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What is The Difference Between Engineered and Non-Engineered Flood Opening?

Updated: Jun 25, 2019

Engineered Flood Openings:


Engineered flood openings are designed and certified by a registered design professional as meeting required regulations, performance standards, and design guidelines. Engineered openings have been designed and tested as flood vents and are given a flood coverage rating based on performance.


Compliant flood openings are required in all enclosed areas below the Base Flood Elevation in Special Flood Hazard Area Zones starting with A and V. For every 1 sq. ft. of enclosed area, 1 sq. in. of net free area is required if Non-Engineered Openings are used. If Engineered Openings are used, 1 sq. in. is converted to 1 sq. ft. Note that square footage of an enclosed area is measured from the outside of the walls. Each enclosed area is required to have a minimum of two flood openings on different walls.


The bottom of each opening shall not be more than 1 foot above the highest of the final interior grade or finished exterior grade immediately under each opening. Flood Openings are to provide passive hydrostatic relief to walls; human intervention is not acceptable to activate a flood opening. Therefore, any air ventilation devices that can be closed manually must be permanently disabled in the open position. Covers are not acceptable at any time over a Non-Engineered opening. If the Non-Engineered opening device has not been disabled in the open position or has a cover over the opening the result will be a “0” flood coverage rating for that opening. Standard foundation air ventilation devices that are designed to open and close based on temperature, Windows, and Entry & Garage Doors are not acceptable flood openings. See page 19 of FEMA Technical Bulletin 1-08 for a list of Unacceptable Measures.


Flood Openings must be below the BFE for them to perform their intended function. If any portion of the opening is above the BFE that area shall be deducted from the flood venting coverage the opening provides.


Non-Eningeered Flood Openings:


Debris is a fact of flood and because of rodent screens and other grills, Non-Engineered Openings have a tendency to clog. Clogged openings can lead to a build up of hydrostatic pressure causing walls to fail. When possible, professionals recommend to use ICC-ES Certified engineered flood openings to ensure performance.


Any louvers, blades screens, and faceplates or other covers and devices should be selected or specified so as to minimize the likelihood of blockage by small debris and sediment. Where experience has shown that a particular device or type of device has been blocked or clogged by flood debris or sediment, use of such devices should be avoided.


Clogged Air Vent Image from FEMA Technical Bulletin 1

“Non-Engineered Openings: Communities that administer the International Building Code® (IBC®) or the International Residential Code® (IRC®)should note the requirement to cover ventilation openings to keep animals and insects from entering. These codes provide a list of acceptable covering materials. The commentaries that accompany those codes note that some covering materials may reduce the gross open area of the vent by as much as 50 percent. In areas where floodwaters are expected to carry debris such determine that additional openings are required to increase the likelihood that openings will perform as expected, even if some become clogged with debris.” TB-1 pg.20


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