Accessory Dwelling Unit Permit
Accessory Dwelling Units are a permitted use in the RS and Planned Residential Districts. Accessory Dwelling Units may also be permitted in the RM and DR Districts on lots that contain a single family residence. For further information please see Chapter 20.90 of the Mill Valley Municipal Code.
The property owner must verify, under penalty of perjury at the time of application for the Accessory Dwelling Unit, that one of the two units on the property is or will be their primary residence.
No new second units are permitted on lots under 5,000 sq. ft.
The floor area of a second unit is limited to 30% of the maximum adjusted floor area permitted for the site, and the total floor area for the site, including the area of the second unit, must be within the maximum adjusted floor area permitted for the site.
The floor area of a second unit must be at least 150 square feet but no more than 1,000 square feet.
If the unit is· a detached structure consisting of a garage and second unit, the total floor area of the garage/unit structure shall be .1,500 sq. ft. or less.
As an incentive to encourage small second units that can foster diverse and affordable housing options in the City, the following square footage is exempt (or can be deducted) from the FAR.
For lots between 5,001 and 8,000 square feet – no floor area exemption is permitted.
For lots of 8,001 to 10,000 square feet – the first 300 square feet of second unit floor area, or up to 800 square feet of a combined garage/ second unit, can be exempt from the adjusted floor area calculations.
For lots more than 10,000 square feet – the first 500 square feet of second unit floor area, or up to 1,000 square feet of a combined garage/ second unit, can be exempt from the adjusted floor area calculations.
Design Review is required for all Accessory Dwelling Units that utilize the Floor Area Exemption.
The above mentioned exemptions only apply to the construction of new Accessory Dwelling Unit, not the conversion of an existing garage or accessory building.