After the Storm
Windows and doors play an important role in the growing study of resilience for buildings
March 4, 2020
Natural disasters often spur conversations around resiliency in building, but the term can be vague and broadly defined. The National Academy of Sciences defines resilience as “the ability to prepare and plan for, absorb, recover from and more successfully adapt to adverse events.”
Ryan Colker, vice president, innovation and executive director for the Alliance for National and Community Resilience, an International Code Council initiative, explains there are two categories to consider in resilient design. The first is shocks, such as hurricanes, earthquakes, flooding and other natural events; the other is stresses, such as affordability, aging population and population growth. Fenestration and other building professionals primarily concern themselves with building resiliency as it relates to shocks.
Although shocks occur at a defined point in time, the exact time is variable and rarely has significant lead time. Therefore, preparations must be proactive. “We have to prepare when it makes sense to do so,” says Colker. “Certainly, we can design new buildings to address those particular shocks.”
When it comes to wind-related events such as hurricanes and tornadoes, Colker says the weakest parts of a building include the roof, doors and windows. “In wind events, it’s all about pressure, where that pressure is applied and how it can build up and get into a building,” he explains. Strategies to protect windows against flying debris, says Colker, can include the structure of the window itself or ancillary products like shutters.
“We’re also seeing potential opportunity around energy efficiency and the intersection with resilience,” says Colker. Some energy-efficient offerings, he says, also can have enhanced integrity depending on what films are used or if the window comprises multiple panes. Enhanced insulation values also could help keep families in their homes longer in extreme hot or cold events instead of forcing them to evacuate to shelters.
As awareness increases around resilient design, impact-resistant windows are evolving accordingly. Dean Ruark, vice president of product management and engineering for PGT Innovations, recalls when PGT launched a Miami-Dade County approved glass window impact-resistant product in 1994, it was a “specialized, niche” product.
That specialty niche product served a big market need, though, and, as such, spurred better engineering and technology. Materials also reached a more economical price point compared to early versions. In fact, says Ruark, there isn’t a huge price difference between an impact-resistant window and a non-impact window when homeowners have to add all of the storm shutters and hardware required to transform it into an impact-resistant product when necessary.
In addition, aesthetics have had “meaningful change,” with narrow sightlines and maximizing the glass while maintaining strength. “We’ve seen this transition from a tank of a product to something that really beautifies the architectural elements of a home with big openings and lots of glass,” Ruark says. “It lets the outdoors in, but when it’s time for the storm, protects you from those same elements.”
Regardless of geography, all buildings are designed to withstand some level of wind speed, which is one component of calculating design pressure, along with the shape of a building and surrounding terrain. The American Society of Civil Engineers conducts modeling based on probabilities of wind affecting a given area over a period of time, and high wind speed probabilities correlate to higher design pressures, Ruark explains.
Impact-resistant products come into play in wind-borne debris regions, defined as wind speeds exceeding 130 mph within 1 mile of coastal mean high tide, or wind speeds exceeding 140 mph regardless of distance from coastal mean high tide.
Ruark also says that the design pressure of a window correlates to the water infiltration performance. “Water is tested to 15 percent of the positive design pressure, so if you have a requirement for 50 DP, that will be rated for 7 ½ PSF of water,” Ruark explains. “But if you increase the DP requirement to 80 or 100, you get a much higher water performance in accordance with that.”
Ruark is part of a team of experts, including engineers, universities, FEMA and the National Science Foundation, that evaluates hurricane damage in the storm’s immediate aftermath. The teams see multiple areas and, within a defined grid, conduct random inspections and forensic assessments on structures. They detail each building, construction type, roof shape, year built, general details and document elevations and note a level of damage to a building.
“Through that effort,” Ruark explains, “we end up with a tremendous amount of data points on different buildings post-storm and how they performed. We try to glean common elements in the buildings that failed and common elements that performed. All of that rolls up toward different recommendations into how we make buildings more resilient in the future.”
Historically, building codes have been developed with immediate life safety in mind, says Colker. But, he points out, the events of today are not the events of tomorrow. “We’ve seen an increase in the number of severe events and the severity of those events,” he says. In fact, the frequency of the most damaging hurricanes has increased 330 percent century-over-century, according to a report published last year from the National Academy of Sciences of the United States of America.
“We need to think about how to address changing risks in a way that we may not necessarily know how they’re going to change,” Colker says. Climate models can provide some insight as to where to build in adaptability and where to make strategic investments that make building-enhanced resilience cost-effective. “It’s something the broader industry has recognized as something that needs to be addressed,” he says.
Although stronger buildings can be pricier, evidence suggests it is well worth the investment. The National Institute of Building Sciences Natural Hazard Mitigation Saves: 2018 Interim Report studied baseline building codes and found a benefit of $10 in mitigation benefits against hurricane winds for every $1 spent in adopting the 2018 International Building Code and International Residential Code. Above-code programs discovered a 4:1 dollar benefit. “There’s certainly a recognition that initial investment provides a significant level of benefit down the road,” Colker says.