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Floodplain maps

Floodplain maps

King County, Washington

On August 19, 2020 new FEMA flood maps became effective in King County.

If you have questions about the flood map updates, please contact the River and Floodplain Management Section at 206-477-4812 or Please include your full name, full property address, parcel number (if available), contact information (including mailing address, email address, and phone number), and questions or specific requests.

FEMA floodplain information availability

King County iMap
Navigate, view and print custom maps using a wide variety of data within King County including: Parcels, FEMA floodway, FEMA floodplain boundaries, FEMA area with reduced risk due to levee, FEMA FIRM panels, and FEMA cross-sections.

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

Elevation Certificates, Letter of Map Amendments (LOMA) and Revisions (LOMR-F) mapping application
Navigate, view and print available Elevation Certificates, Letter of Map Amendments (LOMAs) and Letter of Map Revisions Based on Fill (LOMR-F).

An Elevation Certificate is a form created by FEMA under the National Flood Insurance Program as a compliance and insurance tool within federally mapped floodplains. King County has elevation certificates for many properties within the SFHA. Flood hazard information contained on elevation certificates may be out of date as map changes have occurred. Elevation Certificates may contain errors, omissions of inaccuracies.

A Letter of Map Amendment (LOMA) is an official amendment, by letter, to an effective National Flood Insurance Program ;map. A LOMA establishes a property's location in relation to the Special Flood Hazard Area (SFHA). LOMAs are usually issued because a property has been inadvertently mapped as being in the floodplain, but is actually on natural high ground above the base flood elevation.

A Letter of Map Revision Based on Fill (LOMR-F) is FEMA's modification of the Special Flood Hazard Area (SFHA) shown on the Flood Insurance Rate Map (FIRM) based on the placement of fill outside the existing regulatory floodway.

Flood map information for realtors, lenders and insurance agents
Information specific to the real estate, lending, and insurance industry.

Contact the River and Floodplain Management Section
206-477-4812 or

Staff can provide assistance with:

  • Confirming if a property is located within a Federal Emergency Management Agency (FEMA) mapped Special Flood Hazard Area (SFHA), or flood prone area identified by King County.
  • Provide flood insurance rating information such as FIRM zone, panel number, suffix, panel date and index date.
  • Provide FEMA elevation certificates if available.
  • Determine what regulatory provisions may apply to a specific property.
  • If available, provide information on past flood damage to a property.

Development in Floodplains

All development in a mapped floodplain needs a permit, and buildings, in particular, must demonstrate compliance with King County Code. Managing development in floodplains is a core responsibility of King County as part of our participation in the National Flood Insurance Program. Proper permitting means that flood insurance will remain available to all residents of unincorporated King County.

All development proposals in unincorporated King County must go through the Department of Local Services- Permitting to apply for a floodplain development permit.

Floodplain development standards are part of the Critical Areas chapter of King County Code 21A.24. Sections 21A.24.230 through 21A.24.272 establish the requirements for floodplains, including coastal high hazard areas. Some of the key pieces of floodplain development standards are the following requirements:

  • New or substantially improved homes be elevated to 3 feet above the 100-year flood elevation.
  • No development will occur in areas where the 100-year flood depths are greater than 3 feet and where the velocity of floodwaters are greater than 3 feet per second.
  • Development in the floodway will provide certification that it will not cause a rise in 100-year flood elevations for any other property.
  • Any development that includes fill will provide compensatory storage to offset the loss in flood storage.
  • In coastal flood hazard zones, buildings are only allowed to be built on piers or posts.

All buildings must have a FEMA Elevation Certificate completed by a licensed surveyor that shows compliance with the King County Code.

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