There are many reasons that homeowners are adding ADUs to their backyard or above their garages.  For most homeowners, home improvements are a major expense, but ADUs can add both value to the property and also income which can help homeowners to afford their mortgages, utilities, taxes and other monthly bills.  Especially for older homeowners, additional income from an ADU can allow them to remain in their homes longer.

ADUs in California specifically can be sold separately from the main house, and there are no restrictions on renting them out for extra income, and homeowners associations are prohibited from preventing ADUs from being built.