The Base Flood Elevation (BFE) is an elevation indicated on the Preliminary Flood Insurance Rate Map defining the elevation of a potential flood. The Design Flood Elevation (DFE) uses the BFE in order to determine the appropriate elevation for construction of new structures within a flood zone.
Base Flood Elevation vs Design Flood Elevation
Base Flood Elevation Definition (BFE)
The Base Flood Elevation is the elevation of flood water rise during the “base flood”. These elevations are indicated per location within a flood zone on the Flood Insurance Rate Maps or FIRMS. The BFE is used in determining the appropriate Design Flood Elevation for new construction. Additionally, the difference between a building’s BFE and actual elevation will affect the insurance rates.
The Base Flood Elevation is most commonly referred to as the BFE.
BFE vs DFE
Design Flood Elevation Definition (DFE)
The Design Flood Elevation or DFE is the elevation to be used for determining the elevation of building elements in new construction.
The Design Flood Elevation is most commonly referred to as the DFE.
DFE Calculation Example:
As per the NYC Building Code, the DFE for a single or two family house is BFE + 2. You would need to first determine your BFE. This can be done by checking the Flood Insurance Rate Map for your location. Lets assume the BFE is 9.
If DFE = BFE +2 and if the BFE is 10, then:
DFE = 9 + 2
DFE = 11
The current standards is that all Flood Elevations are based on NAVD88, which is the North American Vertical Datum of 1988.
Planning and Building in the Flood Zone
The BFE and DFE must be figured out before beginning even a preliminary design for a property in the Flood Zone. All documents submitted to the Department of Buildings must show compliance with all applicable Flood Zone Codes.
Photo of complete House from drawings above
Base Flood Elevation vs Design Flood Elevation Definitions
As an architect, I study Building and Zoning Codes closely, but these are complicated and quite involved issues. In this article, we reviewed some of the basic concepts with regards to the Base Flood Elevation and Design Flood Elevation definitions. This post does not assume to cover every possible issue or condition, but provide a general overview of the topic.
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This post was written by Jorge Fontan AIA a Registered Architect and owner of New York City architecture firm Fontan Architecture. Jorge Fontan has earned 3 degrees in the study of architecture including two degrees from the City University of New York and a Masters Degree in Advanced Architectural Design from Columbia University. Jorge has a background in construction and has been practicing architecture for 15 years where he has designed renovations and new developments of various building types.