FEMA Technical Bulletin 1:
Openings in Foundation Walls and Walls of Enclosures (TB-1)
Provides guidance on the National Flood Insurance Program (NFIP) regulations concerning the requirement for openings in below Base Flood Elevation (BFE) foundation walls and walls of enclosures for buildings located in Flood Zones A, AE, A1-A30, AR, AO, and AH.
If enclosure walls are not designed with openings to relieve the pressure of standing or slow-moving water against them (called hydrostatic loads), the walls can be damaged or fail during a flood. If the walls are “load-bearing” walls that support the elevated building, failure of the walls may result in damage to, or collapse of, the building.
To address this concern, the NFIP (National Flood Insurance Program) regulations require that enclosure walls contain openings that will allow for the automatic entry and exit of flood waters.
These openings allow flood waters to reach equal levels on both sides of the walls, thereby lessening the potential for damage caused by a difference in hydrostatic loads on opposite sides of the walls.
In A zones, the requirement for flood openings applies to all enclosed areas below new elevated buildings and below substantially improved buildings.

Download the FEMA Technical Bulletin 1

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