Why aren't homes built to withstand tornadoes?
The slight probability of an individual house being hit by a devastating twister is too small to make it worth the cost. That's not the case for earthquakes and hurricanes.
Looking at homes reduced to collections of rubble by the recent string of tornadoes raises a question: Why aren't homes built to withstand tornadoes?
The answer, surprisingly, is probability. And cost, of course.
The chance of a devastating tornado hitting any one home is so small that it's not considered economically efficient to require all homes in the tornado belt to be built to withstand a twister. The chance of any one home being affected by an earthquake or hurricane is significantly greater, which explains why building standards are higher in earthquake- and hurricane-prone areas.
"In some areas of California, earthquakes happen tens or hundreds of years apart, and they affect a tremendous area with a lot of properties," Tim Reinhold, senior vice president for research and chief engineer at the Institute for Business and Home Safety, told Life's Little Mysteries. "But for a tornado hitting a particular location in Tornado Alley, you're dealing with return periods of thousands of years."
Most homes in the United States are built to withstand 90-mph, though Florida and North Carolina require stricter standards for hurricane resistance.
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Even those standards are not strong enough to withstand the strongest tornado, which can bring 250-mph winds.
For a home to be "tornado-proof," according to a wind research center online report, the walls, roof, windows, doors and garage doors would have to be "missile-resistant" to halt penetration by flying debris, and the connections of the structural elements would need to be capable of withstanding 250 mph wind pressures.
Additionally, the connections for long-span roofs and tall walls to transfer the loads induced by a 250 mph wind would have to be 7½ times stronger than those routinely required by today’s codes, the wind research center reports.
"Realistically speaking, it is not practical, much less reasonable, to build a tornado-proof house," the report notes.
There are things you can do to protect your home from a lesser tornado, including many of the measures required in Florida and other coastal states for wind resistance: stronger garage doors, impact-resistant windows and stronger roof fastenings, for example. If you're building new or doing a major remodeling job, some of these features can be added for a small cost.
Texas Tech has information on lots of resources, and the Institute for Business and Home Safety also has information on measures you can take to strengthen your home against tornadoes, earthquake and hurricanes.