Building codes ignore tornadoes

Watching tornadoes turn houses and stores into piles of rubble in the Southeast and Missouri, you might think buildings would be required to meet some sort of building code designed to withstand deadly twisters.

But there aren't any tornado building codes, not even in Tornado Alley.

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.

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.

The city inspects for these standards, and builders adhere to them, he said.

Wess Galyon, president and CEO of the Wichita Area Builders Association, said that after the 1999 Haysville tornado, builders and code officials worked together to improve the way perimeter walls are tied together, and on ways to protect roofs from uplift.

The use of Insulated Concrete Forming systems, which can protect a major portion of homes against 200 mile an hour winds, also has grown over the years, he said.

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.

One group has tried to do something about a code for tornadoes. The American Architectural Manufacturers Association of Schaumburg, Ill., recently released a voluntary specification for testing and rating windows, skylights, and doors of buildings that might be exposed to tornadoes. It provides a system for rating their ability to withstand impacts and water penetration associated with tornadoes.

It offers different levels of protections for different buildings, such as hospitals, emergency rooms, shelters and police and fire headquarters.

The specification, pushed by an AAMA member from St. Louis, fills a void, said Ken Brenden, technical services manager for the association.

"In the past, architects were looking toward hurricane standards to fill that void and it didn't work because they are different events."

Although the new system is aimed at the commercial sector, he said, it could be adopted to residential dwellings and ultimately find its way into municipal codes.

"We would love nothing more than to see this adopted by local code jurisdictions," he said.

A tornado with winds of 110 to 120 mph can destroy a typical house in four seconds, his institute says. Flying debris is the first problem: it can shatter windows and doors and punch holes in exterior walls. Once an opening is created, air rushes inside and pressurizes the structure like a balloon being inflated.

The internal pressure builds and puts pressure on ceilings and the roof, which also is getting uplift pressure from the external wind.

Once the roof blows off, the walls can collapse.

There are steps homeowners can take to protect their dwellings against smaller tornadoes, Reinhold said. While the big storms get all the attention, his institute says that 77 percent of tornadoes have wind speeds of less than 110 mph.

"We advocate people spend a little extra tying their house together — connecting roof to wall and wall to foundation," Reinhold said. "You can do a tremendous amount to strengthen a house.

"It might cost 2 to 3 percent more to build that house, but then you're at a point where it's designed for 110 to 120 mph winds," Reinhold said.

Researchers supported by the National Science Foundation found much of the tornado damage in the South in April was due to inadequate connections between building members, especially trusses, roof rafters and walls.

But they also found that even the newest, safest buildings were destroyed by an EF-5 tornado, which has wind speeds in excess of 200 mph.

Storm shelters and safe rooms offer protection against those storms — if people use them, Reinhold said.

"There was a community around Birmingham where the builder had put tornado shelters in all the houses, and when the big tornado went through there, there were warnings, but nobody perceived them as a threat," he said. "In two cases out of 100-some homes, people actually went into the shelter."

This story was originally published June 5, 2011 at 12:00 AM with the headline "Building codes ignore tornadoes."