Many places are prone to natural disasters, such as hurricanes and tornadoes, that generate extremely high winds. In addition to heavy property damage, these winds may present grave dangers to home occupants and pets. The threat of these disasters has led to the development of storm shelters. In cases of emergency, quality shelters provide safe and quick escape from dangers posed by these storms.
However, when choosing to build a shelter or to buy a prefabricated one, homeowners should take care that their shelters' design and construction meet standards. Homeowners may choose from four types of shelters: underground, aboveground, berm, and prefabricated. Although these types of shelters may vary by design, many different issues inherent in building shelters require design by professionals.
Underground Storms Shelters
Underground shelters guarantee the most protection against strong winds, however they also have several drawbacks. First, they require extra considerations to build. For this type of shelter homeowners must dig deeper holes on their property, which adds to construction cost and time. Designs may also have to address underground piping or wires. They also may be impractical in areas with high water tables or high-level bedrock.
In addition, underground shelters may be more susceptible to ground pressure, especially with saturated soils, and a shelter's construction must withstand that pressure. Underground shelters should include an especially heavy roof to counteract uplifting forces from the storm. As discussed below in the Access Section, building shelters inside a home is preferable as access is quicker and building underground shelters in existing homes requires substantial modification.
For this reason, underground shelters are more practical when built in conjunction with homes. The shelter should thus be included in home construction plans and meet local codes.
Berm shelters are similar to underground shelters except that part of the structure remains exposed. Like underground shelters, they also require heavy ground excavation to build the shelter, however, they allow extra relief of the ground pressure if designs include drain lines connected to sumps or open discharges.
You should remember that a sumps rely on fans which are susceptible to power outages. Experts also recommend waterproofing the exterior walls so that interior walls remain dry.
Above Ground Storm Shelters
Although aboveground shelters do not provide as much protection against high winds and projectiles as the underground type, designs do not need to address the additional environmental factors of underground shelters. The shelter may consist of an attachment to a house or an interior room such as a large bathroom or walk-in closet.
Nevertheless, these shelters must feature solid construction. Their walls and roofs must be thick and continuous. If located outside, the shelter be securely anchored to the ground with piers that reach the span the entire height of the structure. An additional barrier wall may surround the shelter but must be connected to the roof.
If you live in the northern hemisphere, then you should locate the door on the the north or east side to minimize impacts from projectiles. Conversely, those located in the southern hemisphere should locate their doors on the south or west side of the shelter. If you shelter does not feature this barrier wall, then an heavy entrance door coated with plate steel may suffice.
You may also include a second interior door if you use your shelter for purposes besides emergencies. However, this door should open inward so that storm-tossed objects do not jam the door and prevent exit. Aboveground shelters located outside may also have aesthetic impacts and local codes may contain more requirements than those for underground shelters.
Prefabricated shelters offer several advantages. First, they are less expensive than shelters built on-site. Also, homeowners may erect them much more quickly than shelters built on-site, a consideration which may be important when storm seasons approach. Yet, they may not be suitable for all situations. Mass producing these shelters undermines their adaptability to different situations.
For example, an irregularly shaped lot may not accommodate the more regular design of a factory-built shelter. They may be built may be built indoors or outdoors. However, the outdoor variety requires more time to construct. Finally, a homeowner cannot supervise construction of a shelter. When buying prefabricated shelters you should take care that they carry certificates of authenticity and warranties.
General Design Requirements for a Storm Shelter
Since the purpose of building or buying a shelter is to shield occupants of a dwelling from dangerous storm conditions, protection against those elements represents the primary design consideration. Storms such as hurricanes and tornadoes primarily engender three dangers: strong winds, projectiles hurled by these winds, and pressure changes. Your shelter should conform to the industry standards set by the National Storm Shelters in the United States which maintains a list of members.
Hurricanes and tornadoes generate winds measuring hundreds of miles per hour and delivering 50 to 200 pounds of force per square foot, easily capable of destroying structures. They may also grab objects on the ground, such as lawn equipment, and hurl them through the air adding additional force to the wind. Therefore, storm shelters require solid construction with walls of reinforced concrete.
In addition, the reason that these storms generate high winds is that they are essentially centers of extremely low pressure. Differences between higher pressure inside structures and those of the storms, as high as two hundred pounds per square foot, may cause structures to burst outwards. Experts recommend a ratio of one hundredth the total cubic footage of a shelter for venting. Installing pipes with diameters equivalent to recommended ratios addresses this issue.
The design or choice of a shelter also depends on the number of people to occupy it. You should remember that some storms such as hurricanes may last several hours and occupants may need to sit. The United States Federal Emergency Management Agency recommends at least six feet of space per person. Experts recommend against using a shelter for other purposes such as storage or office. If you do intend to use your shelter for other purposes then you should increase its size, to at least ten feet per person. In these cases, installing shelves along a single wall also economizes space.
Electronic equipment, such as a television or radio may also be placed under the shelving. This space may also accommodate foldaway beds. In addition to basic supplies such as food, blankets, and first aid, you should also consider using this space for valuables and important documents.
Storm Shelter Access
Shelters located inside a home are preferable because they allow occupants direct and easy access. Having to cross a yard may cause injury and there may not be sufficient time to reach the shelter. Access to the shelter should also emphasize speed and ease with unlocked, counterbalanced doors and handrails for steps. Experts also recommend against locking shelters when storms approach in case keys are misplaced or otherwise unavailable.
Costs Involved with Storm Shelters
As shelter types and environmental considerations vary widely, so do shelter costs. However, a shelter may cost from $2,000 to $14,000 for the most durable, sturdiest variety.
Building a storm shelter may be advisable or necessary in many areas that experience frequent violent storms such as tornadoes or hurricanes. When deciding to build or buy a shelter you should consider take a number of factors including the environmental setting which may subsume constraints like high water tables, time to build, location and the number of occupants.
Although costs vary widely among shelters they potentially may save lives and therefore costs should not represent an overriding factor. If building a shelter you should also hire a professional to design and construct it to ensure the highest level of durability and security.