Jurisdiction ADU / Second Unit Standards Summary

Learn more about specific ADU regulations in each San Mateo County city. Click here to download a table summary of standards in all in 21 jurisdictions (Excel version available here).

Atherton

ADUs can be built in all residential zones. There is no minimum required lot size and the maximum ADU size is 1,200 square feet. One parking space is required unless state exemptions are met. Additional square footage is permitted in the main dwelling if an ADU is included. Full information here.

Contact: Lisa Costa Sanders – This email address is being protected from spambots. You need JavaScript enabled to view it., 650.572.0544

Belmont

ADUs can be built in all residential zones. There is no minimum required lot size and the maximum ADU size is 800 square feet but not to exceed 50% of the primary dwelling if attached. Belmont reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: Planner on Duty – 650.595.7478

Brisbane

ADUs can be built in zones R-1 and R-BA. There is no minimum required lot size. The maximum ADU size is 1,000 square feet. No additional parking is required. Brisbane reports they are taking steps to actively promote and encourage the construction of ADUs .Full information here.

Contact: Community Development Department – 415.508.2120, This email address is being protected from spambots. You need JavaScript enabled to view it.

Burlingame

ADUs can be built in all residential zones. A minimum lot size of 6,000 square feet is required. The maximum ADU size is 640 square feet. Burlingame reports they are taking steps to accommodate the construction of ADUs. Full information here.

Contact: Erika Lewit, Senior Planner – This email address is being protected from spambots. You need JavaScript enabled to view it., 650.558.7250

Colma

ADUs can be built in residential zones R, G (caretaker units), C (single family residences only), and RS (within existing footprint only). The maximum ADU size is 800 square feet. One parking space is required unless state exemptions are met. Full information here.

Contact: Colma Planning Department – 650.757.8888

Daly City

ADUs can be built in all residential zones with a single-family dwelling. There is no minimum required lot size. The maximum ADU size is 1,200 square feet for detached units; there is no limit for attached units. Full information here.

Contact: Michael VanLonkhuysen – 650.991.8158

East Palo Alto

ADUs can be built in all residential zones, including sites with multifamily buildings. Lots must be at least 5,500 square feet for an attached ADU and at least 7,500 square feet for a detached ADU. The maximum ADU size is 700-1,000 square feet depending on lot size. One parking space is added to the house requirement with the addition of an ADU unless state exemptions are met. East Palo Alto reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: Guido Persicone, Planning and Housing Manager – This email address is being protected from spambots. You need JavaScript enabled to view it. – 650.853.3195

Foster City

ADUs can be built in residential zones R-1, R-1/PD, and R-2. Lots must be at least 5,000 square feet and have a single-family dwelling. ADUs can be between 150-640 square feet. One parking space is required unless state exemptions are met. Full information here.

Contact: Timothy Maier, Associate Planner – 650.286.3237

Half Moon Bay

ADUs can be built in all residential zones and mixed-use zones on parcels developed with a single-family dwelling. There is no minimum required lot size. Minimum ADU size is 150 square feet and maximum ADU size is 700 square feet. The City is located entirely within the California Coastal Zone and as such, some of the State requirements do not apply. Half Moon Bay reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: Community Development Department – 650.726.8270

Hillsborough

ADUs can be built in all residential areas. There is no minimum required lot size. Maximum ADU size is 1,400 square feet. Parking is required unless state exemptions are met. Hillsborough reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: Planning Department – 650.375.7422

Menlo Park

ADUs can be built in all single-family residential zones with a minimum lot size of 6,000 square feet. The maximum ADU size is 640 square feet but not to exceed 50% of the primary dwelling if attached. One parking space is required unless state exemptions are met. Full information here.

Contact: Planning Department – 650.330.6702 – This email address is being protected from spambots. You need JavaScript enabled to view it.

Millbrae

Millbrae does not have an ordinance governing ADUs, so state law applies. ADUs can be built in all residential zones. There is no minimum required lot size and the maximum ADU size is 1,200 square feet but not to exceed 50% of the primary dwelling if attached. Full information here.

Contact: Planning Division – 650.259.2341

Pacifica

ADUs can be built in all residential areas with a single-family dwelling. There is no minimum required lot size. Maximum ADU size is 1,200 square feet; for attached ADUs the primary dwelling must be at least 850 square feet and the ADU cannot exceed 50% of the primary dwelling. Parking is required unless state exemptions are met. Full information here.

Contact: Christian Murdock, Senior Planner – 650. 738.7341, This email address is being protected from spambots. You need JavaScript enabled to view it.

Portola Valley

ADUs can be built in residential zones RE, R-1, and M-R. The minimum required lot size is 1 acre. Maximum ADU size is 1,000-1,500 square feet (depending on the zoning district). Parking is required unless state exemptions are met. Portola Valley reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: Debbie Pedro, Planning Director – 650.851.1700 x 218, This email address is being protected from spambots. You need JavaScript enabled to view it.

Redwood City

ADUs can be built in all residential zones with a single-family dwelling. There is no minimum required lot size. Maximum ADU sizes range from 700 to 900 square feet, depending on the lot size. Redwood City reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: Diana O’Dell, Principal Planner – This email address is being protected from spambots. You need JavaScript enabled to view it.This email address is being protected from spambots. You need JavaScript enabled to view it., 650.780.7236

San Bruno

ADUs can be built in all residential zones with a single-family dwelling. The lot must be big enough to meet lot coverage, setback and FAR requirements (likely at least 2,500 square feet). Minimum ADU size is 150 square feet and maximum ADU size is 640 square feet. Parking is required unless state exemptions are met (which is the case for most locations). San Bruno reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: Matt Jones, Assistant Planner – 650.616.7089

San Carlos

ADUs can be built in residential zones RS-3, RS-6, RM-20 and RM- 59 with a single-family dwelling. Maximum ADU size is 640 square feet for a detached ADU and 30% of total living area for an attached ADU. Parking is required unless state exemptions are met. San Carlos reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: Brittany Whitehill, Planning Technician – 650.802.4208, This email address is being protected from spambots. You need JavaScript enabled to view it.

City of San Mateo

ADUs can be built in all residential zones with a single-family dwelling. Maximum ADU size is 640 square feet. Parking is required unless exemptions are met. San Mateo reports they are taking steps to actively facilitate and encourage the construction of ADUs. Junior Accessory Dwelling Units (JADU) – conversion of an existing legally permitted bedroom within an existing single-family dwelling – is also allowed. Full information here.

Contact: 650.522.7212, This email address is being protected from spambots. You need JavaScript enabled to view it. 

County of San Mateo

ADUs can be built in all R zones except R-3 on the Bay side, and in zone R-1 on the coast side. A minimum lot size of 5,000 square feet is required. The maximum ADU size is 1,200 square feet. Parking is required unless state exemptions are met. San Mateo County reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: William Gibson – 650.363.1816

South San Francisco

ADUs can be built in some zones and wherever a single-family dwelling is constructed. There is no minimum required lot size. Maximum ADU size is 900 square feet for a detached ADU and up to 50% of the primary dwelling for an attached ADU. Parking is required unless state exemptions are met. South San Francisco reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: Rozalynne Thompson – 650.377.8535

Woodside

ADUs can be built in all residential zones. Maximum ADU size is 1,500 square feet. Parking is required unless state exemptions are met. Woodside reports they are taking steps to actively promote and encourage the construction of ADUs. Full information here.

Contact: Town Planning – 650.851.6796