Storm Cellar - Typical Storm Shelter

Typical Storm Shelter

A typical storm cellar for a single family would be built close enough to the home to allow quick access in an emergency, but not so close that the house could fall on the door during a storm, trapping the occupants inside. This is also why the main door on most storm cellars is mounted at an angle rather than flush with the ground; an angled door allows for debris to blow up and over the door without blocking it and also decreases the force necessary to open the door if rubble has piled up on top. It might have a floor area of eight by twelve feet (2.5 × 3.5 m) and an arched roof like that of a Quonset hut—but it would be entirely underground. In most cases the entire structure would be built of blocks faced with cement and rebar through the bricks for protection from the storm. Doing this makes it almost impossible for the bricks to fall apart. New ones sometimes are made of septic tanks that have been modified with a steel door and vents. Most storm cellars would be reached by a covered stairwell, and at the opposite end of the structure there would be conduits for air that would reach the surface, and perhaps a small window to serve as an emergency exit and also to provide some light. Storm cellars, when connected to the house, may potentially compromise security.

Fully enclosed underground storm shelters offer superior tornado protection to a traditional basement or cellar because they provide overhead cover without the risk of being trapped or killed by collapsing rubble from above. For this reason they also provide the only reliable form of shelter against "violent" (EF4 and EF5) tornadoes which tend to blow the house off the foundation, removing the overhead cover protecting the occupant.

There are several different styles of storm cellars. There are the typical under-ground storm/tornado cellar, also called storm or tornado shelters as well as the new above ground safe rooms. A "cellar" is an under-ground unit, but for the sake of the specified use of a "storm cellar," to protect one from high wind storms, it seems relevant to mention safe rooms. There are 2 basic styles of "under-ground storm cellars." One is the "hillside" or "embankment," the other is the "flat" ground.

Hillside or embankment models are usually installed in one of two ways. It can be installed in an existing hill/embankment or dirt is built up around a free standing unit forming a hill around it. The door can be set at an angle or vertically. There can be steps leading into the unit or it can be installed to where the floor is level with the ground outside. As with all storm cellars or storm shelters, they are usually manufactured from concrete, steel, fiberglass, different injection mold type plastics, and any number of composite materials on the market today. Each one is made and installed differently, but the basic idea is the same. The embankment storm cellar can be made from concrete, steel, fiberglass, or any other structurally sound material or composite and is usually installed in a hill or embankment leaving only the door exposed. These can usually be built to your specific need. In some cases they can hold an entire neighborhood or town as with a community shelter. More often though, they are built to hold one of two families, specified as a residential shelter. The fiberglass cellar is made from fiberglass. If any shelter is designed and built according to certain guidelines then it can be called a tornado shelter which will provide near absolute protection. All under-ground "storm or tornado" shelters must be properly anchored. Due to hydro-static pressures, and more simply put ground water, necessary calculations must be made to ensure the shelter will not float out of the ground over time. The underground polyethylene shelter uses a unique tapering design in which, installed by factory specifications, will be held underground by the surrounding soil. This type of unit also has a unique wall design. It uses a hollow double wall that fill up with water which assists in weighing the unit down, keeping it from floating out. However, the double wall design will bow-in under excessive water pressure. If the water table is high at any time during the year you might consider sticking with a single wall design. The flat ground cellars are designed so that the door is flat with the ground and can be made from any one of the material previously described. This unit is put in a hole deep enough to cover the bottom section, and then the excavated dirt is filled in around the top and packed down. Storm shelters must be designed, built, tested, and installed properly for them to meet any of the FEMA-320 2008 "Taking Shelter from the Storm" 3rd Edition, FEMA-361, ICC-500 Standard, NPCTS (National Performance Criteria for Tornado Shelters), and ICC/NSSA Standard. Adequate testing can be found in the ASTM E 1886-05 "Standard Test Method For Protective Systems by Missiles." Design, construction, testing, and installation should be overseen and/or review by a registered professional engineer. Always ask for the Stamped Engineer Drawings before purchasing a unit.

There is little to no policing of the storm cellar production or installation by any government agency or association. For example, the Federal Emergency Management Agency and the National Storm Shelter Association do not police the manufacturer or installation of any storm, hurricane, or tornado cellars. Some associations inspect 1 shelter for every 100 built. Many professional engineers do not actually inspect storm cellars. They are only responsible for making sure that everything in the "drawing" is correct. It is up to the manufacturers to produce a safe unit, built according to the drawings submitted to a registered engineer. Installers must follow the factory provided instructions for installation. It is up to the consumer to inspect the product they are purchasing!