What is Base Flood Elevation (BFE)? Zoning Definition
The computed elevation to which floodwater is expected to rise during a 100-year flood event, as determined by FEMA, used as the baseline for floodplain construction requirements.
Base Flood Elevation (BFE) is the height that floodwaters are predicted to reach during a base flood — the flood that has a 1% chance of occurring in any given year, commonly called the 100-year flood. FEMA determines BFEs through engineering studies and publishes them on Flood Insurance Rate Maps (FIRMs). The BFE is expressed as an elevation above sea level (for example, 25 feet NAVD88) and serves as the regulatory benchmark for construction in flood-prone areas.
Local floodplain ordinances require that the lowest floor of new residential buildings in high-risk flood zones be constructed at or above the BFE. For commercial buildings, the requirement is typically to elevate or floodproof to the BFE. Many communities go further and require freeboard — an additional height of one to three feet above the BFE — to provide a margin of safety against floods that exceed predictions.
The BFE directly affects construction costs and building design. A property with a BFE significantly above the existing ground level may need to be built on pilings, raised foundations, or fill material. The higher the required elevation, the more expensive the foundation work. The BFE also determines flood insurance premiums: buildings with their lowest floor below the BFE pay substantially higher premiums than those built above it.
If you are planning to build or renovate in a flood zone, your first step should be to determine the BFE for your property by checking the FEMA FIRM or contacting your local floodplain administrator. An elevation certificate, prepared by a licensed surveyor, documents the elevation of your structure relative to the BFE and is essential for obtaining flood insurance and building permits.
Related Terms
Flood Zone
A geographic area identified by FEMA on a Flood Insurance Rate Map (FIRM) that indicates the level of flood risk, which affects building requirements, insurance obligations, and development restrictions.
FEMA
The Federal Emergency Management Agency is the U.S. government agency responsible for mapping flood hazard areas, administering the National Flood Insurance Program, and coordinating disaster response and recovery.
Freeboard
An additional height requirement above the Base Flood Elevation that a community adopts to provide an extra margin of safety for buildings in flood-prone areas.