Construction Industry Trends
May 2006
Tornados Touch off Building Code Debate
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While residents and businesses along the U.S. coast worry about preparing themselves for hurricanes, people in other parts of the country have another concern: tornados. Although they tend to garner less press then hurricanes, tornados can touch down anywhere, at anytime, and can cause significant damage and even deaths. Most often, though, they are found in the Midwest, in a region often referred to as Tornado Alley. Here, tornados are a fact of life—but according to the Institute for Building & Home Safety (IBHS), very few people are adequately prepared for them.
When asked if most buildings in Tornado Alley are built to withstand tornados, IBHS Vice President of Engineering Tim Reinhold has a simple answer: “Nope.”
The reasons, he says, often come down to money—and the law of probabilities. Since the chances of a tornado hitting any one building are very small—Reinhold estimates the return period as somewhere between 5,000 and 10,000 years—it doesn’t necessarily make economic sense to build a building that could withstand F4 or F5 tornados, which only account for approximately 1 percent of all the tornados that touch down in the United States. And with wind speeds ranging from 207 to 318 miles per hour, only a bunker would have a chance of surviving the impact of a direct hit from a tornado of this magnitude.
However, Reinhold believes that people in tornado-prone areas could learn much from the building habits of those in areas affected by hurricanes. “What we tell people is that if you were to build a house in the middle of the country the way you would build it on the coast for a hurricane, your house would likely survive 85 to 95 percent of the tornados that might occur,” he says.
One step that people can take to protect buildings against tornados is to increase the strength of the fastenings used to tie their homes together. “One of the facts that has come out of our research is that when you build a house the way we normally build it in the middle of the country, you’re only using about 10 percent of the strength of the materials that are actually being put into the house,” says Reinhold. “That’s because the connections are just kind of nailed together, rather than tied together with the metal strapping you see in houses built along the coast. But if you do take the extra steps to strap things together, then you use more of the capacity of what you’ve already paid for.”
Even though incorporating metal strapping into new buildings can raise construction costs 2 to 5 percent, the recent spate of publicity over deadly tornados may cause residents of Tornado Alley to rethink their construction practices. Currently, most buildings in the Midwest are only required to be built to withstand wind speeds of 90 miles per hour, meaning that even weak tornados can cause significant damage to them. In addition, newer building systems, such as insulating concrete forms, may make it easier for people to benefit from stronger built homes without having to spend a lot more money for them.
And even though the probability of a tornado hitting a building remains small, Reinhold believes building stronger makes sense for a number of reasons. “I think there are some benefits from building better that go beyond tornado protection. Your home is your biggest investment, and to tie it together well means that it’s going to stand up better in the long run. But people have to choose that that’s how they want to spend their money.”
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