Accessory Dwelling Unit (ADU) & Jr. Accessory Dwelling Unit (JADU)

San Mateo Municipal Code (SMMC) Chapter 27.19 - Articles 1 and 2 

This page summarizes key Planning, Building, Fire, and Public Works requirements. 

Note: The requirements summarized below are not inclusive. 
If you have specific questions for your project, please contact the appropriate department. 

What is an Accessory Dwelling Unit (ADU)?

An Accessory Dwelling Unit, also known as in-law units or granny units, is a smaller living unit on a property that has a single-family residence. An ADU is an attached or detached residential dwelling unit which provides independent living facilities for one or more persons, is accessory to the primary single-family residential dwelling unit, and includes permanent provisions for living, sleeping, eating, cooking facilities, and sanitation on the same parcel as the primary residential dwelling unit. SMMC: Chapter 27.19 Article 1

What is an Junior Accessory Dwelling Unit (JADU)?

A Junior Accessory Dwelling Unit (JADU) is an additional, independent living unit created through the conversion of an existing legally permitted bedroom in a single-family dwelling subject to defined standards in SMMC: Chapter 27.19 Article 2

Note: Accessory Dwelling Units differ from Accessory Buildings. SMMC: Chapter 27.70
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Contact Us 

Consultation Counter Hours:

Monday - Friday

9:30 a.m. - 11:30 a.m.


Planning Unavailable:


9:30 a.m. - 12:30 p.m.


Planning Division

Phone: (650) 522-7212



Building Division

Phone: (650) 522-7172



San Mateo Consolidated Fire

Phone: (650) 522-7940

Ready to get started?

  1. Find your zoning district - use our interactive Property Zone Look-Up Tool (interactive GIS map) or check the Zoning Map (.pdf)
  2. Review the ADU and JADU Municipal Code requirements - make sure you meet the proper Municipal Code requirements, a summary of each is listed in the tabs below.
  3. Review the these additional requirements: ADU Parking Requirements, Utility Connection Requirements, and Deed Restriction
  4. Download related documents:
  1. Find My Zoning District
  2. Review ADU Code Requirements
  3. Review JADU Code Requirements

Use our interactive 
Property Zone Look-Up Tool (interactive GIS map) or check the Zoning Map (.pdf)

  • Accessory Dwelling Units (ADU) can be located in R1-A, R1-B, R1-C, R2, R3, R4, R5, R4D, R5D, R6D or BMSP zoning districts.
  • Junior Accessory Dwelling Units (JADU) can be located in R1-A, R1-B, R1-C, and R2 zoning districts.