Santa Clara County ADU Guidelines and Information

An Accessory Dwelling Unit, previously referred to as a secondary dwelling, is intended to provide a valuable and relatively affordable form of housing for family members, the elderly, students, in-home health care providers, individuals with disabilities, and others, within existing neighborhoods and on existing legal lots. ADUs may be attached or detached, newly built spaces or converted from an existing structure. An ADU must have its own living, sleeping, eating, cooking, and sanitation facilities, including a full kitchen and bathroom. A Junior Accessory Dwelling Unit, or Jr. ADU, must be contained entirely within a single-family residence or ADU. It must have a separate entrance and its own kitchen but may share a bathroom with the attached dwelling. 

If your lot is a legal lot of record that has an existing single family residence (or a single family residence is being constructed on it) in most rural, urban residential, or commercial zones, you may build up to one ADU and one Jr. ADU IF there are adequate water and sewage services, minimum setback requirements are maintained, AND fire and life safety standards are met. ADUs are subject to building code standards, including planning review and building permits, and may have additional requirements, such as parking.

 ADUs may be built up to 1200 square feet in some cases. Attached ADUs can never be more than 50% of the primary dwelling size except to allow for a minimum size of 800 square feet. ADUs may be up to 16 feet in height, although taller structures allowed if they meet residential setback requirements. A garage or carport of up to 400 square feet and a deck or porch of up to 400 square feet may be added and does not count towards the floor area.