This spring has been one of the worst in recent history for deathly tornadoes, according to the National Weather Service. By the end of May, twisters had killed a reported 110 people across the country, well above the annual average of 62 deaths. Even worse, tornado season is far from over.
Such storms are also frighteningly destructive for buildings. That’s why reasonable precautions make sense for builders who operate in tornado country. After twisters tore through Oklahoma City on May 3, 1999, killing 36 people, destroying more than 10,500 structures, and doing a billion-plus-dollars’ worth of damage, Ideal Homes of Norman, Ok., (www.ideal-homes.com) decided to toughen up its houses with extra wind-resistant details. Thirty of Ideal’s recently built houses were among the structures leveled in the 1999 storms, remembers Ideal co-president for construction Todd Booze.
Of course, no wood-frame house can stand up to a direct hit from an F5-strength tornado packing 200 mph winds, Booze observes. But scientists say well-built structures have decent odds of surviving weaker tornadoes or near-misses by strong ones. So Ideal beefed up its homes’ construction by adding steel connectors between roof framing and wall framing, using J-bolts to anchor walls to slabs, and working with University of Oklahoma engineers to develop site-built shear-wall panels to add racking strength to wood-frame walls.
“We’ve come up with construction details that can flexibly provide reinforcement for different wall heights and window openings, supporting different roof pitches,” says Booze, who explains the assembly is similar to a box header. “Double studs, double top and bottom plates, connected to the foundation with anchor bolts and tie-down straps, and horizontal blocking through all of that, and then with OSB over it — sometimes on both sides of the wall, depending on what you need for the wall size and size of openings.”
Buyers seem to appreciate the sense of quality associated with the stronger construction, says Booze, but the features are not necessarily a big selling point. Given the hit-or-miss nature of tornados, customers don’t tend to want to spend big money on storm-resistant technology, even in Tornado Alley, the builder says. For example, Ideal Homes offers in-ground and above-ground tornado shelters as an option, but “generally, people don’t buy it,” Booze says. “They just don’t choose to spend their money that way.”
South of Oklahoma is Lubbock, Texas, which is another town with a history of tragic tornadoes. On May 11, 1970, a tornado killed 28 people in Lubbock while destroying hundreds of homes and damaging thousands more houses. The experience prompted Texas Tech University to found a major wind research facility on its Lubbock campus.
Now, after working with Texas Tech engineers, the city of Lubbock is supporting a program that replaces substandard housing with concrete homes built using insulated concrete forms (ICFs). Backed by a federal community development block grant, Lubbock has built more than 100 ICF houses, which provide high levels of safety and energy efficiency. (The effort has also helped the city develop a large and experienced ICF contractor base). How safe are these homes? According to Brad Reed, the program’s administrator, these structures built using this program are expected to survive a tornado strike 99 percent of the time.
For more information on Lubbock’s program, visit http://www.pathnet.org/sp.asp?id=20108.
Ted Cushman is a contributing editor to BUILDER magazine.