Accessory Dwellings Units

Santa Clara County provides for secondary dwellings (or Accessory Dwelling Units, or ADUs) in zoning districts that allow residential uses. There are provisions specific to rural zoning districts and urban unincorporated districts, and they vary based on lot size. 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. Additionally, a Junior ADU (Jr. ADU) is no more than 500 square feet and must be contained entirely within a single-family residence. It must have a separate entrance and an efficiency kitchen but may share a bathroom with primary dwelling.

New Accessory Dwelling Laws. 

California enacted laws in regards to Accessory Dwellings that went into effect January 1, 2020. The County updated its Ordinances to reflect these new laws. The new ordinance was adopted March 10, 2020. 

For general inquiries on Accessory Dwelling Units, please contact the Planning Division at (408) 299-5700 and ask to speak to a Planner on Duty.


Frequently Asked Questions regar​ding the changes to the State ADU laws:

  • Can I build an ADU on my​ property?

    • 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 a residential or mixed-use zone, California State Law allows you to 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.
  • How many ADUs can ​I build?

    • You may build up to one ADU and one Jr. ADU if your property qualifies. An ADU may be attached or detached from the primary residence. A Jr. ADU must be attached.
  • What if my lot is deed restricted​ or my HOA bars ADUs?

    • Under California State Law, deed restrictions and HOA rules that ban ADUs are void. But restrictions that do not unreasonably increase the construction cost or effectively prohibit construction of an ADU or Jr. ADU are allowed.
  • Must I live on the p​roperty?

    • California State Law does not require you to reside on the property between January 1, 2020 and at least January 1, 2025 in order to construct an ADU. But for Jr. ADUs, state law allows jurisdictions to require owner-occupancy of either the main residence or the Jr. ADU.
  • What if I have an existing ADU that is in violation of the building codes?

    • An owner may request a 5-year delay in enforcement of the building codes, which will be granted unless the violation impacts health and safety requirements.

More Informa​tion

  • ​Housing and Community Development ​Handbook for ADUs​
  • Baird+Driscoll Community Planning with the Chan Zuckerberg Initiative, a non-government entity, has developed an ADU cost estimate Calculator for County residents to get an approximate estimate of costs and return on building an ADU. This can be accessed here:

    DISCLAIMER: the calculator provides a rough estimate on costs and financing but does not include fire and school impact fees as they are paid separately to those agencies. The county bases their building permit fees as a percentage of the cost of construction provided by the applicant.


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