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 (per 44 CFR 60.3) 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 document that records the elevation of a building's key features relative to the BFE. It must be prepared by a licensed land surveyor, professional engineer, or architect who is authorized by their state or local jurisdiction to certify elevation data. 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.

When You May Need an Elevation Certificate

• Most local floodplain ordinances require an EC for any new building or substantial improvement in a high-risk flood zone. Your local building department will typically request one before issuing permits.
• If your lowest floor is above the BFE, an EC can document that and potentially reduce your premium. This is especially valuable when your building was constructed above the BFE but you have never had it formally surveyed.
• To remove your property from the SFHA through a Letter of Map Amendment, FEMA requires elevation data. An EC (or equivalent survey) is typically part of the LOMA application package.
• Buyers in SFHAs may request an EC to understand the actual flood risk and expected insurance cost before closing.

An Elevation Certificate typically costs $300 to $2,000, depending on your location and the complexity of the property. The cost is often recovered within the first year through lower premiums if the EC shows your building sits above the BFE.

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.

Freeboard is the additional height above the Base Flood Elevation that a community may require for new construction and substantial improvements. While the NFIP minimum standard requires building to the BFE, many communities adopt higher standards by adding a freeboard requirement on top of it.

Typical freeboard requirements range from 1 to 3 feet above the BFE. The extra height accounts for uncertainty in flood studies, potential future increases in flood risk from development or climate change, wave effects that may not be fully captured in the BFE, and debris carried by floodwater. Some states mandate freeboard statewide. Florida, for example, requires at least 1 foot of freeboard above the BFE for new residential construction.

Benefits of Building Above the BFE

• Each foot of elevation above the BFE significantly reduces flood insurance rates. A property built 2 or 3 feet above the BFE can save hundreds or even thousands of dollars per year compared to one built at exactly the BFE.
• Freeboard provides a margin of safety against floods that exceed the base flood, which is not uncommon. The 1% annual chance flood is a statistical estimate, not an upper limit.
• Properties built above the BFE are more attractive to buyers who factor in flood risk and ongoing insurance costs.
• Communities that adopt freeboard requirements earn credits under FEMA's Community Rating System (CRS), which lowers flood insurance premiums for all policyholders in the community.

Not all communities require freeboard, but FEMA strongly encourages it. Check with your local floodplain administrator to find out whether your community has adopted a freeboard requirement and how much additional elevation is needed above the BFE for new construction or substantial improvements.