Flood Vents: Non-engineered openings are openings that are used to satisfy the prescriptive requirement that calls for 1 square inch of net open area for each square foot of enclosed area. A wide variety of options is available to satisfy the prescriptive requirements. The term “net open area” refers to the permanently open area of a non-engineered opening. The NFIP regulations indicate that flood openings may be equipped with coverings or devices provided that they permit the automatic entry and exit of floodwaters. The measurement of the net open area must take into consideration any coverings that have solid obstructions, such as grilles, fixed louvers, or faceplates. Manufacturers of devices intended for use as standard air vents typically indicate the number of square inches that each device provides for air flow (either stamped into the metal frame or noted on the packaging). The same number should be used for the net open area calculation when these devices are installed as non-engineered openings. However, in order to qualify as flood openings that permit automatic entry and exit of floodwaters, openings must not have solid covers that are installed during cold weather. Similarly, typical air vent devices that are designed to be opened and closed manually must be disabled permanently in the open position. Insect screens that do not impede the entry and exit of floodwaters are allowed and do not affect the determination of the net open area. For more information on Flood Vents: Non-Engineered see FEMA's Technical Bulletin-1 / 2008
