Base Flood Elevation (BFE) and Its Importance

In the world of flood insurance and floodplain management, the Base Flood Elevation (BFE) is perhaps the most critical metric used by agents, surveyors, and engineers. The BFE represents the elevation to which floodwater is anticipated to rise during the "base flood." The base flood is defined as a flood having a one percent (1%) chance of being equaled or exceeded in any given year.

While many consumers mistakenly refer to this as a "one-hundred-year flood," insurance professionals must understand that this is a statistical probability, not a timeline. A structure can experience multiple base floods within a single decade. The BFE is a regulatory requirement used by the National Flood Insurance Program (NFIP) to determine building standards and calculate insurance premiums. For a deeper dive into how this fits into the broader insurance landscape, see our complete Flood exam guide.

The BFE is established through hydraulic and hydrologic analyses and is depicted on Flood Insurance Rate Maps (FIRMs). These maps divide areas into different zones based on risk. In Special Flood Hazard Areas (SFHAs), which include zones starting with the letters 'A' or 'V', the BFE is the regulatory benchmark.

• Zone AE: Areas with a determined BFE, typically used for inland or riverine flooding.
• Zone VE: Coastal high-hazard areas where the BFE also accounts for additional wave action (velocity).
• Zone AH: Areas of shallow flooding (usually ponding) where BFEs are established.

Without an established BFE, it is difficult for underwriters to accurately assess the risk of a property. When preparing for your certification, you can practice identifying these zones using our practice Flood questions.

To determine how a building relates to the BFE, the NFIP requires an Elevation Certificate (EC). This document, completed by a licensed land surveyor, engineer, or architect, provides the exact elevation of various parts of the building, including the Lowest Floor Elevation (LFE).

The difference between the BFE and the LFE is the primary driver of flood insurance rates. If a building's lowest floor is three feet above the BFE, it is statistically much less likely to suffer a loss than a building sitting two feet below the BFE. This height difference is often referred to as Freeboard. Many communities require freeboard as an added safety margin in their local building codes, which can lead to Community Rating System (CRS) discounts for all residents in that area.

The BFE isn't just for rating; it triggers the Mandatory Purchase Requirement. If a structure is located in an SFHA and the community participates in the NFIP, any federally backed mortgage requires flood insurance. If the BFE is higher than the lowest floor, the lender sees an unacceptable level of risk.

Property owners can mitigate this risk by:

• Elevating the structure: Raising the entire building on piers or piles so the LFE is above the BFE.
• Flood Venting: Installing hydrostatic vents in crawlspaces to allow water to flow through, which may change how the 'lowest floor' is defined for rating purposes.
• Dry Floodproofing: Making a non-residential structure watertight below the BFE.