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March - April 2003

Hurricane-Sized Challenge
Window Manufacturers Strive to Meet Challenge of Impact-Resistant Glazing Codes
by Michael Fischer

Building codes requiring impact-resistant glazing are no longer confined to Florida; rather, they are moving up the East Coast of the United States. Thus, window manufacturers are stepping forward to assure their products meet the demands of these new codes. 

Manufacturers Develop New Products
Working with glass manufacturers, glass laminators and their own design staffs, window manufacturers have created products aimed specifically at the markets where impact resistance has become an issue. At the same time, manufacturers are creating tools to help their customers better understand the requirements of the stringent measures that were first adopted in Florida’s Dade and Broward Counties, but which are increasingly being seen in other jurisdictions as well.

“Dade and Broward Counties were the first to adopt impact-resistant language in their codes as it regards windows,” said Jim Krahn, manager of advance research for Marvin Windows and Doors in Warroad, Minn. Krahn, who is chairperson of the performance, testing and certification committee of the Window & Door Manufacturers Association, added, “The trend is moving up the East Coast and has now reached into parts of 16 states and a total of 138 counties. When it was confined just to those two Florida counties, and for that matter, the warm-weather states of the Southeast, it was less complicated. We were talking primarily about single glazing. But, as it goes further north, where insulating glazing (i.e. double glazing) is more predominant, it changes the whole picture.”

Krahn pointed out that if window manufacturers want to continue to market in areas where impact resistance is mandated by codes, they must develop products that meet the requirements. 

“In some cases, this might even mean redesigning the sash to accommodate greater glass thicknesses,” he said. 

The problem escalates where larger windows are concerned. 

“If you stick with smaller units, it is easier to pass the tests for impact resistance. The larger the glass area, the more difficult it becomes,” said Krahn. 

To meet the challenge, Krahn said a cooperative effort is needed among window manufacturers, glass producers and companies that make the film used in laminated glass. “We might find it necessary to create new products and processes,” he said.

Two Window Giants Get Involved
Some window manufacturers have already created products designed specifically to meet the demands of impact-resistant language in building codes. Two of the most active firms in this area are Andersen Corp. of Bayport, Minn., and Pella Corp. of Pella, Iowa. Both companies, among the largest producers of windows in the nation, have product lines available to meet the demands of the new marketing realities of impact-resistant glazing. Both have also taken steps to create their own testing protocols to assure their new products meet the standards even before they are exposed to the necessary step of certification by an independent testing laboratory.

Chris White, code compliance manager at Pella, said the company has made a substantial investment in its efforts to meet the realities imposed by impact-resistant glazing requirements. 

“We have done two things. First, we have a line of impact-resistant windows called Hurricane Shield, which we market in those areas where impact resistance is an issue,” said White. “Secondly, we have created our own in-house testing program to assure we meet the standards imposed. The fact is, products which meet the impact tests are, by nature, very expensive—much more so than our standard lines.”

White also suggested that the impact-resistance requirements limit the design options. “I know of no wood, double-hung windows that are able to meet the standards, although I suspect that other manufacturers may have some available in their product lines,” she said. “We have found that 
the requirements imposed by the codes are best met with casement windows, patio doors, awnings and a limited number of fixed windows.”

Andersen, too, has developed windows that meet the code requirements, according to Steve Berg, product manager of specialty windows. 

“We’ve adapted our existing product line to meet the requirements for impact-resistant glazing,” said Berg. “For windows with monolithic (single-pane) glazing, everything remains pretty much the same in terms of design and profile. The same is true for double glazing. We offer those windows with an impact-resistant glazing option.”

Andersen, like many of its competitors, has its own in-house testing lab, which now includes testing for impact resistance.

“We want to make sure our windows are going to meet the standards even before we send them to an independent test lab for certification,” Berg said.

He also pointed out that including impact-resistant glazing in Andersen windows increases the cost per unit. 

“There has to be a cost difference, because we are talking about a more expensive glass construction that meets a higher level of performance,” he said. 

Berg also revealed that Andersen has taken it upon itself to embark on an extensive educational program for its dealers and customers. 

“We think it’s incumbent upon us to take the mystery out of the impact-resistant codes,” he said.

To that end, the company has a code expert traveling to areas of the country where code changes are taking place to gather current information. Armed with that information, Andersen is developing training tools and creating seminars to educate dealers and builders concerning the code requirements in their areas.

Impact-Resistant Trend to Continue
All parties warn that the trend toward impact-resistant glazing requirements is just beginning. One firm in close touch with the situation is DuPont, which works closely with glass manufacturers in developing laminated glass products. Tom Kopec, North American architectural manager for DuPont, said his company has gone so far as to introduce a new lamination product called Sentry-Glas Plus®, a polyvinyl butyl material that it says is five times more rigid than previous materials. The material is designed to keep the glass from deflecting, thereby allowing it to meet the code requirements.

“There is little doubt that the trend toward impact-resistant glazing in codes will continue,” said Kopec. “Both the International Residential Code and the International Building Code now reference impact resistance, and there is every likelihood that code jurisdictions employing those codes will be closely considering whether that provision fits the wind conditions in their areas and whether they should include impact resistance in their requirements.”

Even in areas where hurricanes are not a factor, there is the likelihood that impact- resistant glazing could be mandated by local codes. 

As the technical performance requirements for windows have become more complicated, the glass industry has responded with more in-depth research and development. The ASTM Glass Strength Task Group released the 2002 version of ASTM E1300 recently, the industry standard for determining the load resistance of glass used in building products. This new version of the standard provides more comprehensive design data reflecting the most current information available to the ASTM task group. The new version includes more support conditions, more glass aspect ratios, deflection charts and more combinations of insulating glass configurations. This version is also based upon a 3-second load duration, which ties more directly to the American Society of Civil Engineers standards as well as the International Codes 3-second gust factor. The most important change to ASTM E1300, however, is the addition of a new series of charts for glass laminates. The addition of those charts is in keeping with research evaluating the strength of laminated glass configurations. 

The ASTM task group has responded to a need for more complete glass design data to assist the window industry in meeting the tricky demands of impact resistance and energy performance. The partnership between glass producers and window manufacturers has never been more important.
“In areas where tornadoes are prevalent, or in mountainous areas where high winds occur on a regular basis, there is every possibility that impact-resistant glazing may become an issue,” said Berg. “That’s why it behooves us, and all window makers, to take a proactive stance. We need to be ready with products that meet the needs of the marketplace.” 


Michael Fischer serves as director of codes and regulatory compliance for the Window and Door Manufacturers Association, based in Des Plaines, Ill. 

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