An Accessory Dwelling Unit (ADU)

Accessory dwelling units (or “granny units,” “in-law units,” and various other names) are smaller units built on the same property as, or attached to, an existing primary residence. The County of San Mateo regulates the production of second units in the unincorporated areas of the County only (those areas that are not in the jurisdiction of incorporated cities). Find the regulating ordinance linked below.

Non-Coastal Zone

Coastal Zone

How to Apply