Windows are vulnerable to high winds, but no single wind speed breaks all windows. A window’s vulnerability depends on a complex interplay of various factors. Understanding these elements helps explain why some windows withstand powerful storms while others fail, as numerous variables contribute to a window’s resistance.
Factors Influencing Window Breakage
The type and thickness of glass significantly influence a window’s resilience. Annealed glass, the standard type, breaks into large, sharp pieces and is least resistant to impact. Tempered glass is heat-treated to be four to five times stronger than annealed glass, shattering into smaller, less dangerous pieces. Laminated glass consists of two or more panes bonded with a durable interlayer, which holds the glass together even if it shatters, preventing dangerous shards from scattering. Hurricane-resistant glass is a specialized type, often incorporating laminated features, designed to withstand high winds and flying debris.
Window size and shape also play a role in their susceptibility to wind damage. Larger windows, such as expansive glass walls or commercial storefronts, experience more wind pressure than smaller ones, increasing their vulnerability.
The material and integrity of the window frame contribute to its overall strength. Aluminum frames are strong and lightweight, suitable for larger openings, and can be corrosion-resistant. Vinyl frames are popular for their affordability and moisture resistance, offering good insulation, though they may not match the strength of aluminum in severe conditions. Fiberglass frames, made from glass fibers in a resin matrix, offer strength, durability, and resistance to warping. Wood frames provide good insulation but require more maintenance.
Quality of installation is important; even the most wind-resistant window can fail if not properly sealed and anchored. Building exposure and location greatly affect wind forces. Buildings in open terrains, like coastal areas, face higher wind speeds compared to those in urban or suburban areas where nearby structures offer some sheltering effect. Wind pressure increases significantly with building height, making windows on higher floors more susceptible to damage.
Wind characteristics, such as sustained speeds versus sudden gusts, also impact window vulnerability. Sustained wind puts continuous stress on windows, while gusts create rapid pressure fluctuations. Wind direction influences how pressure is exerted on a building. Beyond direct wind force, airborne debris presents a significant threat; items like tree branches, outdoor furniture, or even roof tiles can become projectiles, lowering the wind speed needed for breakage.
How Windows Fail Under Wind Stress
Windows fail under wind stress primarily through pressure and impact. Wind creates pressure differentials on different sides of a window. The windward side of a building experiences positive pressure, pushing the window inward, while the leeward side and sometimes the corners can experience negative pressure, or suction, pulling the window outward. This pressure difference can exert significant force on the glass, potentially leading to breakage.
Under sustained wind pressure or rapid fluctuations, glass can begin to flex. This flexing, especially in larger panes, can cause fatigue over time and eventually lead to failure, even without direct impact. The constant changes in pressure can also stress window seals, leading to their deterioration and compromising the window’s integrity.
Projectile impact is another common cause of window failure during high winds. Objects like branches, outdoor furniture, or even loose construction materials become wind-borne debris, striking the glass at high speeds. This direct impact often results in shattered or cracked glass, compromising the window’s effectiveness.
In some cases, the window frame itself can fail before the glass. The force of strong winds can cause structural damage to the frame, leading to the glass dislodging or breaking. This frame damage may not always be immediately visible but can affect the window’s stability and energy efficiency over time.
Protecting Windows from High Winds
One effective measure for protecting windows against high winds is installing impact-resistant windows. These windows feature laminated glass, where a strong polymer layer, typically polyvinyl butyral (PVB), is sandwiched between two panes of glass. This construction holds the glass together even if it cracks or shatters upon impact, preventing debris and wind from entering the building. Impact-resistant windows also often have heavy-duty, reinforced frames made from materials like aluminum, vinyl, or fiberglass, which are securely fastened to the window frame.
Applying window films also provides a layer of protection. Safety and security films, typically 8 to 9 mil thick, are applied to the interior side of the window. While the glass may still break, the film helps prevent shattered glass shards from scattering and becoming dangerous projectiles within the interior. These films can absorb and dissipate the energy from impacts, holding the glass in place and acting as a barrier against wind, rain, and water intrusion.
For temporary protection, boarding up windows with plywood or installing storm shutters offers a physical barrier against wind and debris. These methods help shield the glass from direct impact and the forces of high winds.
Securing outdoor objects significantly reduces the risk of window damage. Items such as patio furniture, grills, trash cans, or garden ornaments can become dangerous wind-borne projectiles during a storm. Bringing these items indoors or securing them to the ground can prevent them from striking windows.
During severe weather events, it is advisable to stay away from windows. If a window breaks, shattered glass and incoming debris can pose a serious safety risk to anyone nearby. Moving to an interior room, away from exterior walls and windows, can provide a safer environment until the storm passes.