▼

Accessory Dwelling Units

Show All Answers

1. What is an Accessory Dwelling Unit (ADU)?

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.

2. What is a Junior Accessory Dwelling Unit (JADU)?

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

3. Is an accessory dwelling unit the same as an accessory building?

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.

4. Where can I put an ADU on my property?

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

5. How many ADUs can I add to my property?

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

6. Can I use my ADU for short-term rentals?

ADUs cannot be rented for less than 30 consecutive days.

7. Can I Sell my ADU?

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.

8. What are the requirements for an ADU/JADU?

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. 

9. Do I need to provide parking for my ADU?

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.

10. Will the ADU count towards the density/floor area ratio of my property?

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

11. Is the ADU required to have fire sprinklers?

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

12. Is a Building Permit required for an ADU/JADU?

Yes, for both ADU and JADU.

13. Is a Discretionary Permit required for an ADU/JADU?

They are required for ADUs, but not JADUs.

14. Will my property taxes increase with an Accessory Dwelling Unit?

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.

15. What if I currently have an unregistered ADU?

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.

16. How do I know if my garage was built legally?

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.

17. Can the City help me find a licensed professional? (i.e. architect, contractor, engineer, designer, etc.)

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

18. If I have questions about the ADU Code Ordinance what can I do?

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