How-To

What is Hurricane Impact Glass?

Windows and doors reinforced with impact glass can help protect your property and your family from the devastating effects of hurricane-force winds.

August 15, 2022

Hurricane Windows

A category 2 hurricane can produce 110 mph wind speeds—that’s enough to flip a parked car. A category 5 hurricane can generate wind speeds of more than 155 mph—that’s enough force to tear apart a home and seriously threaten the lives inside.

If you live in a region threatened by hurricanes and tropical storms, your best defense is a well-built home that has properly installed windows and doors reinforced with impact glass. Today’s impact glass is a marvel of modern engineering and can withstand an astonishing amount of abuse. Here's a helpful article that will explain how impact glass is made, why and where you might need it, and which materials to look for when sourcing the highest quality hurricane-resistant windows and doors.

What is Tempered Glass?

Impact glass is comprised of two different types of glass, one of which is called tempered glass, also known as safety glass. Tempered glass is manufactured in a way that makes it up to four times stronger than annealed (standard) glass. Also, when tempered glass is broken, it splinters into tiny pieces instead of large, sharp shards, which reduces the chance of serious injury. For these reasons, residential building codes require tempered glass for windows in areas where there’s an increased chance a person could slip, trip, or fall. Windows installed close to the floor, in stairways, and near tubs and showers are a few common examples. The glass installed in doors and in windows is also required to be tempered.

A home in the coastal southeast featuring Marvin Coastline Casement windows.

Photo by Cornerstone Companies

What is Laminated Glass?

Impact glass is also comprised of laminated glass, which is constructed by sandwiching a near-invisible sheet of plastic between two panes of glass. Laminated glass adds some strength to a windowpane, but the main benefit is that when laminated glass breaks, the plastic holds the broken pieces together. This tough plastic layer can also prevent projectiles from passing through windows and into a home, reducing the chance of injury. The auto industry was one of the first to embrace the use of laminated glass to prevent drivers and passengers from being thrown from a vehicle during an accident.

Marvin Coastline Outswing French Door leading out to a porch.

Optical Distortion in Heat-Strengthened and Tempered Glass

The use of high-performance glazing, such as laminated heat-strengthened glass, enables windows and doors to withstand harsh coastal conditions. Engineering glass to perform under extreme conditions can create optical characteristics and distortions that occur as a result of the strengthening process required for these types of glazing.

What is Optical Distortion?
Optical distortion happens when an object viewed through the glazing may appear to have a “wave” or “bend” due to the lensing effect of the glass. Generally, this effect is more pronounced when viewed from an angle.

What Causes Optical Distortion?
Optical distortion can be caused by the heating and quenching process that glass undergoes to produce the increased strength characteristics required for many applications. Glass is passed through an oven and heated to the point of softening. Air blowers then rapidly cool the surface of the glass as it leaves the oven in a process called quenching. This rapid cooling places the surface of the glass under compression. The surface compression increases the strength of the glass to four to five times over the strength of standard annealed glass for tempered glass, and approximately twice as strong as annealed for heat strengthened glass. However, the surface compression can also induce a slight waviness to the glass as it is rapidly cooled. This waviness can result in optical distortion. At high temperatures the glass is subject to during heat treating, glass is also more susceptible to roller waves, bow, and warping. Optical distortion is not a defect, but rather a result of the strengthening process.

Impact Glass is the Best of Both Worlds

Impact glass, sometimes referred to as impact-resistant glass or hurricane glass, is safety glass on steroids. The most resilient impact glass combines both tempered and laminated glass into one double- or triple-pane unit. And both the plastic laminations that hold the glass together and the tempered panes of glass themselves are often thicker than standard glass. Impact-resistant glass is tested by recreating the effects of wind speeds of more than 100 mph. Glass and window companies test windows and doors reinforced with impact glass by launching 2x4s at them at speeds of 35 mph and blasting them with steel balls at near 90 mph.

What are the Benefits of Impact Glass?

Choosing to install impact glass in your impact windows and doors can prevent windborne debris, generated from severe storms, from crashing into your house and causing property damage and serious injury. And while preventing that street sign down the block from landing on your couch is a good thing, it’s not the debris that poses the biggest risk to your home and family, it’s the hole the debris leaves in the window or door. If all the windows and doors in a house are sealed up tight, it’s more likely the storm winds will blow over and around the building as if it were a solid block. But if a window or door should be smashed open, that wind will blow into the house and could create such high pressure it might cause the house to blow up and expand just like a balloon. Since houses are not made to expand like a balloon, this high pressure can result in walls being knocked down and entire roofs being blown off a home.

