An accessory dwelling unit, or ADU, is a unit with a full kitchen and bathroom that is accessory to residential. Also called a granny flat or second unit, it can be on a property with a home or apartment building. It can also be detached or attached. ADUs usually cost less than building a new home and homeowners can offer them as rental housing. They also provide living space for family members or caregivers on the same property. A junior ADU, or JADU, is like an ADU but its maximum size is 500 square feet. The JADU also has to be within the main home and have its own exterior access.