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Local ADU Rules

Mill Valley

Last Updated May 21, 2025

ADU Contact:

Danielle Staude, dstaude@cityofmillvalley.org

Standards	Details
Zones allowed	All residential and mixed-use zones with limited exceptions.
Lot Restrictions	None.
Minimum Lot Size
Min/Max ADU Size	Minimum: 150 square feet. Maximum: 1000 square feet for new construction. 1200 square feet for interior conversion of existing structure. JADUs Maximum: 500 square feet. One ADU and one JADU allowed on each single-family property. See state law for allowance for multifamily properties.
ADU Building Height	Generally, up to 16 feet (measured from natural grade). Above a garage: up to 25 feet.
Setbacks	None for conversions of existing living area or structure. 4-foot side and rear setbacks for new construction, qualifying under state law. ADUs taller than 16 feet must meet the City’s setback standards. Side and rear setbacks must meet fire safety requirements.
Parking Requirements	One parking space per ADU unless 1) within ½ mile of transit, historic district or car share, or 2) created by converting or demolishing garage or carport, then none required. Tandem parking and parking in setbacks are both allowed.
Owner Occupancy	Not required for ADU or primary residence. Required for JADU.
Sample fees from recent permits	Conversion of Attached Garage $89,000 Valuation; $3,434 Fees Modular Detached ADU (324 SF) $72,000 Valuation; $4,202 Fees New Custom Detached ADU (500 sf with 300 sf loft) $265,000 Valuation; $8,200 Fees *Fees are specific to each project and will vary. Fees change regularly. These are provided as examples only.
Other requirements	A deed restriction must include that ADU or JADU 1) shall not be sold separate from primary dwelling unit, 2) shall be restricted to Gross Floor Area granted at time of building permit and cannot be converted back to the main living unit unless granted by the Planning Department, and 3) requirements must be maintained by future owners. Fire Sprinklers: Needed if required for primary residence.
Process	Complete applications reviewed by City within 60 days per State law. ADUs not defined in State Code, such as ADUs above a garage require Design Review Approval. Disclaimer: standards and process may vary. Consultation with the contact is recommended before starting any project.
Exceptions

Wondering what you can build?

Make sure you check out our Learning the Rules page for more step-by-step details