In addition to creating a protective barrier that could prevent devastating storm damage, impact glass has other advantages as well. The thicker glass and sturdy laminations make impact glass an effective defense against forced entries. Just google “impact glass testing” and you’ll find some amazing videos of impact glass withstanding abuse from baseball bats, sledgehammers, and crowbars. Another often overlooked benefit of impact glass is that it does a significantly better job at sound dampening than standard annealed glass. So, if your home is located near an airport or on a busy road, impact glass could be a great solution to create a more peaceful indoor environment.

A Marvin Coastline Garage Door and a Marvin Coastline Window Wall.

Why Not Plywood, Shutters, or Storm Windows?

Installing plywood over windows and doors can be an effective way to protect your home from a hurricane. However, the problem with sheets of plywood is that someone must install them, and then take them down, and then install them again before the next storm hits. It’s not uncommon for the Southeast Coast to experience more than one hurricane in any given season. And who will install the plywood if you’re traveling or if your house is strictly a vacation getaway that you only visit in the winter? Trying to find a repair person to install them could be nearly impossible, because you won’t be the only one who needs help. Installing plywood over windows and doors also leaves unsightly screw or nail holes in the exterior that will need to be repaired. And finally, plywood sheets need to be stored when not in use, hurricane-resistant windows and doors do not.

There are shutters on the market that will effectively stop windborne debris on standard-sized windows, but they might detract from your home's architecture, especially if you’re looking to achieve a modern aesthetic with clean lines. And just like plywood, storm shutters don’t work if they are not secured, and someone needs to be home to shut them. Also, standard shutters won’t protect large scenic doors and windows or garage doors.

What about storm windows? The name storm window is misleading. Storm windows, sometimes called storm sashes, are secondary glass or transparent coverings designed to work in conjunction with an existing single-pane window. Storm windows are not as common today because for several decades, residential windows have been made with more efficient, double-pane glass. However, storm windows are still available, and they can increase energy efficiency and reduce noise transference, but storm windows provide little or no protection against extreme winds and windborne debris.

Do you Need Impact Glass?

If you live near the Gulf Coast, in Florida, or along the Eastern Seaboard where hurricanes are a real threat, then choosing windows and doors with impact glass may be a sensible decision. In fact, it may be required. The building code in many counties located in hurricane-prone areas in the United States requires impact glass in new homes, and in existing homes receiving replacement windows and doors. If you or the contractor you’re working with are not sure if your home is in such an area, have a conversation with your local building official. If you live in, or are planning to move to, the state of Florida, be aware that the counties in Florida have the most stringent hurricane-related building codes in North America.

Not All Impact-Resistant Windows and Doors are Created Equal

Window and door companies typically don’t make their own glass, and there are only a handful of glass manufacturers that supply most of the residential glass in North America. All these manufactures make high-performing impact glass. But glass is not the only component that goes into a high-performing hurricane-resistant window or door. Window and door jambs and sash frames are what holds everything together. If you buy a window or door with the highest quality impact glass, but the other components are weak, you’re not getting the most resilient protection available.

A bedroom in the coastal southeast featuring Marvin Coastline Multi-Slide doors.

Impact windows and doors made of materials such as pultruded fiberglass, aluminum, or clad aluminum (wood wrapped in aluminum) are stronger, especially compared to their vinyl counterparts. For example, there is a reason automobiles, airplanes, and bridge structures are made from metal and not plastic. Not only is aluminum stronger and better at resisting direct hits from flying debris, but aluminum is also more stable. High temperatures and direct exposure to the sun can weaken and distort vinyl, seriously compromising its integrity. If you’re looking for the sturdiest, long-lasting hurricane-resistant windows and doors, then it is important to consider both the glass and the material makeup of the window and door components.

Proper Installation is Key

Installing or replacing standard windows and doors is not a typical DIY project. A shoddy installation can void a warranty and lead to poor energy performance, bad operation, reduced product life, and increased risk of water infiltration that could lead to rot and the growth of harmful molds. Plus, you don't want to get to the final inspection and find your window or door installation doesn't pass, creating unexpected delays and additional expenses.

That said, a person with extensive knowledge of water management who strictly adheres to manufacturer’s instructions can pull off a standard installation. However, the proper installation of impact-rated windows and doors is even more important given the considerable abuse they might be subject to during a high-category hurricane. It’s usually best to work with a competent, experienced installation contractor who has intimate knowledge of the homes in the area, the local building code requirements, and the windows and doors they install.

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