San Mateo County, CA Environmental Rules: Flood Zones (2026)
FEMA flood zone rules in San Mateo County, CA, also called floodplain regulations or special flood hazard area (SFHA) rules, determine flood insurance requirements and elevation standards for new construction.
Key Facts
- Scope
- Unincorporated county only, not the 20 cities
- Permit authority
- Director of Planning and Building
- Floodway rule
- Engineer no-rise certification required
- Coastal high hazard
- Structures must sit landward of mean high tide
- Storage ban
- No flammable/explosive materials in hazard areas
- Historic exception
- Streamlined exception for listed historic structures
- Penalty
- Misdemeanor plus public nuisance abatement
Summary
Unincorporated San Mateo County bars grading, filling, new construction or any other development in a mapped Area of Special Flood Hazard, Floodway or Coastal High Hazard Area until the Director of Planning and Building issues a development permit under Zoning Chapter 8.300, which applies only outside the county's 20 incorporated cities.
The areas of San Mateo County subject to flood discharge, flood or flooding, as established by Chapter 8.300 are hereby divided into Areas of Special Flood Hazards, Floodways and Coastal High Hazard Areas. Development located in Areas of Special Flood Hazards, which includes Floodways and Coastal High Hazard Areas, is required to meet applicable regulations of the County Subdivision Regulations and Building Regulations... 1. Areas Of Special Flood Hazard. A permit for development located in an Area of Special Flood Hazard may be issued in accordance with the procedures established in Section 6826 provided: (a) Structures are constructed so that the lowest floor is elevated to or above the regulatory flood-protection elevation. (b) The development is in compliance with applicable Standards of Construction contained in Section 8131... (c) The use is consistent with the General Plan and permitted by the zoning district in which the use is to be located or conducted, and all required permits and approvals are obtained.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 47).
Full Breakdown
300 applies only within the unincorporated territory of San Mateo County, not the county's 20 incorporated cities, each of which runs its own FEMA floodplain ordinance. The chapter is based on the Flood Insurance Study for the unincorporated areas prepared for FEMA, and no development may proceed on land it covers without full compliance. For an Area of Special Flood Hazard, a permit issues only if the lowest floor is elevated to or above the regulatory flood-protection elevation, the project meets the Building Regulations construction standards in Sections 8131, 8132 and 8309, and the use is consistent with the General Plan and the applicable zoning district.
Inside a designated floodway, no fill, new construction or substantial improvement may occur unless certified as producing no increase in flood levels during a base flood discharge. Coastal High Hazard Area structures must stand landward of the mean high tide, and man-made alteration of sand dunes that would increase flood damage is prohibited outright. Storage of flammable, explosive or otherwise injurious materials is banned in any Area of Special Flood Hazard. Applications go to the Planning and Development Division and must include site plans, proposed structure elevations and floodproofing data.
The Director of Planning and Building may grant a streamlined exception for reconstruction of a structure listed on the National Register of Historic Places, the California Historical Landmarks Program or the County's own historic inventory, bypassing the standard exception-review criteria used for other projects.
Violations & Fines
Any violation of Chapter 8.300, including building without a development permit or below the required elevation, is a misdemeanor punishable under San Mateo County Ordinance Code Sections 1200 through 1203. Noncompliant structures and uses are separately declared a public nuisance, and the County may bring abatement, removal or injunction proceedings; these remedies are cumulative, not exclusive, so both criminal and civil enforcement can run at once.
Frequently Asked Questions
Does Chapter 8.300 apply inside Redwood City, San Mateo or other cities?
What does building in a mapped floodway require?
Can a historic home get an exception from these standards?
Can I store fuel or chemicals on flood-hazard property?
Sources & Official References
Other rules in San Mateo County
California rules heatmap·Compare San Mateo County to another location·View the California environmental rules overview
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