San Mateo County, CA zoning map, flood zone and property lines by address
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Towns in San Mateo County: Daly City, San Mateo, Redwood City.
Flood zone by address
ParcelSheet reads FEMA's National Flood Hazard Layer at the lot: the zone, whether it is a high risk area where lenders ask for flood insurance, and the base flood elevation where FEMA lists one. FEMA's countywide study for San Mateo County has 147 FIRM panels, the newest effective April 2019; coastal V zones, where waves add to the flood, are mapped along its shore.
The official panel and any Letter of Map Amendment are at FEMA's Map Service Center. An elevation certificate for a San Mateo house comes from a licensed surveyor and is often on file with the county or city building office.
Property lines
The parcel outline, parcel number and mapped size come from the California county parcel layers (each county publishes its own), so a San Mateo lot shows the same lines the county assessor draws. San Mateo County covers about 287,106 acres of land and 187,110 acres of water.
Mapped lines are approximate. The San Mateo County assessor keeps the parcel record (San Mateo County website); a licensed surveyor sets the true corners.
Zoning
San Mateo County zones its unincorporated land, and Daly City, San Mateo, Redwood City each zone the land inside their limits. ParcelSheet shows the use the county assessor lists for the lot and links the county planning department for the district, the uses it allows and the lot size it needs.
ADU and guest houses
Under California's Planning and Zoning Law (Government Code Title 7, Division 1, starting at section 65000), local governments can allow an accessory dwelling unit on a lot with a house. Whether a San Mateo lot can add one depends on its district; the county planning department has the rule. ParcelSheet shows the mapped lot size and the ground's slope, the first two things the question turns on.
Septic and soil
ParcelSheet reads the USDA soil survey at the lot: the soil's name, its septic absorption rating and whether it is prime farmland. San Mateo County is soil survey area CA689, San Mateo County, Eastern Part, and San Francisco County, California, last updated September 2026, on Web Soil Survey.
A new or changed septic system in San Mateo County needs a permit from the San Mateo County environmental health department (under the State Water Resources Control Board OWTS Policy).
Setbacks
Setbacks in San Mateo County come from the zoning district: the front, side and rear distances a house must keep. ParcelSheet does not draw setback lines; the county zoning office gives them for the lot's district, and Daly City, San Mateo, Redwood City for land inside their limits.
Hazards that apply
- Storm surge. San Mateo County has coastal V zones on its FEMA map, so storm surge reaches its shore. The county's evacuation zones are on its emergency management site; ParcelSheet shows the FEMA zone and the 3 ft sea level rise map at the lot.
- Wetlands and wildfire. ParcelSheet shows the National Wetlands Inventory near a San Mateo lot and the Forest Service wildfire hazard rating at it.
Questions
Is my house in a flood zone in San Mateo County?
Type the address in the box above and ParcelSheet reads FEMA's flood zone at the lot's center. FEMA's countywide flood map for San Mateo County has 147 panels, the newest effective April 2019. A lender or insurer uses the official FIRM panel; FEMA's Map Service Center has it.
How do I find property lines in San Mateo County?
Open the California map, type the address, and the parcel outline from the San Mateo County assessor shows on the map with its parcel number and mapped size. Mapped lines are approximate; only a licensed surveyor sets the true corners.
What is my property zoned in San Mateo County?
Zoning in San Mateo County is set by the county for unincorporated land and by each city (such as Daly City, San Mateo) inside its own limits. ParcelSheet shows the use code the county assessor lists and links the office that sets the zoning; the planning office has the final word.
Can I build an ADU in San Mateo County?
Under California's Planning and Zoning Law (Government Code Title 7, Division 1, starting at section 65000), counties and cities can allow an accessory dwelling unit, and each sets its own rules. In San Mateo County ask the zoning office for the lot's district first; ParcelSheet shows the lot size as mapped so you can see the room you have.
Do I need a septic permit in San Mateo County?
Yes. A new or changed septic system in San Mateo County needs a permit from the San Mateo County environmental health department (under the State Water Resources Control Board OWTS Policy). ParcelSheet shows the USDA soil survey's septic rating at the lot, from survey area CA689 (San Mateo County, Eastern Part, and San Francisco County, California).
What can I build on 5 acres in San Mateo County?
Zoning in San Mateo County is set by the county for unincorporated land and each city inside its own limits (such as Daly City, San Mateo). The zoning district decides the uses, how many homes and the smallest lot it allows on 5 acres. ParcelSheet shows the lot size as mapped and the use code on the parcel record; the planning office has the district and its rules. See the San Mateo County website.
What are the residential setbacks in San Mateo County (2026)?
Setbacks in San Mateo County come from the zoning code of the county, or of the city when the lot is inside city limits: the front, side and rear distances depend on the lot's district. ParcelSheet does not draw setback lines or give a number it did not read; the zoning office gives them for the district. See the San Mateo County website.
Next to San Mateo County: Alameda County, Santa Clara County, Santa Cruz County.
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