An Accessory Dwelling Unit (ADU), also known as in-law units, second units, cottages, 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.

A JADU is an additional, independent living unit created through the conversion of an existing bedroom in a single-family dwelling.

No. An accessory dwelling unit is habitable, while an accessory building is not (i.e. shed, covered porch, etc.). However, accessory buildings have the potential to be converted into an ADU, if it conforms to current ADU code requirements.

ADUs can be detached, attached or within the primary residence. Most ADUs are converted from existing storage or garage space.

In the City of San Mateo, one ADU or JADU is allowed per parcel.

ADUs cannot be rented for less than 30 consecutive days.

No. The property owner must record a deed restriction with the city of San Mateo restricting the sale of an ADU from the primary dwelling.

The Accessory Dwelling Unit Code (Section 27.19 Articles 1 and 2) of the City of San Mateo Zoning Ordinance, establishes the development regulations and other criteria that must be met to construct any type of ADU/JADU. See: See ADU/JADU Requirements. 

No, if the ADU meets exemptions from parking requirements (living within a ½ mile of transit stop, etc. SMMC 27.19.50 (k/5)). Remember, you can always contact the City Planning department to help your project conform to the SMMC code.

Yes. Any covered structure is counted as floor area (i.e. sheds, covered porches, etc.).

Yes, depending on the type of ADU. Please contact the SMC Fire Department at fire@smcfire.org or (650) 522-7900 

Yes, for both ADU and JADU.

They are required for ADUs, but not JADUs.

Property taxes are assessed by the County of San Mateo Assessor’s Office. Like other development projects in the City, the County collects information from the City when building permits are issued to a property. Please contact the County Assessor’s Office for more information about how the information is used.

An unregistered ADU cannot be registered until it fulfills current ADU city standards in the SMCC code i.e. parking, setbacks, facility standards etc. Unregistered ADUs are subject to code enforcement.

Check with the Building Division to see if your property has past building permits for a garage. If none are found, you will need to conform to the SMMC Building and Planning code and then apply for a garage permit with the Building Division.

The City of San Mateo recommends using the Peninsula Builders Exchange Construction Finder or call 650-591-4486.

You may contact our Planning and Building staff by email, phone, or by visiting our counter for further questions on your project. 

General Zoning Inquiries:

Email: planning@cityofsanmateo.org

Call Planner on Duty: (650) 522-7212

Planning Counter Hours: Monday, Wednesday, Thursday, Friday 8:00am - 4:45pm and Tuesday 12:30pm - 4:45pm

Building Permit Application and Fee Inquiries:

Building Counter Line: (650) 522-7172

Building Code Consultation (Building Plan Checker) Hours: Monday through Friday 9:30am - 11:30am

Fire Prevention Inquiries:

Justin Ho: (650) 522-7940

Fire Code Consultation Hours: Monday through Friday 9:30am-11:30am

Parks and Recreation Inquiries:

Call (650) 522-7400

Heritage Tree Preservation Inquiries:

Call (650) 522-7420