Types of Storm Shelters

Storm Forces

• Three damaging forces are considered in the design of a storm shelter. The first are wind pressure forces. In a tornado, wind forces may exert 200 pounds per square foot on the walls of a structure. Second are the air pressure forces that occur when a zone of extremely low air pressure such as the vortex of a tornado passes nearby. The third damaging force is the penetrating impact of debris carried by the storm. This may include pieces of other houses, utility poles and trees.

Inground Shelters

• Underground storm shelters are the most popular in many parts of the United States. They are often constructed of reinforced concrete and have a thick, soil-covered roof to counteract uplifting wind forces. A proper venting system serves to equalize low air pressure forces. Heavy metal doors, counterbalanced for easy opening, shield against wind-borne debris. Since most inground shelters are installed some distance away from the house, proximity and quick access may be an issue. Also, soil conditions such as a high water table make in-ground shelters unfeasible in some areas.

Aboveground Shelters

• Located inside the residence, aboveground shelters have the advantage of being planned for and built into a new house, or easily added as an addition to an existing house. However, they also carry the engineering challenges of creating a safe room that can withstand the storm forces and offer the level of protection available in an underground shelter. Walls must be made of cast concrete or cinder blocks with their cores filled with cement. Walls and ceiling must be reinforced both laterally and vertically. A 2-inch thick wood door, reinforced with steel, should be located on the interior side of the shelter leading to the house. Because house fires are a potential after-effect of storm damage, consideration should be given to making the shelter fireproof, as well.

Construction Considerations

• Storm shelters should not be makeshift constructions. Build from a plan created by an engineer or architect. Many universities in storm-prone areas of the country can provide advice, including standard blueprints for inground and aboveground shelters. Once you get a plan designed by a professional, make sure your contractor follows it.