Accessory Dwelling Units (ADUs) come in many forms. They range from small, freestanding buildings to additions on already existing homes. Known for adding functionality, ADUs are commonly designed for purposes such as in-law living, aging in place, rentals, or guest houses. Building an ADU is a great way to add value to a property. Done well, an ADU contributes function and flexibility while improving the beauty and style of your surroundings.