What is Base Flood Elevation (BFE)?

FEMA determines BFE through comprehensive engineering studies called Flood Insurance Studies (FIS). These studies use hydrologic and hydraulic modeling to simulate how water would flow and accumulate during a base flood event. The process considers multiple data inputs to produce accurate flood elevation predictions.

The resulting BFE values are published on the community's FIRM panels. Along rivers and streams, BFE is shown as elevation values along cross-section lines that traverse the floodplain. In coastal areas, BFE accounts for both storm surge and wave action, resulting in higher values in V zones compared to A zones at similar elevations.

The relationship between your building's lowest floor elevation and the BFE is one of the most significant factors in determining your flood insurance premium. Under both the traditional NFIP rating system and Risk Rating 2.0, being above or below the BFE creates a dramatic difference in what you pay.

For a full breakdown of insurance costs by zone, see our Flood Insurance Cost Guide.

In communities that participate in the NFIP, local floodplain management ordinances require that new construction and substantial improvements in the SFHA meet specific standards relative to the BFE. These requirements are designed to reduce flood damage and protect lives and property.

• The lowest floor of residential buildings must be constructed at or above the BFE. Many communities require one or more feet of freeboard above the BFE for additional safety.
• Non-residential structures may use floodproofing techniques as an alternative to elevation, provided they are certified to be watertight to at least the BFE level.
• Areas below the BFE in elevated structures must use flood-resistant materials and include flood openings (vents) to allow water to equalize pressure and prevent structural failure.
• Manufactured homes in SFHAs must be elevated to the BFE on a permanent foundation with proper anchoring to resist flotation and lateral movement.
• In V zones, structures must be elevated on pilings or columns with the bottom of the lowest horizontal structural member at or above the BFE.

An Elevation Certificate (EC) is a critical document that records the elevation of a building's key features relative to the BFE. Prepared by a licensed surveyor, engineer, or architect, the EC provides the precise measurements needed to accurately rate a flood insurance policy and to verify compliance with floodplain regulations.

The Elevation Certificate documents several important measurements, including the elevation of the lowest floor, the top of the bottom floor, the lowest adjacent grade, the highest adjacent grade, and any attached garage floor elevation. By comparing these measurements to the BFE shown on the FIRM, your insurance agent can determine the correct premium for your property.

If your property sits above the BFE and you do not have an Elevation Certificate, investing in one (typically $300-$600) can save you significantly on your annual flood insurance premium. The cost of the EC is often recovered within the first year through lower premiums.

Two elevation measurements are frequently discussed in flood zone contexts: Base Flood Elevation and Lowest Adjacent Grade. Understanding the difference between them is important for insurance rating and for determining whether a property may qualify for a map change.

When the LAG is at or above the BFE, the property may qualify for a Letter of Map Amendment (LOMA) to be removed from the SFHA, since the natural ground elevation is sufficient to keep the building above the base flood level.

Zone AE is the most common SFHA designation and is specifically defined as an area subject to the 1% annual chance flood where Base Flood Elevations have been determined. The "E" in AE stands for "elevation determined," distinguishing it from Zone A, where no detailed study has been performed and BFEs are not available.

Having a BFE in Zone AE provides several advantages for property owners. It allows for precise insurance rating based on the actual difference between the building elevation and the flood elevation, rather than relying on approximate rates. It also establishes clear construction standards for new buildings and substantial improvements, and it enables property owners to determine whether they may qualify for a LOMA.

If your property is in Zone A (without a BFE), you may want to request that your community petition FEMA for a detailed study, or you can commission a private engineering study to establish approximate BFE values. Having this data can help you obtain a more favorable insurance rate and understand your true flood risk more precisely.