Floodplain Management

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Flood Openings and Compliance

By Bill Jones, CFM

From May 2014 Floodplain Management Today

The FEMA Elevation Certificate includes Section A. Certain structures are designed to have flood openings in accordance with local floodplain management ordinances. Section A is where surveyors provide information on openings that allow floodwater to enter a building to equalize the pressure against crawlspace and attached garage walls to prevent collapse in areas located below the Base Flood Elevation (BFE).

FEMA requires at least one opening on more than one wall. The requirement is that the openings provide a net surface area of at least one square inch for every square foot of enclosed area that is being vented. All areas subject to flooding must be vented and included in the calculation. Vents must be located within 12 inches of grade (inside or outside) and only the area below the Base Flood Elevation (BFE) can be calculated for compliance.

To illustrate the importance of using net area, in the example to the right, the gross opening area is 108.6 square inches, however, with 13 openings of 6.5” by 0.5”, the NET opening area is only 42.5 square inches.

Surveyors using the FEMA Elevation Certificate provide the net area, and if that area in square inches does not equal or exceed the enclosed area in square feet, floodplain administrators and insurance agents must use the “lowest floor, including basement or crawlspace,” as the reference floor for insurance and compliance.

diagram of where the openings should be

That would mean that the reference level for compliance and insurance rating would remain at the lowest floor; this is typically the bottom of the crawlspace or other area intended to have flood vents. Ornamental covers are allowed, however, as illustrated above, it important that the owner/builder understand the ramifications of partially covering these openings. Covers on openings must function without human intervention. If using covers with closures, they must be left in the open position.

Elevation Certificate sections A. 8. d) and A. 9. d) are available for engineered openings. If a Nebraska professional engineer provides demonstration and certification that an opening area lesser than the basic requirement, (1 square in of opening for each square foot of enclosed area) meets flood protection standards, the reference level may then be raised to the next higher floor. Documentation with the engineer’s seal and signature would be required to be attached to the elevation certificate. If you would like additional information on flood venting, see the list of technical bulletins on NDNR’s desk reference, where you can find Technical Bulletin 1 (Openings in Foundation Walls and Walls of Enclosures).

There are two companies that FEMA has approved for use of their “engineered openings,” Smart Vent, Inc. and Flood Flaps, LLC, they have provided documentation to FEMA to allow certification for a lesser ratio than 1 to 1 for the openings requirement. Flood Flaps certifies 220 feet of enclosed area per unit. Smart Vent certifies 200 square feet of enclosure for each 8”X16” unit. Additional information on these two is available at www.Floodflaps.com and www.smartvent.com. Please note that there may be other approved companies.

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