Occasionally referred to as “granny flats",  "in-law units", "studio apartments” and “secondary dwellings”. ADU’s can be created by converting a existing garage at ground level, building above the garage, converting an existing attic, finishing an existing basement or built as a separate structure. ADU’s can range in square footage depending on the city or county in which the proposed ADU is being considered. You must confirm with your local building officials (building department, permit center) to determine if an ADU is allowed on a perspective property and what the criteria is for the ADU. Land use division may need to be your first contact.
The ADU shown in the adjacent photo is a 1-bedroom, 600 sq.ft. Barrier Free structure with loft storage above the bedroom and bathroom.