By David Stauth, 541-737-0787
SOURCE: Rakesh Gupta, 541-737-4223
CORVALLIS, Ore. - The safety of homes and small businesses from hurricane-force winds sometimes comes down to the weakest link, researchers are finding, and even a few missing nails, bolts or straps can mean the difference between an intact structure and one destroyed by wind.
There may be a need for better training, more rigid inspections and simply more attention to detail in wood-frame construction in any region susceptible to high winds, scientists say, which includes not only hurricane regions but other large areas of the country prone to tornadoes or other large storms.
A Woodframe Damage Assessment Team supported by the National Science Foundation recently toured the areas devastated by Hurricane Katrina, and frequently found that the high winds would attack the most vulnerable part of a building and systematically destroy it from that point. "The most common weak link we found were gable end walls and eaves, where winds were at their greatest force," said Rakesh Gupta, an associate professor of wood science and engineering in the Oregon State University College of Forestry, and one member of the research team. "Often the connections failed where just a few nails or screws were missing, or some metal tie-down straps were not applied correctly."
Gupta, who is a national expert in wood frame construction techniques, and other members of the study team looked at about 30 residential and light commercial wood structures in Biloxi, Gulfport, and Waveland, Miss., and surrounding areas. They studied areas a little inland from the coast where the primary damage was from wind rather than the devastating storm surge of water from the Gulf of Mexico.
"We saw pretty clear demonstrations of what worked and what didn't," Gupta said. "In one case, for instance, some posts were supporting a porch roof. One post that was properly nailed at its base with four nails held up fine. But another with no nails at the base allowed wind to uplift the porch, collapse it and then cause major damage to the house."
A great deal of the inland destruction caused by the storm came from water damage, the scientists found, in which a window, gable end, vent, eave or other small portion of the roof or sidewalls would get ripped loose, allowing even more structural failure and then major water damage within the home. Most of those events could have been prevented by more meticulous attention to nailing schedules and proper application of hurricane straps, Gupta said.
At least some of the problem, Gupta said, may be that most carpenters and building contractors are not required to have any special training to do their trade.
"Our codes usually require extensive training and licensing for plumbing, electrical wiring, things like that," Gupta said. "About the only thing that often is not regulated is the actual building of the house. We might be able to prevent a lot of damage here if we required even a week or two of training in that area."
It may also be necessary, the researchers said, for building inspectors to be more specifically trained in the methods needed to resist storm damage, and more strictly enforce those practices in their routine building inspections.
The findings of research like this, he said, may also lead to minor adjustments in building codes that could improve the chances for storm resistance. A more frequent nailing schedule about every three inches might be useful in areas such as the eves of the roofs where wind forces are often at their most severe levels.
Other members of the NSF inspection team included scientists from the University of Alabama, Colorado State University, and two representatives of private industry.
Findings from the group's final report will be used to help develop better standards for wood frame construction, which includes most homes in the U.S. and many of its smaller commercial buildings.
The issue of building construction techniques, Gupta said, is not unique to areas prone to hurricanes.
"Most people in the United States live in coastal or inland areas that can be subject to intense stress from hurricanes, winter storms, tornadoes, or other very high winds," Gupta said. "This issue is national. We need to make sure that buildings are constructed not only to protect lives, but also to protect against expensive loss and damage to the structure. And that might often be accomplished simply by the proper enforcement of existing codes, the use of adequate nailing, bolts and metal connectors where required."
About the Department of Wood Science and Engineering: The Department of Wood Science and Engineering in the OSU College of Forestry has been ranked by the USDA as one of the top four such programs in North America. It uses science, technology, engineering and business practices to help society meet its needs for wood products and keep U.S. companies competitive in a global marketplace.