Still, underground shelters have their own set of problems, including the possibility that groundwater can seep in or that they can easily become moldy as condensation forms on their walls. They're also extremely expensive and notoriously unstable?and expansive soils in the southern U.S. can wreak havoc with them.
Instead, existing homes can be fortified with sheet metal, plywood, and heavy-duty hardware, and you don't even have to go to an architect or an engineer for plans. FEMA has some surprisingly straightforward plans (PDF) that an experienced amateur builder should be able to use to make a safe room in his or her house or basement. And it doesn't require exotic hardware to make high-strength connections to bolster a residential frame building. Chances are you can find most of what you need at a local home center or lumberyard.
One of the best names in the business, Simpson Strong-Tie, makes connectors that create a continuous load path, tying the house together from roof to foundation. Simpson has teamed up with university engineers to make the design and installation process as straightforward as possible. If you can read construction drawings and are familiar with using basic power tools, especially a rotary hammer or a hammer drill, it's likely that you can install the necessary connectors. These connectors give protection for F0, F1, and F2 tornadoes, which account for 95 percent of tornado activity. (For protection against an F1 tornado, Simpson Strong-Tie products cost $0.25 per square foot during new home construction. F2 protection costs $0.50 per square foot.)
Once winds start clocking in at around 165 mph, speeds equivalent to an F3, things get a little tricky. "By the time you get to that point, you're having problems with windows and roofs resisting those winds," says Randy Shackelford, vice president of the Simpson Strong-Tie Company.
Finally, if you decide not to harden your home, there are prefabricated solutions that use reinforced precast concrete. Mike Vaughn, president of the National Storm Shelter Association (NSSA) and Vaughn Concrete Products, says all NSSA-approved producers manufacture above-and below-ground shelters that can withstand 250-mph wind speeds, says. You can place these F5-resistant structures in your garage. Examples include the Model BP 3060 Storm Shelter from Central Alabama Storm Shelters, a six-person structure that costs $5500 plus delivery. Other structures can be installed in your backyard, such as this building from Safe Sheds, Inc., which costs $4785 for an 8 x 10?foot unit.
Ernst Kiesling, executive director of the NSSA and professor emeritus of wind engineering at Texas Tech University, says there are different advantages to above- and below-ground structures. "After the Moore tornado, I heard the media say that the safest place is being underground. That is absolutely incorrect," Kiesling says. Underground structures will face significantly less wind force but can be difficult to access, especially for the elderly or physically disabled. Kiesling says that it's best to make a house function more efficiently, such as reinforcing small rooms and designing with load paths. However, it can be difficult to retrofit entire homes once they are built. Storm proofing is best reserved for new homes or major remodeling.
Look for a storm shed or safe room that meets specifications established by the NSSA.
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