access max 500 sq ft

• Maximum Size:
  
  • Detached: Up to 1000 sq ft
  • Attached: 850 square feet if the accessory dwelling unit provides one bedroom or 1000 square feet if the accessory dwelling unit provides more than one bedroom
• Setbacks:
  
  • Minimum 4 ft from side and rear property lines
• Height Limits:
  
  • Detached: up to 35 ft
  • Attached: maximum 25 ft
• Parking Requirements:
  
  • Additional parking is not required if the ADU is:
    
    • The accessory dwelling unit is located within one-half mile walking distance of public transit
    • The accessory dwelling unit is located within an architecturally and historically significant historic district
    • The accessory dwelling unit is an internal conversion

To build an ADU in County of Contra Costa, the following approvals are typically required:

• Zoning compliance review: Planning approval is required before applying for a building permit
• Site plan and elevations: Needed to show the layout, dimensions, and exterior views of the ADU
• Architectural drawings: Required to detail the construction, including structural calculations
• Title 24 energy documentation: A Title 24 energy report is mandatory and must be stamped/registered
• Permit submission through an online portal: Applications are submitted via the County’s ePermits Center for both planning and building permits
  

Homeowners should also review County of Contra Costa’s current fee schedule, utility connection requirements, and fire code compliance.

Permit review times vary but generally fall between 8 to 12 weeks depending on project complexity, completeness of plans, and county workload. Projects requiring plan check corrections or multiple resubmittals may take longer. Working with design or permit professionals familiar with County Of Contra Costa ’s ADU process can help streamline and speed up approvals.

Most residential zones in the County of Contra Costa allow ADUs, including single-family and multifamily districts. There are no minimum lot size requirements for most ADU types under state law. However, properties located in hillside, fire-risk, or environmentally sensitive overlay zones may be subject to additional development standards or review.

For the most current and complete information, refer directly to the County of Contra Costa.