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Damage to this apartment building was caused by inadequate nailing of sheathing to trusses and of trusses to the top plate, according to the damage assessment team of the American Wood Council.
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By Dan McLeister
The lessons from Hurricane Katrina are broad reaching, affecting everything from emergency response systems, rescue protocols and infrastructure development to land-use concepts, construction techniques and building materials.
Building systems and practices have undergone especially close scrutiny by a host of investigative teams from the insurance, builder and building material industries.
As a result, a number of lessons for the building and remodeling industry are already becoming clear:
- Change the way we build—or, more correctly, build the way we are supposed to build by following approved construction techniques and details;
- Enforce the use of approved construction techniques by including them in the codes;
- Consider the use of new building systems and alternative materials.
Better building techniques
A disaster investigation team from the American Wood Council of the American Forest & Paper Association found numerous building construction practices in need of improvement. The team, for example, found some roof truss connection failures and many homes that had lost roof sheathing.
The problem: Nailing of sheathing to trusses was what the team called "minimal." In one observed case, there was only one nail per truss, rather than the multiple nails that are required under the 2003 International Residential Code. Each truss also appeared to be connected to a wall top plate with a single uplift clip using two or three 6d box nails, rather than the multiple nails required.
In some cases, when trusses did not separate from top plates, the entire assembly–including trusses and top plate–separated from the wall. In these cases, top plates were connected with nails driven into the end grain of studs, a configuration that has no assigned withdrawal capacity in the National Design Specification for Wood Construction.
The wood industry has compiled The Wood Frame Construction Manual for One- and Two-Family Dwellings, which contains approved design and construction techniques for coastal areas potentially affected by wind. The AF&PA has distributed copies of the manual to building departments in the areas hit by Hurricane Katrina.
Jon Luther, executive vice president of the Home Builders Association of Greater New Orleans, offers these additional hurricane-area building tips:
- Insist on enhanced window treatments such as the installation of windows with impact- or hurricane-resistant glazing or windows with hurricane clips already attached to the frame to allow for easy acceptance of window coverings;
- Install metal strapping all the way from the foundation to the rooftop;
- Make sure that sheathing–OSB or plywood–wraps the entire house.
Stronger codes
Another lesson is that strong codes result in strong buildings. There had been only a voluntary code in Louisiana. That state is now poised to rebuild stronger and safer homes using the International Codes (I-Codes) developed by the International Code Council, which will be required of all buildings built or rebuilt statewide starting in 2007.
Under the new Louisiana legislation passed in December, the 11 parishes hit hardest by Hurricane Katrina had 90 days to begin implementing and enforcing the wind and flood provisions of the International Building and Residential Codes. The code requires homes and businesses built along the Gulf Coast to withstand winds of 130 to 150 miles per hour. The bill also established a 19-member council to oversee enforcement of the codes by local governments.
Alternative materials
To meet the code requirement challenge, some builders are looking to alternative materials and building systems. Andrew Marshall of IM Construction, Baton Rouge, La., stopped building houses with wood even before Katrina. He turned to steel framing and plans to stay with that material.
"I didn't lose any of my customers' houses to Katrina. Some were in areas where the wind speed reached 140 miles per hour," said Andrew. "Of course we had to replace gypsum and insulation after the houses were dried and cleaned out. In wood houses I would be concerned about what might be growing in the wood framing after the house was dried out and cleaned up."
According to the Steel Framing Alliance, steel frame construction can help mitigate the instance and growth of mold in buildings. The alliance () provides guidance for builders and has an information sheet titled Mold: One More Reason To Build With Steel Framing.
For builders seeking other alternatives, the Portland Cement Association, in cooperation with several other concrete industry associations, will provide information in seminars in April 2006 about such systems as insulating concrete forms, precast concrete systems and concrete masonry construction. Concrete systems, according to the association, help buildings resist high winds, flying debris and storm surges.
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