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Can Impact Windows Break? Understanding Hurricane Glass Strength

Posted by Jimmy Hawley on Nov 5, 2020 8:45:00 AM

new-impact-window

You’ve probably heard Floridians talk about their hurricane windows and how strong they are. These impact windows were designed to withstand high winds, blunt force objects, hailstones— you name it. 

But how strong is impact glass, really?

There are lots of storm preparation myths that suggest that impact glass isn’t that sturdy. Some say that taping your windows or putting force against the glass can combat crackage or breakage— but these hacks have been proven wrong.

Luckily, impact glass is so sturdy and reliable that strength in most common storm conditions shouldn’t even be a concern— and in this post, we explain why. While impact windows do come in a variety of strengths, most base models offer heavy-duty protection, with options to increase your glass’ integrity for stronger winds. 

Let’s start by learning more the different areas and storm conditions that impact glass is designed to withstand:

Understanding Zone Ratings & Hurricane Categories

While all impact glass is “strong,” every pane can be made differently based on the strength you require. For instance, a storm window designed to withstand Category 2 hurricane forces is not the same window frame or glass that is intended for Category 4. (To understand the different hurricane categories, read our blog). 

That’s because storm categories are rated based on wind speed miles per hour, and glass is designed to withstand the impact of objects at specific speeds, simulating how debris could be hurled at your windows by violent hurricane winds. For example, here at Storm Solutions, our CGI-produced windows can withstand the pressure of up to +55/-65 pounds per square foot, but every window is different.

Here’s a look at our PGT hurricane windows being put to the test for Miami-Dade protocols against Category 5 storms:

Here in SWFL, windows that meet design pressure standards for Zone 4 or Zone 5 winds usually meet the strictest of Florida Building Codes. When shopping for storm-resistant impact windows in Florida, look for a manufacturer with documented NOAs (Notice of Acceptance by Miami-Dade County) for their products. 

Keep in mind that different counties require different levels of protection. When shopping for impact windows, it’s important to confirm they are rated for your High Velocity Hurricane Zone. A trained impact-certified hurricane window specialist can offer the best recommendation for your area. 

What Makes Impact Windows so Strong

Impact windows are designed and constructed very differently than traditional windows. In our storm vs. traditional window comparison post, we discuss how impact-resistant windows are often made of both tempered and laminated glass and ultra heavy-duty framing, which gives them their extra strength. 

If you read the article, you’ll learn that tempered glass is heated and cooled to thicken and increase its durability, while laminated glass is created by bonding two or more panes of glass with a thin layer of film or vinyl in between. That means most impact windows have not one but two layers of protection, and a film in the center of laminated glass to ensure that even if the window does crack, it will not shatter and fling dangerous shards across your home. 

For fun, here’s a video of us slamming a window with all our might at an impact window. As you can see, the glass splintered, but it does not shatter or fall out at all.

We recommend reading our linked post above, as well as The Differences Between Tempered, Laminated & Hurricane Impact Glass for a more detailed introduction to how impact windows are designed.

Determining Your Window’s Design Pressure

Design pressure is the amount of pressure put on your windows during a hurricane, which is important to understand, as this rating represents the maximum positive and negative wind load that your window can experience without breaking. The Florida Building Code requires that all newly installed windows meet a minimum design load.

Computing the minimum design load is a task usually performed by structural engineers that consider factors such as wind speed, exposure, the slope of your roof, and roof height in comparison to the width and height of your window or door. 

Basically, the higher the design pressure rating, the more resistant it is to the effects of wind and other pressures— so you want a higher rating. Learn more about design pressure here.

More on Impact Windows

Curious to see if your windows are impact-resistant? Here are five ways to tell if you have storm-ready windows.

Ready to start shopping for impact-safe glass? Here are the best rated hurricane windows for Florida homes. 

If you’re still on the fence about investing in impact glass, download our free ebook, 12 Things You Need to Know About Impact Windows, to discover all their benefits for yourself!

Tip Sheet: 12 Things You Need to Know About Impact Windows

Topics: Impact Windows