The Wichita Eagle on Sunday reports that many building codes adopted by cities and counties ignore standards for tornadoes.
The International Building Code adopted by many cities, including Wichita, address natural disasters such as earthquakes, hurricanes and floods, but not tornadoes.
Experts say it would be impractical and costly to require structures that could withstand the killer EF-4s and EF-5s that have seemed to dominate the recent storm season, although there are ways to lessen damage from smaller storms.
Local governments sometimes modify the building codes the adopt by simply including the amendments in the incorporating ordinance. The City of Wichita has done this to a certain extent to accommodate for strong winds:
Wichita’s code has an amendment requiring structures to be designed for 90 mph straight-line winds, said Kurt Schroeder, superintendent of central inspection. The code also includes an amendment requiring any storm shelters that are built, or structures that are designated as storm shelters, be designed in accordance with Federal Emergency Management Agency standards.
FEMA guidelines govern resistance to wind loads and windborne debris impacts. They require safe rooms to withstand winds up to 250 mph, protecting against the impact of a 15-pound two-by-four flying at 100 mph.
The city doesn’t mandate such shelters, except in mobile home parks.
“Those would be pretty much concrete, hulking structures and no openings, except for heavy-duty doors,” Schroeder said.
In-home shelters are more practical, if costly. FEMA estimates the costs of constructing a safe room inside a new home or small business can range from $6,500 to $8,500 for an 8-foot-by-8-foot room. Larger, 14-foot-by-14-foot rooms can cost from $11,500 to $13,500.
Schroeder said basic wind speed standards in the city code relate to issues such as uplift on roof structures, straps on corners of framing, minimum distances from corners for windows, and nailing patterns.
Building codes don’t contain standards for tornado impacts because it doesn’t make economic sense:
Codes for tornadoes don’t exist because the likelihood of two twisters striking the same place are extremely rare, said Tim Reinhold, senior vice president for research and chief engineer at the Institute for Business and Home Safety in Tampa, Fla.
Reinhold said the chances that a tornado will hit a particular building twice is between one in 5,000 years and one in 10,000 years.
So forcing homeowners to build tornado-proof structures doesn’t make economic sense.
“There’s such a low probability that nobody is doing that except nuclear power plants and data centers,” he said.