An F5 tornado, with winds of 200 mph or higher, can obliterate virtually any wood-frame house. But following this week's tragic Oklahoma tornado, experts are advising that it might still be worth building houses better — because relatively small changes in construction methods can increase the odds that a house will stand up to weaker, smaller tornadoes, or will perform better in a near miss by a big tornado.
NBC News has that story here ("Tornado-proof homes? Up to 85 percent can be spared, expert says," by John Roach). Civil engineer Andrew Graettinger from the University of Alabama told NBC that "inexpensive construction techniques could have kept up to 85 percent of the area's damaged houses standing." Using metal connectors and straps to strengthen the connections in the uplift load path, better tying the house walls to the foundation and the roof, would help more houses survive, said Roach.
Even when homes are destroyed, a tornado safe room could save the lives of the residents. But according to a report in the New York Times, homeowners in Tornado Alley typically aren't willing to pay for the upgrade ("Why No Safe Room to Run To? Cost and Plains Culture," by John Schwartz).
Moore, Oklahoma, the site of this week's catastrophe, has been hit by a killer tornado before. But construction methods there have not changed much in the intervening years, the Times reports. "In a 2002 study published in the journal of the American Meteorological Society, Timothy P. Marshal, an engineer in Dallas, suggested that 'the quality of new home construction generally was no better than homes built prior to the tornado' in 1999," the paper reports. "Few homes built in the town after the storm were secured to their foundations with bolted plates, which greatly increase resistance to storms; instead, most were secured with the same kinds of nails and pins that failed in 1999. Just 6 of 40 new homes had closet-size safe rooms."