Accessory Dwelling Units (ADUs) have gone by many names, including granny flats, in-law units, and secondary units. By definition, an ADU is a self-contained, additional housing unit, on a permanent foundation, that contains a kitchen, bathroom, and a place to sleep. ADUs range in size from 150 square feet for a studio to 1,200 square feet for a unit with multiple bedrooms (see matrix for additional information).