Santa Clara County has published a guide for ADU design and construction, Accessory Dwelling Units
New detached ADUs are permitted at this time while state law governs without regard to minimum lot sizes in either urban or rural zoning districts. The maximum allowed floorspace of a detached ADU is t,zoo se. ft., as determined by the County’s existing floor area definition.
In rural zones where existing height and storylimits permit them, ADUs constructed above another detached accessory use, such as a barn, garage, or storage building, maybe built with minimum five foot side and rear setbacks. However, the County encourages greater setbacks where possible to adhere to the intent and purpose of the ZoningOrdinance to reduce privac¡ shading, and noise impacts upon neighboring properties, and to maintain rural community character. Maintaining a 30 foot setbackin such situations is desirable.
Standard setbacks, story, floor area ratio (-nr and -nz), and height limits of each base and/or combining district applicable to all residences andbuildings still applyto new proposed detached ADUs. These are defined separately in the base district or combining zone regulations and are not affected by new state ADU laws.
Property Records can be found here.
The City Department of Planning and Development is a good place to start.