If you’re considering adding an Accessory Dwelling Unit (ADU) to your property in Marin County, California, it’s essential to understand the local requirements to ensure a smooth and compliant building process. ADUs offer a fantastic opportunity to expand living space, generate rental income, or provide housing for family members. However, navigating the specific regulations in Marin County is crucial.

Types of ADUs in Marin County

Marin County recognizes several types of ADUs:

  • Attached ADUs: These units are connected to the main residence and can be located at the back, side, or front of the house.
  • Detached ADUs: Separate structures situated on the same property as the primary residence.
  • Junior Accessory Dwelling Units (JADUs): Smaller units, often created by converting an existing bedroom within the main house. JADUs must have a kitchenette and can share a bathroom with the primary residence. They are limited to a maximum size of 500 square feet.
    marincounty.gov

General Requirements

Understanding the general requirements for ADUs in Marin County is vital:

  • Zoning: Properties zoned for single-family, two-family, or multifamily use may be eligible to build ADUs.
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  • Size Limits:
    • Detached ADUs: Up to 1,200 square feet.
    • Attached ADUs: Cannot exceed 50% of the existing residence’s floor area.
    • JADUs: Maximum of 500 square feet.
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  • Height Restrictions: Detached and attached ADUs can reach a height of 16 feet. For anything higher, it’s advisable to consult with the county planning office.
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  • Setbacks: A minimum setback of 4 feet from side and rear lot lines is required for detached ADUs. Front setbacks should comply with the standards of the primary structure. No setback is required if converting a legal garage.
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  • Parking: One parking space is generally required for ADUs unless:
    • The ADU is located within one-half mile walking distance of public transit.
    • It’s part of the proposed or existing primary residence or an accessory structure.
    • On-street parking permits are required but not offered to the occupant of the ADU.
    • There is a car share vehicle located within one block of the ADU.
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  • Owner Occupancy: Currently, there is no owner occupancy requirement for ADUs in Marin County. However, JADUs do require the property owner to reside on the property.
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Permitting Process

The permitting process for ADUs in Marin County is designed to be straightforward:

  • Ministerial Approval: Many ADUs can be approved ministerially, meaning they don’t require discretionary review. This streamlines the process, allowing for quicker approvals.
    marincounty.org
  • Building Permits: Regardless of the type of ADU, obtaining the necessary building permits is essential to ensure compliance with local building codes and safety standards.

Benefits of Building an ADU

Constructing an ADU in Marin County offers several advantages:

  • Rental Income: Renting out an ADU can provide a steady source of income.
  • Housing for Family Members: ADUs are ideal for housing elderly parents, adult children, or caregivers, allowing for proximity while maintaining privacy.
  • Increased Property Value: Adding an ADU can enhance the overall value of your property by providing additional living space.