Construction Materials and Methods for Withstanding TornadoesThe Federal Emergence Management Agency (FEMA) and several universities are currently researching materials and construction designs that resist falling and flying debris and withstand winds caused by tornadoes.
The FEMA project at Clemson University has shown the use of metal-reinforced wall panels provides far greater safety against falling debris than wood stud and fiberboard sheeting construction. This could result in a "low-tech fix" for existing homes through the addition of a layer of metal decking under the wall panel. Other "fixes" such as different combinations of plywood or insulation foams are also being investigated.
Texas Tech University found that 6-inch insulating concrete walls shattered a 15-pound, 2x4 wood stud fired at over 100 miles a hour; while wood frame and steel frame walls, even covered with brick veneer, were penetrated by the stud.
FEMA surveys indicate that incomplete design and construction for load transfer and improper connections between roof tresses and wall systems cause most structural failures of buildings due to uplift wind forces. Metal fasteners, called hurricane clips, and straps which are adequately sized and properly installed on wood-frame structures help resist tornado's uplift winds.
Some insurance companies are recommending anchor bolts with heavy-gauge, square bolt washers be installed in existing homes or new construction to connect the floor construction to the foundation, thus reducing the chance the home will be lifted off its foundation. It is suggested that metal connectors be used to attach roof trusses or rafters to the walls. As long as plywood or OSB (oriented strand board) are properly nailed and installed, they can adequately connect the wall and floor components. High wind resistant roofing products should be installed with hot-dipped, galvanized nails.
Entry doors should be solid wood or hollow metal, installed with at least three hinges and a one-inch, dead bolt security lock. Single panel garage doors are more wind resistant than double door panels and should have horizontal bracing. Check with the manufacturer about retrofit bracing kits for existing doors. Windows should be of impact resistant, laminated material or covered with impact resistant shutters.