What Is Base Flood Elevation (BFE)? Definition and Why It Matters

Base Flood Elevation, or BFE, is the height to which floodwater is expected to rise during a flood with a 1% annual chance of occurring, the flood FEMA maps are built around. It's measured in feet above a fixed reference point, not as a depth of water, and it's one of the most important numbers in flood insurance because it's the line everything else gets compared against.

This article covers what BFE actually means, where to find your property's BFE, why your lowest floor's height relative to that number matters, and the basic idea behind freeboard.

What Base Flood Elevation Actually Means

BFE is a reference elevation, not a water depth. It represents how high floodwater is expected to reach during the flood used to define a Special Flood Hazard Area, commonly described as having a 1% annual chance of happening in any given year. A home near the coast and a home along a river can both have a BFE; the number is specific to that property's location and the flood study behind the map covering it.

A BFE is not assigned everywhere. Some areas, including Zone D and parts of Zone A without a detailed study, don't have a published BFE at all, which is one reason an elevation certificate and a flood map don't always tell the full story on their own.

Where to Find Your Base Flood Elevation

There are two main places a BFE shows up:

• The FEMA flood map (FIRM) for your property. In zones where a detailed study was completed, the map or its supporting data will show the BFE for that area, sometimes as a contour line, sometimes as a specific figure tied to a zone designation like AE.
• Item B9 on an elevation certificate. If a surveyor has completed an elevation certificate for the property, Item B9 lists the BFE used for that certificate, taken from the flood map in effect at the time. Item B8, next to it, shows which flood zone that BFE came from.

If you're comparing a BFE from a flood map to one on an elevation certificate, check that both come from the same map revision. Flood maps get updated, and a BFE that was accurate when a certificate was issued can be out of date if the map has changed since.

Why Your Lowest Floor Relative to the BFE Matters

The single comparison that drives much of how a flood policy gets underwritten is simple: how does the elevation of your building's lowest floor compare to the BFE for that property?

• Lowest floor above the BFE generally means the building has some built-in protection against the flood the map is based on.
• Lowest floor at or below the BFE generally means the building would take on water during that same flood, which is the scenario underwriters are most focused on.

This is exactly what Item C2.a on an elevation certificate is used for: it records the elevation of the lowest floor so it can be compared directly against the BFE in Item B9. The gap between those two numbers, whether positive or negative, is one of the biggest factors in how a flood property gets rated.

Freeboard: Building a Margin Above the BFE

Freeboard is simply extra height built in above the BFE, a margin of safety rather than meeting the minimum. Some communities require new construction or substantially improved buildings to be built a set number of feet above the BFE, which is their local freeboard requirement.

Freeboard matters because the BFE represents a specific flood, not the worst flood that could ever happen. A building with several feet of freeboard above the BFE has more room before floodwater reaches its lowest floor than a building built right at the minimum.

Common Mistakes People Make With Base Flood Elevation

• Confusing BFE with water depth. BFE is an elevation above a fixed reference point, not a measurement of how deep the water gets at the building.
• Assuming every property has a published BFE. Zone D and some unstudied parts of Zone A don't have one.
• Using a BFE from an outdated map. Flood maps get revised, and an old certificate may reference a BFE that no longer matches the current map.
• Overlooking freeboard when building or renovating. Meeting the BFE exactly leaves no margin if the next flood runs even slightly higher than the mapped prediction.

Pro Tips from Sterling Flood Underwriters

Check the map revision date against your certificate date. A BFE from years ago may not match the current flood map for that property.

If you're building or renovating, ask your local floodplain administrator about freeboard requirements before you start. It's far easier to build in extra height than to add it later.

Get a Quote

Knowing your BFE and how your lowest floor compares to it gives an underwriter real numbers to work with instead of assumptions. Get a flood insurance quote from Sterling Flood.

Frequently Asked Questions

Does every property have a Base Flood Elevation?

No. Properties in Zone D and some parts of Zone A without a detailed flood study don't have a published BFE.

Where exactly does Item B9 come from?

Item B9 on an elevation certificate is taken from the FEMA flood map in effect at the time the certificate was completed, specifically the BFE for that property's location.

What does it mean if my lowest floor is below the BFE?

It generally means the building would take on water during the flood the map is based on, which is a major factor in how a flood policy is underwritten.

Is freeboard required everywhere?

No. Freeboard requirements are set locally, so whether extra height above the BFE is required depends on the community's own building and floodplain regulations.