There’s a common misconception about impact windows: that they’re unbreakable. Don’t get us wrong, impact windows are incredibly tough. They’re designed to shrug off wind pressures and flying object impacts that would turn a non-impact window into a hundred shards of flying glass.
But, impact windows aren’t unbreakable. A hard enough blow can break an impact window’s glass. But that’s where the difference between an impact window and a non-impact window becomes clear: The impact window is designed in a way that minimizes the risk of a total breach.
Let’s go over some of what makes an impact window different from a non-impact window to enhance safety and protection:
Are Impact Windows Unbreakable?
Again, impact windows are not unbreakable. Like any object, there is an upper limit to the amount of force they can absorb. Once that threshold is exceeded, the safety glass used in the impact window will break.
Where an impact window differs from a non-impact window is what happens when the glass does break.
How Impact Windows Differ from Non-Impact Windows
An impact window is constructed differently from a non impact window in several ways:
- Safety Glass. Rather than annealed glass, impact windows are typically made of safety glass that has been tempered. Tempered glass is heat-treated, cooled, heated again, and cooled again repeatedly to increase the glass’ strength—typically making it 5x stronger than normal glass. Additionally, when safety glass breaks, it shatters into tiny, almost cubical pieces with dull edges to reduce injury risks.
- Laminate Interlayers. In addition to using heat-treated safety glass, impact windows have a layer of laminate between two safety glass sheets. The glass adheres to the laminate (usually PVB or a similar material) so that, if the glass breaks, the pieces stick to the laminate. PVB is a semiflexible material that can flex to absorb the impact and will help maintain the seal of the insulated glass unit (IGU) even when the top layer of glass is shattered.
- Multiple Layers of Glass. Inside the insulated glass unit of an impact window are multiple sheets of glass. Often, there are two or even three layers of glass inside the IGU. There’s the first two layers of glass that are joined with the laminate layer, then there is often another layer of safety glass separated from that as well. The gap between the layers of glass serves as a thermal break and also gives the laminate layer some room to flex without directly touching the other glass pane. This helps to prevent both panes of glass from breaking from the same impact.
- Reinforced Window Frames. Impact windows have structurally-reinforced frames to prevent warping of the frame from a collision with flying debris. In some cases, the frame itself is made of aluminum. However, for more modern, energy-efficient windows, the exterior of the frame is made of PVC with an aluminum core to reinforce the PVC. This provides extra sturdiness while preserving energy efficiency.
What Happens When an Impact Window Breaks?
So, what happens when an impact window is broken? Impact windows are designed with fail states in mind, creating redundant protective systems that help ensure that the inside of the home remains safe even when the top layer of glass breaks.
For example, in this video, you can see a person putting the impact resistance of an impact window to the test:
As you can see, while the top layer of glass spiders, cracks, and even significantly deforms with each blow of the bat, the bat doesn’t get past the top layer of glass.
Here’s what’s happening:
You can see that the area immediately around the location of the impact is full of crushed glass and bent inwards from the impact of the bat’s tip. Spider cracks radiate out from the point of impact, but with the exception of small chips, the majority of the glass remains in place.
This is because the top layer of the glass is directly attached to the laminate layer underneath it. The laminate holds the cracked glass in place, which forces the safety glass to be the first point of impact for each follow up strike. When the bat hits anywhere other than the exact spot where the majority of the top glass layer has already been shaved away, the force of the impact is distributed first through the glass before reaching the laminate.
The laminate itself, being semi-flexible, cushions the impact before the force is transferred to the layer of glass beneath it. This helps to reduce the force of the impact to the second layer of glass, minimizing damage caused by each blow.
After several impacts, the final pane of glass opposite the site of the impact remains undamaged, since the bat never reached it.
Now, given enough time, the person with the bat could eventually get through the window, but it would take a significant amount of time and effort.
How Does This Protect My Home During a Hurricane?
When confronted with a hurricane, it is rare for a window to take a direct, head-on impact like the one in the video above. Usually, storm debris strikes the walls and windows of your home at an angle, which already helps reduce the chances of the top layer of safety glass breaking.
But, even when the top layer of glass does get cracked, the laminate interlayer and the second layer of glass are there to preserve the seal of your home so that wind and rain cannot get through the insulated glass unit.
Larger objects may break the glass, but will then bounce away without penetrating the secondary layer of glass. Even if a large, sharp-cornered object strikes the glass and penetrates the top layer and the laminate underlayer somehow, there’s still the other glass pane on the inside of the window to keep your home sealed against the elements.
The maintenance of the seal is the most important part of the protection an impact window provides. It prevents hurricane force winds from being able to get into your home to act on the interior walls and underside of your ceiling/roof structure. This can lead to sudden structural failure as the wind lifts the roof off your home and the internal walls collapse from pressures they aren’t designed to withstand.
With any major hurricane, the wind hitting your home creates both a pushing force on the windward side and a suction force on the leeward side of the structure. Your external walls are designed to withstand this pushing and pulling force. Your roof is also designed to withstand a certain amount of this pushing and pulling force during a storm. The difference between the pressure in any two points of a system is called differential pressure, and homes can only withstand a set amount of differential pressure at any two points before something has to give.
As noted by hurricanescience.org, “Excessive differential pressures caused by wind flow on two, opposite sides of any building component (roofs, walls, structural beams, etc.) could deform or dislodge these materials when the differential pressures… exceed the resistance capacities of the components and/or their connection to other parts of the building.”
When a window breaks completely, the inside of the structure experiences a sudden change in air pressure proportional to the force of the storm. This massively increases the differential pressure experienced by the structure, as the internal pressure of the building adds to the pressure being experienced by its leeward side.
This is also why it’s important to keep your windows closed during a hurricane. Opening a window or door during a storm can compromise your home’s structural integrity.
Even absent the risk of sudden catastrophic structural damage, a broken window can let in water (including dirty storm surge water), insects, and road debris into your home.
Can Impact Windows Stop Home Invasions?
If the video of the person trying to break through a window was any indication, an impact window can stop an intrusion attempt… or at least significantly delay the time between an intruder starting their break-in and when they finally breach the window.
A lot of would-be criminals, once they realize that they aren’t going to be able to break the glass quickly and easily like they expected, may give up on their break-in attempt out of hand. Such was the case with an old, viral video by ABC 10.
In the video, a group of armed suspects attempt to break into a home, going so far as to shoot the glass of the impact-rated sliding glass door to the home. Despite repeatedly shooting the door glass, the intruders were unable to get inside, forcing them to give up and flee before authorities could catch up to the group.
The incident was caught on security camera and shared with news outlets:
While grainy (it is old footage), the video does a wonderful job of showing how impact-rated insulated glass units can frustrate would-be burglars to protect your home. Once they realized that even shooting the glass wasn’t working to get them in the home, they gave up and fled.
Although that door will need to be replaced with a new one because of the damage to it, that’s vastly preferable to needing to replace many more belongings or risking a member of your family being hurt by armed intruders.
Get Impact Doors and Windows to Protect Your Home
Impact windows aren’t invulnerable, but they are incredibly tough and can do a lot to reduce your home’s risk of moisture damage, pest infestation, and even total structural collapse following a major hurricane. Even outside of hurricanes, impact windows are a great security precaution that can discourage would-be intruders and buy your family precious minutes to call the cops during a break-in.
If you’re thinking about ways to make your home safer and securer, reach out to Karoly Windows & Doors to request a quote for impact windows and doors for your home. The sooner you can add this protective measure to your home, the better.
