Hurricane and Tornado Glazing— Don’t Get Them Mixed Up

By Ellen Rogers and Drew Vass

If you’ve ever wondered what the difference is between tornado and hurricane glazing—or even why there are distinctions to begin with—think of it like this: “Tornado glazing is an impact product on steroids.”

That’s how Dean Ruark puts it. The vice president of engineering and product development at PGT Industries is not alone. Others in the protective glazing field agree that, though both are impact products, tornado glazing is in a class of its own. If you’re a door and window dealer or contractor who delves in commercial construction (some parts of which require tornado glazing these days), or that plans to offer impact-rated doors for residential safe rooms, it’s important to note
the differences—especially when it comes to certifications and ratings.

“A tornado is a different animal,” says Gerry Sagerman, who works in sales development for Insulgard Security Products, and therefore requires different levels of impact-resistance, he adds.

While hurricane glazing products are well-established in the marketplace, tornado products are still relatively new. For this reason, there remains some confusion and misunderstandings surrounding their uses, Sagerman suggests. Depending on the region, state or jurisdiction a home lies within, certain applications call for certain products. Meanwhile, the system for selection is code-driven, making it critical for the right products to be used in the right applications.

Hurricanes vs. Tornados

Understanding the differences in hurricane and tornado glazing begins with understanding the forces the products are designed to withstand. Hurricane-resistant glazing is meant to help protect the interior of a building from the high winds, strong rain and projectiles that form when a hurricane makes landfall. If a door or window is breached during a hurricane, wind and rain can penetrate the building and cause structural damage—including roof liftoff (the ultimate disaster). Given the warnings that come prior to a hurricane, most people have likely evacuated the area, compared to a tornado which provides little warning.

The 2015 International Building Code (IBC) references an updated International Code Council (ICC) 500 section, Standard for Design and Construction of Storm Shelters, which requires certain buildings in high-risk areas to incorporate tornado-safe rooms into their construction. For new schools, first-responder facilities, or select community centers in 250-mph wind zones, a safe room is required. Those facilities and all of their doors and windows must comply with the ICC 500-2014 standards.

“Safe room windows and doors are built specifically to protect people in the case of a tornado,” says Sagerman. “The test for tornado glazing is a 15-pound two-by-four shot at 100 mph, compared to hurricane glazing, which is a nine-pound two-by-four shot at 120 mph. That great amount of impact [in the tornado test] is 10 times the amount of load compared to Miami-Dade.”

Sagerman adds that though there are similarities in testing for tornado and hurricane glazing, there are also some key differences.

“They both require pressure test and then they both require an impact test, and then for hurricanes you have to cycle test due to considerations such as the flying debris,” he says. “You have to make sure the windows will stay in place during that storm, and that’s because a hurricane lasts much longer than a tornado.”

Ruark explains that the purpose of hurricane glazing products is to resist windborne debris.

“Dade County is the most stringent, and we’ve worked on these products designed around withstanding that test,” he says. “It’s typically a laminated glass with a PVB interlayer, structural silicone to ensure the glazing is tied securely into the frame and also looking at installation details to ensure the unit transfers all the load back into the framing system of the building.”

And while hurricane glazing products are commonly used in residential applications, that’s not the case when it comes to tornado glazing, he says.

Feasibility Issues

For this and other reasons, the majority of door and window manufacturers that produce impact- and hurricane-rated products who were queried for this article say they have yet to seek tornado ratings for any of their products. Most say that’s because the costs for tornado testing are high, while demands remain low. It’s a compound issue, suggests Terry Newcomb, marketing director for Thermal Windows Inc.

“It is possible to meet the requirements, with reinforced frames and polycarbonate glazing, but the cost of product design, testing and certification is quite high,” Newcomb says. At the same time, “The overall demand seems to be quite low,” he adds, “since the windows would be very expensive for the end user.”

