Base Flood Elevation vs Design Flood Elevation

Base Flood Elevation vs Design Flood Elevation Definitions

(Last Updated On: December 4, 2019)

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

 

Flood Insurance Rate Map FIRM

Flood Insurance Rate Map FIRM Indicates Base Flood Elevations

 

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

 

NAVD 88

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.

 

Zoning Drawings Showing BFE & DFE

One of our projects Approved NYC Zoning Drawings Showing BFE & DFE for a Concrete House in the Flood Zone

 

Photo of complete House from drawings above

House In The Flood Zone

Concrete House In The Flood Zone built above the DFE

 

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.

 


Thank you for reading our blog post on DFE and BFE Definitions.

I hope this was helpful. Please leave questions and comments below. If you would like to speak with an architect you can Contact Fontan Architecture directly.

 

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