What is a base flood elevation (BFE)?
Base Flood Elevation (BFE) is the official water-surface elevation that floodwaters are projected to reach during the base flood -- the 1% annual chance flood event. FEMA publishes BFEs on Flood Insurance Rate Maps (FIRMs) for high-risk zones like AE and VE. Your property's lowest floor elevation relative to the BFE directly affects your flood insurance premium: the higher you are above the BFE, the lower your expected premium.
But a general answer can't tell you YOUR risk -- the only way to know is to check your address.
Answered using FEMA National Flood Hazard Layer + US Census geocoding data.
How is BFE calculated?
FEMA engineers conduct hydrologic and hydraulic studies to model how water behaves during a flood that has a 1% annual probability. They account for the watershed area, channel geometry, friction, and other factors to compute the expected water surface elevation at points along the study area. These elevations are published on Flood Insurance Rate Maps (FIRMs) as BFE contours for Zone AE (riverine) and Zone VE (coastal). Not all high-risk zones have published BFEs -- plain Zone A uses approximate methods and does not carry a BFE.
Why your elevation relative to BFE matters
Under FEMA's Risk Rating 2.0 pricing approach, flood insurance premiums reflect individual property risk, including how your lowest floor elevation compares to the BFE. A structure with its first floor 2 feet above the BFE has much less expected flood damage than one at or below the BFE, and its premium reflects that lower expected loss. An Elevation Certificate, prepared by a licensed surveyor, documents your structure's elevations and is used by insurers to rate your policy more precisely.
What if my property is below the BFE?
A property below the BFE is at higher risk during the base flood event and will generally carry higher NFIP premiums under Risk Rating 2.0. Some properties built before FEMA's original Flood Insurance Rate Map was adopted for the community (pre-FIRM buildings) may qualify for certain rating methods. If your property is mapped below the BFE in error -- for instance, the survey data used by FEMA was outdated -- you may be able to correct it through a LOMA by demonstrating your true elevation using a current Elevation Certificate.
Sources
- FEMA Glossary: Base Flood Elevation (FEMA)
- FEMA Flood Zone Glossary (FEMA)