San Mateo's Accessory Dwelling Unit Ordinance (Zoning Code Chapter 27.19) establishes the development standards and requirements for Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs). The approval process for a compliant ADU or JADU is ministerial, with only a building permit and related permits required. A planning application with public notification is not required for applications that meet the objective development standards of the ADU Ordinance.

What is an Accessory Dwelling Unit?

An Accessory Dwelling Unit (ADU) is accessory to a primary residence and has complete independent living facilities for one or more persons. An ADU can be attached or detached from the primary dwelling unit or converted from existing floor area. It is required to provide permanent provisions for living, sleeping, eating, cooking, sanitation. It must also meet other requirements as stipulated by applicable life and safety code requirements from the Building Division, Fire Department, and Public Works Department. An Accessory Dwelling Unit is different from an Accessory Building. Examples of Accessory Buildings include garden sheds, tool sheds, and workshops, per SMMC Chapter 27.70