Tom Shafer

6 common questions about tempered glass

September 09, 2015

I was training a new salesperson for a customer recently and the question of tempered glass came up. I had to explain how it was made, what it did, and where it's used. And it occurred to me that if even industry pros don't always know how to explain these windows, how could a homeowner? So here are six of the questions we hear most often about tempered glass.

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  1. Where is tempered glass used? Tempered glass is in all kinds of doors - entrance doors, storm doors, shower doors, interior doors, French doors, and some cabinet doors. It is required by building codes. A general rule of thumb is tempered glass is required wherever there is a possibility of a person falling into it.
  2. How is tempered glass made? A tempering process for any hard material is basically the same. The material is heated to a very high temperature (it varies by material) and then is cooled very rapidly. In the case of glass, it is heated until it glows orange, then is cooled by blowing very cold air across its surface. This makes the surface very hard.
  3. Is tempered glass unbreakable? NO! It is not. While the surface is very hard, it will break with impact and pressure. However, because of the tempering and the shock it is subjected to during manufacturing, it breaks into small pieces. It does not break into large and potentially lethal shards.
  4. Is it expensive? Tampered glass costs about one and a half to two times more than non-tempered glass. While this may seem expensive, it's a worthwhile investment if it prevents a lethal accident.
  5. Is it safety glass? While some refer to it as safety glass and it does afford a measure of safety, it is not safety glass. Safety glass is generally a laminated glass. Your car windows are safety glass. While tempered in most cases, it also has a layer of clear vinyl fused between two pieces of glass. When laminated safety glass is broken, it stays together. The glass does not crumble.
  6. How can you tell if a window has tempered glass? All tempered glass is required to have a small mark etched into the glass. This is required by code and is usually easily seen.

Be assured when you see that logo, or one similar, the glass is tempered. Check your home see which windows and doors have tempered glass. You might be surprised.

About the Author

Tom Shafer has decades of experience in window sales, marketing and product development. He's worked closely with window design engineers in testing, design, and building code interpretation. Past employers include United Windows and Doors and Norandex, MI Windows. He currently works at a home improvement retailer.


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