The simplest answer to this question is that most home windows are tempered glass. However, there are some windows that may not be made of tempered glass for various reasons.
Before we jump into the nitty-gritty details of when and where tempered glass is required to be used, it may be helpful to break down the different types of glass and the accompanying pros and cons of each.
Annealed glass is probably what you imagine when you think of a simple pane of glass. It is also called standard glass because it is a simple form of manufactured glass that is used to make many other types and styles of glass. The cost of annealed glass is often lower than other types of glass.
Annealed glass is thermally treated to eliminate imperfections in the glass and then slowly cooled. This cooling process helps to get rid of tension on the inside of the glass. At this point, the glass can be cut and shaped into smaller pieces with more specific designs and styles, such as a beveled edge.
One issue with annealed glass is that it is much weaker than other types of glass that are often used for windows. If standard, annealed glass breaks, it shatters into large pieces that are very jagged and sharp. This is a safety hazard and makes the clean-up process very difficult and dangerous.
If there are no safety concerns and cost is an issue, annealed glass can be a good option. However, it is important to know if a stronger type of glass would be a better choice, like in the case of most windows.
Tempered glass starts out similar to annealed glass as float glass and is also heated and cooled. However, the tempering process differs dramatically from annealing, and the results are very different.
Tempering requires the glass to be cut into the correct size because once the glass has been tempered, it will not be able to be cut, drilled, or etched without shattering. Once the glass is the necessary size, it is moved to an industrial oven and heated to 620 degrees Celsius or 1148 degrees Fahrenheit. Once the glass reaches this extreme temperature, it undergoes a high-pressure cooling process.
This part of the tempering process is called “quenching” and lasts only a few seconds as the heated glass is blasted from all sides with pressurized air. Because the surface of the glass cools much faster than the inside of the glass, the interior attempts to pull away and creates tension inside of the glass as the outside compresses.
This tension is what gives the glass its strength and durability, as well as added safety. After completing this process, tempered glass is four times stronger than annealed glass and can withstand at least 10,000 pounds per square inch of force before breaking. Additionally, when tempered glass does break, it shatters into smaller pieces that have much duller edges than the jagged shards of annealed glass.
Because of this, tempered glass is also commonly referred to as safety glass and is required for many construction projects. It is also more expensive than other less highly manufactured glass but can make a huge difference in the strength and safety of whatever product is created using tempered glass.
Another choice for home windows is impact-resistant glass. This particular glass is made with polyvinyl butyral (PVB) that creates a thin film (between .015 and .09 inches) between two layers of glass. The layers of glass can be tempered glass, but that is not always the case.
Impact-resistant glass is not immune from breaking, but when an impact-resistant pane of glass breaks, the polyvinyl film keeps all of the pieces together and prevents debris from getting through the window. This can be important for homes that are located in areas prone to natural disasters such as hurricanes and tornados.
As the name implies, double-pane windows are made from two sheets of glass that are put together with a very small space between them. In the case of impact-resistant windows mentioned above, sometimes specific materials can be placed between the two panes, or some double-pane windows use tempered glass for either one or both of the panes, but that is not necessary for all double-pane windows.
Whatever materials are used, double-pane windows have many advantages. They offer insulation for your home, which can lower your energy bills. They also buffer sound from either side and can even include a UV-protectant.
So with all of these different choices for glass to use in your home windows, how do you know which type of glass to choose? Well, in many residential codes, there are specific requirements for tempered glass to be used for both safety and durability.
Where Is Tempered Glass Required?
Did you know that there is an International Residential Code that lays out requirements for all standalone residential dwellings? This IRC was put in place by the International Code Council, whose purpose is “to safeguard the public health and safety of all in communities both large and small.” According to the IRC, all glass that is installed in any door and within 24 inches of a door is required to be tempered glass.
There are some states that have even more stringent building codes that require tempered glass in any area that has running water, is next to stairs, or is within three feet of a walkway. If there is a window or mirror that does not fall under any of those conditions, then the tempered glass is not necessary. However, many contractors may still recommend tempered glass for your home windows.
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