An accessory dwelling unit, or ADU, is a separate living area on a property with a proposed or existing primary residence. ADUs, sometimes called granny flats or backyard cottages, are cost-effective housing options because homeowners can create new living spaces without buying property. ADUs maximize space and expand housing options in existing neighborhoods.
An ADU must be independent from the main housing unit on the property and include a permanent kitchen and a minimum ¾ bathroom, including a toilet, sink, and shower. California has relaxed ADU laws and streamlined the permit approval process to encourage building ADUs and creating more affordable housing.
Source: Adobu