Accessory Dwelling Unit (ADU) Resources

On February 27, 2024, the Board of Supervisors approved an extension to the Accessory Dwelling Unit (ADU) Fee Waiver Program through December 31, 2024, which offers property owners County fee waivers for the development of ADUs and JADUs in unincorporated Marin County (Board Packet, Resolution 2024-12). The fee waiver includes deeper incentives for ADUs that are rented to low- or moderate-income households.

Fee Waiver Options

• Up to $1,500 for eligible JADUs (no income restriction)
• Up to $2,500 for eligible ADUs (no income restriction)
• Up to $5,000 for eligible ADUs restricted for a household earning a moderate-income (81-120% of the Area Median Income)
• Up to $10,000 for eligible ADUs restricted for a household earning a low-income (below 80% of the Area Median Income)

To qualify for the waiver, the applicant must affirm that the ADU/JADU will not be used as a short-term rental. To receive one of the higher tiered waivers intended for moderate- and low-income households, the applicant will need to place a deed-restriction on the property confirming the unit will be rented to a household at the income level specified. More details are available in the panels below.

Process and Application

The fee waiver is structured as a reimbursement. The applicant will first need to consult with the Planning Division to determine all the fees and permits needed for the project.

The general fee waivers ($1,500 and $2,500) are processed directly by Staff. You do not need to submit a separate application.

To apply for either the $5,000 or $10,000 waiver, complete this online application after consulting with the Planning Division and Building & Safety Division. Applications are accepted on a rolling basis.

The Area Median Income (AMI) is determined regionally, and households are considered “low-income” or “moderate-income” in relation to this figure. The AMI establishes income and rent limits for these categories by household and unit size. In accordance with the most recently available data, the thresholds include:

Low-Income Maximum Thresholds (up to 80% AMI)

Moderate-Income Maximum Thresholds (up to 120% AMI)

ADUs have been known by many names: granny flats, in-law units, backyard cottages, secondary units, and more. They provide additional independent living units within the footprint of existing residential properties. They can either be attached or detached to the primary structure on the lot. ADUs are required to have a full kitchen, separate bathroom, and separate entrance.

There are two ADU categories detailed in the Marin County Development Code (Section 22.32.120):

Category 1: Statewide Exemption

ADUs which meet the criteria below.

In single-family development:

• Contained entirely within the building area of an existing single-family residence
• Contained entirely within the building area of an existing outbuilding. The project may include an addition of up to 150 square feet of floor area to provide access to the unit (provided the access meets minimum rear and side setbacks of four feet).
• Does not exceed a floor area of 800 square feet and has a minimum rear and side yard setback of four feet.
• Up to two Category 1 ADUs are allowed if at least one of the units is located in an existing or proposed single-family dwelling or outbuilding, and one is located in a new construction outbuilding.

In multi-family development:

• Up to two detached ADUs, provided each unit does not exceed 800 square feet in floor area and has minimum side and rear yard setbacks of four feet.
• Multiple ADUs built within portions of the existing building area that are not conditioned to be habitable (such as boiler rooms, storage rooms, passageways, attics, basements, and garages).
• At least one ADU can be built within a multi-family dwelling building, with maximum of 25% of legal units for multi-family buildings with 5 or more units.

Category 2: Permit

ADUs which meet the criteria below and shall be subject to Accessory Dwelling Unit Permit approval.

• Attached ADU: Maximum floor area of unit contained entirely within an addition to an existing single-family residence or contained partially within a single-family residence and the addition, not to exceed 50% of the floor area of the existing residence or 1,200 square feet, whichever is more restrictive. A one-bedroom unit up to 850 square feet is allowed, and two-bedroom up to 1,100 square feet is allowed (notwithstanding any floor area restrictions).
• Detached ADU: Maximum floor area of 1,200 square feet, provided it does not exceed the allowable floor area. A one-bedroom unit up to 850 square feet is allowed, and two-bedroom up to 1,100 square feet is allowed (notwithstanding any floor area restrictions).

The specific criteria for your project will be determined during the permitting process.

A JADU is an additional, independent living unit with a separate entrance generally created through the conversion of an existing bedroom. A property owner can voluntary have an existing building area recognized as a JADU if it meets the following criteria:

• No larger than 500 square feet and must be contained entirely within a single-family dwelling structure
• Include a kitchenette (wet bar), but not a full kitchen
• Separate entrance with an interior entry to the main living area if the unit does not contain a separate bathroom
• Only one JADU on the property
• Property must be owner-occupied, unless the owner is a government agency, land trust or housing organization
• Recorded deed-restriction that prohibits the sale of the unit separate from the single-family, which must be provided to the agency

The specific criteria for your project will be determined during the permitting process.

For an overview of permits and fees for your ADU or JADU project, please begin by contacting the Planning Division.

Examples of some of the most common Community Development Agency ADU fees include:

• $515 ADU Planning Permit Fee. Required if the ADU is not exempt.
• $5,641 - $8,633 Coastal Planning Permit Fee. Required if the ADU is located in the Coastal Zone.
• $6,500 - $10,000+ Building & Safety Permit Fee. Dependent on square footage of ADU.
• $3,500 - $8,000 + Environmental Health Services Water & Septic Permit Fee. Required for a new system or if there will be modifications to an existing system.

The Department of Public Works may assess fees for your project, if applicable, such as a traffic mitigation fee. For more information, contact the Department of Public Works: (415) 473-6530. 

• ADU Marin
  • ADU Marin: ADU Glossary
  • ADU Marin: ADU Workbook, A Complete Guide To Planning An Accessory Dwelling Unit In Marin County
  • ADU Marin: Webinar Series "You Too Can Build an ADU"