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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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Accessory Dwelling Unit (ADU) - Conversion of an accessory building
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Accessory Dwelling Unit (ADU) - Addition on-top of Garage
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Accessory Dwelling Unit (ADU) - Addition on-top of Garage
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Accessory Dwelling Unit (ADU) - A half-converted detached garage/pool house
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Accessory Dwelling Unit (ADU) - A half-converted detached garage/pool house
Ready to get started?
- Find your zoning district - use our interactive Property Zone Look-Up Tool (interactive GIS map) or check the Zoning Map (.pdf)
- 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.
- Review the these additional requirements: ADU Parking Requirements, Utility Connection Requirements, and Deed Restriction
- Download related documents:
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.
Accessory Dwelling Unit (ADU) Municipal Code Requirements
The purpose of Chapter 27.19 - Article I is to set forth regulations to permit accessory dwelling units on residential zoned properties (R1-A, R1-B, R1-C, R2, R3, R4, R5, R4D, R5D, R6D and BMSP) with a single-family residential use. A parcel with a single-family residential use, may have only one accessory dwelling unit (ADU) or one junior accessory dwelling unit (JADU), but not both. (Ord. 2017-5 § 4)
Summary of ADU Requirements:
- Allowed in R1-A, R1-B, R1-C, R2, R3, R4, R5, R4D, R5D, R6D or BMSP zoning districts.
- One ADU per parcel.
- ADU cannot exceed 640 sf in Total floor Area including attic, stairs, and basement areas SMMC 27.19.04.
- Detached and attached ADUs, located in R1 and R2 zoning districts, must comply with height standards Height Requirements of 24x32 of the underlying zoning district SMMC 27.18.050 Building Height.
- Same architectural style as primary structure (i.e. material, finishes, colors, etc.) SMMC 27.19 (l).
- ADUs must have a separate exterior entryway, cooking facility and bathroom SMMC 27.19.050 (h/i).
- Meet Heritage Tree Standards.
- Meet Setback requirements for underlying zoning district (with exceptions to legally permitted garage conversions). Conversions cannot occupy more than 50% of the rear yard.
Junior Accessory Dwelling Unit (JADU) Municipal Code Requirements
The purpose of Chapter 27.19 - Article II is to set forth regulations to permit junior accessory dwelling units on one- and two-family residential zoned properties (R1-A, R1-B, R1-C, and R2). A parcel with an existing legally permitted single-family use may have only one accessory dwelling unit or one junior accessory dwelling unit, but, not both. (Ord. 2017-5 § 4)
Summary of Requirements
- Can be located in R1-A, R1-B, R1-C, and R2 zoning districts
- Cannot exceed 500 sf in total Floor Area.
- The junior accessory dwelling unit shall be constructed within the existing walls of an existing, legally permitted single-family dwelling unit and must include the conversion of an existing, legally permitted bedroom 27.19.110 (b).
- Must have interior and exterior entryway to primary residence 27.19.110 (f).
- No additional off-street parking is required for a JADU.
- Efficiency food preparation area 27.19.110 (g).