So far, costs and demands are what have kept most manufacturers out of the tornado segment, even though it’s entirely possible that some of today’s
hurricane-rated products could achieve tornado ratings, suggests Jay Savage, marketing director for PandaWindows and Doors. “We may already
have systems that can achieve the ratings required for tornadoes, but we have yet to re-evaluate those products against the requirements to qualify
as ‘tornado-rated,’ because of so few requests,” Savage says. However, this could change going forward, he adds.

One factor that drives the cost for tornado testing, manufacturers say, includes the need for multiple units amid testing.

“The cost of testing is considerable, requiring a specific quantity of test specimens for each window and door type, of specific sizes, together with
lab and report fees, staff time and expenses,” says Pam Maurus, marketing manager for St. Cloud Window Inc. “Certification for tornado performance is not out of the question,” she adds, “but for the moment, is less of a priority than other performance and compliance objectives.”

Meanwhile, even representatives for some of the largest door and window manufacturers suggest that the concept of tornado-rated windows doesn’t necessarily make good sense for the residential industry in ways that go beyond costs. Because most residential structures are not designed to withstand tornados, windows might not be a good fit, argues Mark Montgomery, vice president of marketing for Ply Gem Windows. “It would take comprehensive integration into a hardened construction methodology before we would invest in testing and development,” he says.

And though tornado-rated doors have made their way into residential homes via safe rooms, among the half-dozen (mainstream) manufacturers interviewed for this article, none reported that they make such products.

On the commercial side, however, in Key Media and Research’s 2019 Glass and Glazing Industry Outlook, “impact resistant applications/products” was the second-highest industry trend (of 10) that glass fabricators say will affect their businesses over the next three years. This is a big jump from previous years, as this trend ranked in the bottom three in the 2017 and 2018 editions of the Outlook report. Insights suggest that fabricators may be gearing up to meet the continually heightened demand of hurricane-resistant products and other applications driven by more frequent storms and increased awareness for storm safety.

Need for Awareness

There’s a great deal of education that’s needed about tornado-resistant products to ensure their proper use, experts suggest. Codes is one of those

“We still run into confusion or a lack of knowledge sometimes with someone building a safe room, and not knowing that it needs to meet FEMA 361 [Safe Rooms for Tornadoes and Hurricanes: Guidance for Community and Residential Safe Rooms],” says Sagerman. “There’s confusion over whether hurricane also testing meets those requirements, but these requirements are so much greater for a safe room.”

According to Sagerman, one significant code change for tornado glazing includes the new requirement for manufacturers to have their testing verified through nationally recognized third-party labs, such as UL LLC, confirming that windows and doors meet the requirement.

“The test lab also makes quarterly, unannounced visits to make sure it’s being tested as inspected,” he says.

According to Kurtis Sullentrop, vice president of sales and marketing with Winco Windows in St. Louis, another misconception he’s seen relates to the
size of tornado windows.

“I think a lot of people think a tornado window will be very small, but it can be as large as a typical architectural window,” he says, adding that even though they are impact performance products, they still must also perform like a traditional window. “These products are focused on safety and security, but they still have to be a window 365 days a year. They still have to stop air and water and pass those tests.”

Right Product, Right Place

Probably the most critical consideration to stress is that hurricane and tornado glazing products cannot be used interchangeably. Having the correct product in the correct application is extremely critical and heavily dependent on a building’s use.

“Safe rooms are places of shelter. Those buildings are created so people can go there in case of a storm and they’re going there for protection,” says Sagerman. “It’s critical the windows, doors and the whole building are designed as specified. You need that clear understanding of the safe room design versus Miami Dade; that’s enhanced protection, and a safe room is absolute protection.”

Sullentrop agrees. “We want to ensure that people aren’t taking refuge behind something not suited for the storm from which they’re taking refuge,”
he says. “Hurricane glazing is there to protect the building envelope, because we assume that people have left the building. Tornado glazing is there to
save the lives of people, because they’re taking shelter in those safe rooms. They don’t want a false sense of security.”

Ellen Rogers is the editor of DWM’s sister publication USGlass magazine.
Drew Vass is editor of DWM magazine.

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