With funding from the San Mateo County Housing Innovation Fund, the University of California at Berkeley’s Center for Community Innovation conducted wide-ranging research on 2nd Units a.k.a. “Granny Flats”, “Backyard Cottages”, “Accessory Dwelling Units” or “ADUs”. The reports below will help inform public policy and programs to promote the construction of these units as an innovative way to create new housing opportunities in existing single family neighborhoods.