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Thurston County, Washington

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Community Planning and Economic Development

Building & Development in Special Flood Hazard Areas

Thurston County regulates new construction, and rebuilding after a flood for properties located in Special Flood Hazard Areas. 

How to Get Started 

  1. Check the county's online map to see if the project property is in a special flood hazard area. (see Find Out What You Can Do with a Property, steps 1-4). 
  2. If it is, check county records to see if a flood elevation certificate is already on file for the property. See instructions under Elevation Certificates below.
  3. Consider hiring a surveyor or engineer to do an elevation survey of the property to know if/where you may site a project before you apply for permits.

Allowed Construction (general information)

  • New construction may be allowed in some flood zones. Apply for Reasonable Use Exception first. If approved, then apply for permits. Details in county code14:38:050.
  • Manufactured home replacement allowed in same location with another of a similar size (per Thurston County Critical Areas Ordinance. Details in 14:38:050).
  • No new construction in floodways (per Federal Emergency Management Administration).
  • No new construction in flood plains (per Thurston County Critical Areas Ordinance).
  • No new construction in high groundwater flooding areas (per Thurston County Critical Areas Ordinance).
  • Home improvements –May be allowed. Depends on whether the improvements are due to a natural disaster or are discretionary, and whether they equal or exceed 50%* of the fair market value before any renovation occurred.
  • Existing Structure after natural disaster – If in floodplain may be repaired or replaced in existing footprint. If construction involves replacing 50%* or more of the structure, it is treated as a new structure in code.
  • Existing structures/ discretionary restoration or rebuilding, not due to natural disasters – Property owners may restore/rebuild existing structures in a floodplain for reasons other than a natural disaster -- provided the work occurs within the existing footprint and is less than 50%* the structure.  Any discretionary work that involves restoring or rebuilding 50% or more of the structure is treated as a new structure which -- in effect -- means that the work must occur outside the floodplain per Thurston County's Critical Areas Ordinance. 
  • *The 50% threshold is a FEMA requirement, and based on fair market value prior to the damage or reconstruction. Details in code chapter 14:38:050 linked below.

General Permit Requirements

  • See guide to getting permits after a flood. Detailed instructions will be in the permit application instructions, but generally you'll need:
    • Two (2) elevation certificates from licensed surveyor or engineer: 
      • Get the first one before you build to confirm vertical height requirement in relation to base flood elevation. (See if there is one already on file. Instructions in Elevation Certificates below). 
      • Get the second one after you build to measure height once the home is complete.
  • Conform to county building codes and requirements for construction in Special Flood Hazard Areas .
  • Proof of flood insurance for the home. Learn about flood insurance for properties in unincorporated areas of Thurston County.
  • Homeowner subscribe to the free county flood warning system by phone 360-754-3360 or online. 

Which County Codes May Apply

The county adopts FEMA (Federal Emergency Management Administration) maps, regulations, standards, buffer requirements, etc. Details in county codes related to flood areas: 

Elevation Certificates & Info for Surveyors 

  • Go to Permit Tracker and select Past Permit. Then enter permit, parcel or project number and select Document Type: Flood Elevation Certificates. If an elevation certificate was previously issued for a property, it will show up in the list.
  • If Thurston County does not have an elevation certificate on file for your property, you may need to hire a professional surveyor.
  • See the county's Elevation Certificate Instructions  
  • Check out county Flood Monuments & photos
  • Flood Insurance Rate Map Examples: panel map map legend.

Special Flood Hazard Areas ..

  • is the collective name, in county code, and on the county's online map for:
    • Flood of Record Monuments (click a triangle to see monument details.
    • Flood Zones FEMA
    • High Groundwater Hazard Areas 
  • Are considered any area mapped as Flood and Groundwater Hazard on a county map. Go to County Maps for map link and instructions.
  • Any area so described in county codes.
  • Subject to a base of one-hundred year flood (areas of special flood hazard are shown on a flood hazard boundary map or Flood Insurance Rate Map as Zone A, AO, A1-30, AE, A99, AH, VO, V1-30, VE, V).
  • Highest known recorded flood elevation. 
  • Important note: High water areas change as ground conditions change over time due to development or naturally occurring changes. County staff consult flood elevation certificates and photos of past floods to identify whether a property is within a Special Flood Hazard Area.

See Flood Area Diagram Drawings


If the market value of your home is found to be $100,000 and the repairs are estimated to cost $35,000 then the cost of repairs would be less than 50% of the market value of your home, therefore, you could continue with the repair of your home. However, if the market value of your home is $100,000 and the repair is estimated to cost $60,000 then the repair cost would exceed 50% of the market value of your home. If this is the case, the base flood elevation or BFE would have to be determined and if your lowest floor of your home is not at least 2-feet above the BFE you could not repair your home without first raising the lowest floor 2-feet above the base flood elevation. This is a requirement of both FEMA and the National Flood Insurance Program to help prevent future flooding to structures in a special flood hazard area.

Contact us

Tim Rubert, Floodplain Manager at 360-867-2123 or