Understanding the Differences in Hurricane and Tornado Glazing Products

By Ellen Rogers

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

That’s how Dean Ruark, vice president of engineering and product development at PGT Industries, puts it. And he’s not alone. Others in the protective glazing field agree that, though both are impact products, tornado glazing is in a class of its own.

Why? “A tornado is a different animal,” says Gerry Sagerman, who works in sales development for Insulgard Security Products.

And different animals require different approaches.

While hurricane glazing products are well-established in the marketplace, tornado products are still relatively new, and there is still confusion and misunderstanding surrounding their use. Depending on the region, state or jurisdiction, certain applications call for certain products, and it’s all 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 against which the products are protecting. 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 window or door is breached during a hurricane, wind and rain can penetrate the building and cause structural damage. 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 windows and doors 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 a tornado safe room system is a 15-pound two-by-four shot at 100 mph, compared to Miami-Dade hurricane windows, which are tested with a nine-pound two-by-four shot at 34 mph. That great amount of impact [in the tornado test] is more than 10 times the amount of load compared to Miami-Dade.”

The tested tornado system is made up of glazing, such as glass-clad polycarbonate, framing and anchorage of the frame to the wall.

“The glass must stop the two-by-four, allowing no spall to the interior/safe side,” says Sagerman. “The glass must stay in the frame and the frame must stay in the opening.”

Sagerman says there are similarities in testing for tornado and hurricane
glazing, but also some key differences.

“They both require structural pressure testing and impact testing, then, for hurricanes, the impacted specimen must complete cyclic testing,” he says. “You have to make sure the debris-impacted windows will stay in place for the remainder of the storm, as hurricanes last 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.”

Clearing Through the Confusion

Building safety continues to be a focus in both commercial and residential construction. In hurricane-prone regions, building codes mandate the use of high-impact materials and the incidences of hurricane glazing continues to increase.

In Key Media & Research’s 2019 Glass and Glazing Industry Outlook, “impact resistant applications/products” was the second-biggest industry trend (of ten) 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 heightened demand of hurricane-resistant products and other applications driven by more frequent storms and increased awareness for storm safety.

Though still not as widespread as hurricane products, awareness and use of tornado glazing is also increasing. As a result, there’s a great deal of education that’s needed.

“We still run into confusion or a lack of knowledge sometimes with someone building a safe room, and not knowing what is required of product testing to meet FEMA 361 [Safe Rooms for Tornadoes and Hurricanes: Guidance for Community and Residential Safe Rooms],”says Sagerman. “There’s confusion over whether Miami-Dade hurricane testing also meets those requirements, but these requirements are so much greater for a safe room.” He explains that FEMA 361 provides guidance from the Federal Emergency Management Agency (FEMA) about the planning, design, construction and operation of tornado and hurricane safe rooms, and in some cases references ICC 500.

According to Sagerman, one significant code change for tornado safe room windows includes the new requirement that manufacturers have their products labeled by a nationally recognized lab, such as UL, certifying that the windows and doors meet the requirement.

“As part of the certification, the test lab also makes quarterly, unannounced quality control visits to make sure it’s being manufactured as it was tested,” he says.

Ruark says water performance is another detail often misunderstood.

“It’s important for people to understand the water performance of products and what they go through during a Testing for impact windows used in tornado safe rooms requires a 15-pound major storm,” he says. “The industry has an opportunity to educate the home-owner so they understand that there are different water ratings on products, but they aren’t as heavily discussed.”

There are also misunderstandings when it comes to impact performance.

“For example, Dade County is a lot more stringent than the ASTM standard when related to hurricane products,” says Ruark, explaining that ASTM only requires the glass to be struck once with a missile, whereas Dade County requires two strikes to the glass and [once] to the framing member.

“Some people still think if they have impact windows and it gets struck that it won’t break, and that’s a misconception,” says Ruark. “The real benefit is it adheres to the interlayer and resists the wind from coming inside.”

Kurtis Sullentrop, vice president of sales and marketing with Winco Windows in St. Louis, says one misconception relates to the size of tornado windows.

“I think a lot of people think a tornado window must 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

Hurricane and tornado glazing products cannot be used interchangeably. Having the correct product in the correct application is 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 for that purpose. You need that clear understanding of the safe room design versus Miami-Dade; that’s enhanced protection, and a safe room is near absolute protection.”

Ruark adds, “You can’t just take a hurricane window and put it in a tornado zone. That window has nowhere near the same testing requirement and the essential facility would be rendered unusable post tornado.”

Sullentrop agrees, “We want to ensure that people aren’t taking refuge behind something not suited for the storm from which they’re seeking protection. 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.”

Increasing Awareness

The need for and focus on awareness for hurricane glazing products has grown for nearly 30 years. Over the three decades since Hurricane Andrew, products have gotten stronger, as have related codes.

“There’s been a lot of evolution in hurricane impact products and they’re becoming more common in buildings, post Andrew,” says Ruark, adding he’s also seeing increasing awareness around tornado products.

“Those products aren’t yet mainstream,” says Ruark. “But I think there’s more and more discussion in the industry around protective glazing, and there are discussions with laypersons that hurricane windows are not the same as tornado windows.”

There’s at least one difference, though, between the two products that Sullentrop doesn’t expect to change.

“…It’s specialty glazing companies that are focusing on tornado products. We’re not seeing most companies getting into the market the way they did with hurricane glazing, because this requires such a higher level of testing and involvement,” he says. “This will always be a niche market.”

Ellen Rogers is the editor of USGlass magazine. Follow her on Twitter @EllenGRogers and like her on Facebook at usgellenrogers to receive updates.

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