The County of Marin permits ADUs across most residential zones. County of Marin 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 Marin aligns with California’s broader ADU legislation but has its own requirements for height, setbacks, and design review.

• Detached ADU: a separate building located on the same property as the main house
• Attached ADU: are attached directly to the main house
• Conversion ADU: Converted from a garage, basement, or internal space
• Junior ADU (JADU): JADUs are smaller versions of ADUs. They are often created by converting an existing bedroom

• Maximum Size:
  
  • Detached: Up to 1,200 sq ft
  • Attached: Up to 50% of the primary dwelling’s floor area
• Setbacks:
  
  • Minimum 4 ft from side and rear property lines for a new ADU ≤ 800 sq ft at 16 ft height
• Height Limits:
  
  • Detached: up to 16 ft
  • Attached: ADU should comply with height standards of the primary structure 
• Parking Requirements:
  
  • Additional parking is not required if the ADU is:
    
    • Located within ½ mile of public transit
    • Converted from an existing structure
    • In a historic or architecturally significant district

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

• Zoning compliance review: ADUs are permitted in all residential zones
• Site plan and elevations: Required for the permit application to show existing and proposed structures, layout, and exterior views
• Architectural drawings: Must include construction details, engineering calculations (e.g., foundation, framing), and any required civil or soils reports
• Title 24 energy documentation: Energy analysis (Title 24) along with CalGreen checklist must be submitted
  

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

Permit review times vary but are typically between 1 to 6 months depending on project complexity and city workload. Projects requiring corrections may take longer. Engaging professionals familiar with County of Marin’s ADU process can help streamline approval.

Most residential zones are eligible for ADUs, including R-1, R-2, and R-M zones. There are no minimum lot sizes for ADUs in most areas of the County of Marin. Some hillside or environmentally sensitive zones may have special restrictions.

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

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