A significant part of damage caused by flood is the pressure difference between water inside and outside a structure. This can happen both when the flood is rising and when it is ebbing. Flood vents are devices to allow water to flow freely between the inside and outside of a building's foundation, equalizing the pressure. The Federal Emergency Management Agency (FEMA) and their National Flood Insurance Program (NFIP) have set minimum vent requirements for structures in a flood plain.
Number of Vents
The FEMA requirements are for 1 square inch of flood vent opening for every square foot of floor space. Un-engineered flood vents are required to literally adhere to this 1 for 1 requirement. Engineered flood vents allow more water to flow through and are more efficient at balancing the pressure on each side of the foundation, therefore the number of square inches required for a given area is adjusted downward. In addition to area requirements, there must also be at least two vents for every enclosed space in the foundation.
The vents must be installed less than 1 foot above either the interior or exterior ground level, whichever is higher. They must be placed so that water can flow freely without impediment in and out of the foundation's enclosure, and as close to corners as practical. Grills and screens installed to prevent entry by animal pests must be corrosion resistant and must not interfere with the free flow of water into and out of the foundation's enclosure.
Structures that Require Vents
The regulation states that structures below the base flood elevation (BFE) such as basements, crawl spaces, garages are required to have flood vents. FEMA defines the BFE to be the elevation that floodwater is expected to reach during the base flood. The base flood is a flood that has a 1 percent chance of being equaled or exceeded during a given year.
Besides reducing the likelihood of serious foundation damage during a flood, having properly installed flood vents will greatly reduce your insurance premiums. The first is a savings you hope you will never realize, but the second is certain and will repay the cost of the vents fairly quickly.
- Photo Credit flooded buildings in york image by Mike Shannon from Fotolia.com flood image by dinostock from Fotolia.com
Crawl Space Ventilation Requirements
Building codes vary from region to region, but there are some basic requirements when considering ventilation for a crawl space. The primary...
Flood Plain Building Restrictions
To participate in the National Flood Insurance Program (NFIP), a community must agree to take on the responsibility of floodplain management. One...
What Size Vent Do You Install for a Toilet Drain?
The sinks, toilets, showers and bathtubs within your home are all connected to a plumbing and venting system. An air vent is...
How Much Venting Is Needed for a Crawl Space?
Proper venting of a construction crawl space provides a continuous flow of outside air throughout the area. Crawl space ventilation standards, however,...
How to Install a Foundation Vent
Ventilating the crawl space under a structure's foundation prevents mildew and rot from attacking the subfloor. Water vapor in the soil escapes...
- FEMA's Building Requirements in Floodplains