City Council to Review (ADU) "Accessory Dwelling Unit" Ordinance


Accessory Dwelling Units (ADUs) are an important and well respected piece of Mill Valley’s smaller scale, affordable housing stock. The proposed modifications to ADU regulations (contained the Mill Valley Municipal Code Section 20.90) incorporate direction received from City Council and Planning Commission to establish Junior ADU regulations and create additional regulations, where possible, to ensure that ADUs are maintained as truly separate, rentable units and used for the intended purpose of a dwelling unit. 


On January 24, 2019, Mill Valley City Council will review the proposed modifications to the ADU Ordinance summarized below, and will consider adoption of the Ordinance. The Draft Ordinance: 1) clarifies state regulations governing the construction of ADUs; 2) defines the overall review and approval process; 3) proposes additional regulations for those ADU applications that do not qualify for ministerial approval under the state statute (government code section 65852.2); and 4) proposes to modify the square footage bonus received for constructing new ADUs (known as the “Floor Area Bonus”).


The Draft Ordinance is summarized below and can be downloaded prior to the meeting, as part of the staff report go to, January 24, 2019 City Council meeting.


Summary of Proposed Modifications

The Draft Ordinance incorporates direction received from Planning Commission and previous feedback received at City Council, including the following substantive changes:


Discretionary “Exceptions”.  The Draft Ordinance establishes a review and approval process for those applicants that wish to build an ADU on their property, but do not meet lot size or lot coverage requirements, or for those existing parcels that currently have more than one ADU on the property. This process is intended to help address the interests of owners with properties that do not meet standards, while also fostering additional infill housing in town. 


The Draft Ordinance indicates that an “exception” may be granted through the Design Review process, if the proposed exception to the development standards do not adversely affect the health or safety of persons residing or working in the neighborhood of the property of the applicant and will not be detrimental to the public welfare or injurious to property or improvements in the neighborhood. In order to qualify, the Single Family residence must have 2 off-street parking spaces for the primary residence and the applicant must satisfy the additional rental restriction requirements discussed below. 


Floor Area “Bonus” Square Footage. The bonus granted for creating an ADU is being modified as follows:


Lot Size

Max FAR/

House Size

PROPOSED Calculation

PROPOSED Square Footage Bonus


Square Footage Bonus

Under 8,000


May apply as an “exception”

(discussed above)

Based on lot size, up to 12%




Up to 12% of

FAR Formula

(MVMC 20.16.040)



























Over 15,000


Not Eligible



Lots over 15,000 will not be eligible for the bonus under the new proposed regulation, since typically larger scale lots do not need additional square footage to build. It was also acknowledged that larger lots are typically in the hillsides, and may not be the most appropriate area for additional square footage.


Additional Design Standards required for those ADUs created with the Floor Area Bonus.

  • No internal connections to primary residence allowed for those ADUs requesting an exception to standards;

  • A closet required for every bedroom space (defined in the draft ordinance);

  • The primary residence must comply with parking standards (2 off-street parking spaces and 1 guest space when on-street parking not available); and

  • At least 1 parking space required for the ADU. 


Additional Deed Restriction/Rental Restrictions for those ADUs created with Exceptions and/or Floor Area Bonus.

  • As part of the discretionary approval of the ADU, a deed restrictions shall be recorded, indicating that the ADU be rented to any of the following: an “Affordable Household” (Moderate, low or very low income affordability levels, as defined in the Draft Ordinance); an adult immediate family member (defined in the Draft Ordinance); or to a service provider or other member of the community.

  • Verification of use shall be submitted by the owner to the City on an annual basis as part of a business license. Documentation shall include rental agreement(s) documenting the rent charged, household size, and gross household income. 


Minimum Lot Size.

The proposed Ordinance has been modified to address state ADU regulations (Government Code 65852.2(e)), which allows ADUs to be built within an existing primary residence, garage, or structure regardless of lot size. However, a jurisdiction may still establish minimum lot sizes for new ADUs created by way of new square footage or the conversion of garages/accessory structures.


Junior ADUs. The Draft Ordinance incorporates state regulations establishing Junior ADUs in the City. Junior ADUs are different from Standard ADUs in that the Units: are not be separate from the main unit; may (or may not) share a bathroom; do not have a full kitchen (they are allowed an efficiency kitchen); and cannot be larger than 500 square feet.  State law also requires owner occupancy of any property with a Junior ADU.


Approval Process and Termination of Use. The Draft Ordinance clarifies the approval process for ministerial and discretionary ADU applications, and creates a process for terminating an ADU permit, which will help track and account for existing ADUs in the City.


For More Information:

City Council meetings are held at 6:30pm in Council Chambers located at Mill Valley City Hall, 26 Corte Madera Avenue, Mill Valley, CA 94941.  For more information or to provide comments on the Draft Ordinance, contact Danielle Staude at dstaude@cityofmillvalley.orgor (415) 388-4033.