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The Flood Disaster Protection Act of 1973 and the National Flood Insurance reform Act of 1994 make the purchase of flood insurance mandatory for federally backed mortgages on buildings located in the 100-year floodplain mapped on a Flood Insurance Rate Map (FIRM).

To determine if a property is located in the mapped 100-year floodplain, enter an address or property tax lot number into King County’s Interactive Mapping Tool: iMap. If an address or tax lot number is not available, simply zoom in on a specific area or parcel to determine its location in the floodplain.

The iMap application can produce maps displaying aerial imagery, parcel boundaries with overlays of floodplain, floodway and other natural hazards. Data used in iMap reflect best available science, including new flood studies and map amendments, and is not limited to the published Flood Insurance Rate Maps. Hydrographic layers for the 100-year floodplain, floodway and channel migration zones can be added to the map to inform the user if this property is located in a floodplain and whether the mandatory flood insurance purchase would likely be required.

NOTE: The mandatory flood insurance purchase requirement only applies to properties within FEMA-designated floodplains. However, owners of properties located within a floodplain designated through iMap are strongly encouraged to consider flood insurance coverage.

Staff from the River and Floodplain Management Section are available to assist with the following flood map information at 206-477-4727:

  • Whether a property is located within a FEMA mapped Special Flood Hazard Area (SFHA) or flood prone area identified by King County.
  • Flood insurance rating information such as FIRM zone, panel number, suffix, panel date, index date and regulatory base flood elevation.
  • FEMA elevation certificates if available. King County has elevation certificates for many properties within the SFHA.
  • Regulatory provisions that may apply to the property in question.
  • If available, whether the property has ever suffered any flood damage.

King County Code >> Critical Areas (Acrobat PDF format)
County definitions and rules on development standards, restrictions, and requirements as well as permitted uses in King County floodplains and other sensitive areas. Codes pertaining specifically to floodplains can be found under sections 21A.24.230 to 21A.24.275 of this document.

FEMA Flood Map Service Center (external link)
The official online location to find all flood hazard mapping products created under the National Flood Insurance Program (NFIP).

For questions about the floodplain maps, please contact Ken Zweig, Program Manager, River and Floodplain Management Section.