Window glass is a very hard but brittle substance traditionally made from a mixture of 72% silica + 14.2% sodium oxide (Na2O) + 2.5% magnesia (MgO) + 10.0% lime (CaO) + 0.6% alumina (Al2O3). This basic glass alloy is also used for display cases, tableware, furniture, light bulbs, jars and other containers. It exhibits great clarity but is also a poor insulator of both heat and sound.
Early in my career, I worked in the glass industry for over 2 years as a custom and production glass cutter and tempering oven operator in the field of glass tempering. I was involved in all phases of tempering, heat strengthening and spandrel production. A few years later, I held a position where I purchased high performance glass for a company that manufactured residential, commercial and structural skylights. I also know people who have worked for a very large impact window and door manufacturer here on Florida’s west coast. I mention this only to let you know that although I’m not an “expert” on glass, I have more than a layman’s knowledge of glass and I still keep abreast of the happenings in the glass industry.
Here is the current issue at hand………there is a slew of window companies out there who have employees/dealers misrepresenting the abilities and capabilities of impact glass windows. Contrary to what many window company salespeople have been stating to prospective customers:
- Impact glass is NOT indestructible
- Impact glass is NOT hurricane proof
- Impact glass WILL break from wind-borne hurricane debris
- Impact windows are NOT cheaper than standard windows w/impact shutters
- Impact windows are NOT the best form of hurricane protection
- You CAN go wrong installing impact windows
- Impact windows will NOT save you the most money in the long run
The simple truth is that impact glass windows are not the high-performance item that many salespeople would like you to believe. It is merely 2 pieces of window glass separated by a plastic film that has a clear gooey butyl sealant on both sides. It’s very similar to the glass found in automotive windshields and no matter what you do with it, it still breaks into tiny pieces and dust. Keep in mind that most impact glass doesn’t use tempered safety glass that is designed to break into round chunks. Somehow the impact glass industry has found a way to avoid the safety regulation that says safety glass (tempered safety glass) needs to be used in the windows of the 1st story of a building where breakage onto a pedestrian could occur.
So let’s call a spade a spade and put the cards on the table and call impact glass what it really is – sacrificial hurricane protection that is designed to break and sacrifice itself to maintain the integrity of the structure envelope. Then, after it is sacrificed (broken) it has to be replaced – PERIOD. There is no repairing it and it is no longer functional as a window. You can’t see through it and trying to open or close it will only make a bigger mess or result in injury.
After the storm has passed and your window has been impacted, the word that best describes impact glass is “junk”. If you have ever have an afternoon to spare and want an education on hurricane products, go to an impact testing lab and see what is left over after an impact window has been hit by a 9 lb. wood 2 x 4 at 34 mph (the current hurricane test standard). If you don’t think you will be able to see it in person, click here and here. The mess that it creates isn’t too bad until you realize that you’re standing in a huge building with concrete floors that are easily cleaned with a push broom and a shop vac. Unfortunately, your living room carpet won’t be quite so easy to clean. Your best bet is to replace the carpet because you will be hard pressed to get every minute piece of broken glass swept up – especially if some of the pieces have any of the gooey butyl sealant on them. And by the way, it doesn’t take very much force to break impact glass. That same board traveling at only 15 mph will still break the glass. The mess won’t be as big but the cost and inconvenience to replace the window will be the same. The best result that you can hope for is realizing that wind-borne debris will probably only hit one of your windows, right? Or how about a baseball from the boys playing outside, a golf ball from the tee box or a stone from the lawnmower??
Do yourself a big favor and the next time your window salesman says something like “…..having impact resistant glass windows and doors is an absolute must” or “with impact glass windows, homeowners don’t need to worry about making additional preparations such as shuttering the windows”, kindly escort him or her out of your home or, if your are in a store, turn on your heel and high-tail it out of there. The chances are that if he’s going to tell you one lie, he will probably not have a problem telling you more. When any salesperson has to mislead or not divulge critical information to a prospective customer to make the sale, that’s when I have a problem.
Don’t get me wrong, impact glass is good stuff – it’s just not the “hurricane savior” that many window folks would like to lead you to believe. I encourage all of my strip plaza and mini mall owners to have their full glass entrance doors replaced with impact rated units. What I don’t recommend is replacing all of their storefronts with impact glass. Why? Because they don’t insulate as well, reduce outside noise as well or resist large missile impact , smash and grab theft or vandalism attempts as well as Evolution Hurricane Shutters. Impact glass or windows will cost them way more, too, and when it’s all said and done you will still have the problems associated with glass breakage.
Like I stated previously, impact glass is a great product when used in it’s proper place. Storefront entrance doors and multistory commercial buildings are good applications. Any place where it’s not important or convenient to be concerned with breakage and replacement. Anywhere that the concern of energy conservation is outweighed by a certain architectural look or where the weight and energy costs aren’t important also makes impact glass a good choice. For the average homeowner or commercial property owner who is looking for a faster return on investment, energy savings, reduced interior noise and no breakage concerns, impact glass in the windows or storefronts might not be the best idea.
john sortore 