Modeled elevation reached by the flood having a 1-percent chance of being equaled or exceeded in any year.
Base Flood Elevation (BFE) is the modeled water-surface elevation reached by the flood having a 1 percent chance of being equaled or exceeded in any year.
The base flood is also commonly called the 100-year flood, but the event can occur more than once within a century.
BFE provides an elevation reference for comparing a building and surrounding ground with the mapped base-flood level. That comparison can affect floodplain construction requirements, insurance information, and FEMA map-change requests.
For a mortgage borrower disputing an SFHA result, BFE may be compared with surveyed building and ground elevations on an Elevation Certificate. The numbers must use compatible vertical datums; comparing values from different reference systems can create a false conclusion.
Borrowers may see BFE on a Flood Insurance Rate Map, Flood Insurance Study, elevation certificate, appraisal addendum, survey, insurance application, or FEMA letter-of-map-change package.
The lender’s standard flood determination usually focuses on whether the building is in the SFHA. A BFE becomes especially relevant when the map or building location is disputed, when a property is newly constructed in a mapped area, or when an insurer requests elevation data.
| Elevation | What it describes |
|---|---|
| Base Flood Elevation | Modeled height of the 1-percent-annual-chance flood |
| Lowest Adjacent Grade | Lowest ground touching the building |
| Highest Adjacent Grade | Highest ground touching the building |
| Lowest Floor Elevation | Height of the building’s lowest floor under the applicable measurement rules |
| Lowest Horizontal Structural Member | Important reference for certain coastal construction |
These terms are not interchangeable. The correct comparison depends on the zone, building type, policy, and purpose of the document.
BFE is an elevation relative to a stated vertical datum, not a universal depth above the floor or ground. To estimate a height difference, two elevations using the same datum must be compared.
For example, a BFE of 112 feet and a surveyed lowest-adjacent-grade elevation of 114 feet indicate a 2-foot elevation difference under the shared datum. The numbers do not mean the modeled flood is 112 feet deep.
A house near an SFHA boundary has a mapped BFE of 108 feet. A licensed surveyor documents the relevant natural-ground elevation at 110 feet using the same datum. The owner may use the professional evidence in a FEMA map-amendment request. The surveyor supplies measurements; FEMA decides whether to issue the map determination.
A Flood Zone is a mapped hazard category. BFE is a modeled water-surface elevation shown in certain zones.
An elevation certificate records actual building and site measurements. BFE is one reference value that may appear on the certificate.
A Special Flood Hazard Area is the mapped area exposed to the base flood. BFE expresses the modeled flood height where detailed information is available.
A Letter of Map Amendment is FEMA’s official determination. BFE and surveyed elevations may support the request but do not replace the letter.