When you’re shopping for skylights, you have to choose between acrylic and glass. But if you have already decided that glass skylights are right for you, you have another decision to make–laminated vs tempered glass. These are two different glazing treatments that are used to make glass skylights. They increase the impact resistance of the glass, among other benefits.
About Glass Glazing
Skylights are required to be made with safety glass, and for good reason. If a branch, stone, or other piece of debris hits the skylight with enough force, it could break the glass. Shards that careen down from the ceiling could quickly become dangerous to anyone standing below. Glazing is a safety feature that reduces that risk.
Many people misunderstand what the term “glazing” means when it comes to glass skylights. You might think that glazing is a coating that is applied to the exterior of the glass. However, it actually refers to the way that the glass is processed. Glazing involves putting the glass through a controlled chemical or thermal treatment to strengthen it and reduce the chances that it will cut someone if it breaks.
Untreated glass is referred to as “annealed” glass. The two types of glazing that are used for skylights are tempered and laminated glass.
Tempered Glass Basics
Tempered glazing is used for many applications, including skylights, automobile windows and exterior doors. If you have ever seen glass from a motor vehicle accident on the side of the road, you have witnessed what happens when tempered glass breaks. Instead of shattering into sharp shards, it breaks into small, pebble-like chunks. Although the broken bits can cut you if you handle them the wrong way or apply a lot of pressure to them, they’re not likely to cause severe damage.
To make tempered glass, manufacturers place it in an oven that heats the material to about 1,148 degrees Fahrenheit. After it comes out of the oven, the glass is cooled under a high-pressure process for a few seconds.
This method involves blowing air across the glass from different angles. It cools the material quickly, but it doesn’t reduce the temperature evenly. The outer surfaces will cool down faster than the core. As the temperature of the interior drops, the core contracts more than the surface. This creates compression in the outer layers, which strengthens the glass and creates distinct nugget-like shapes when it breaks.
Chemical tempering is an alternative process that’s used to make tempered glass. This process involves forcing compression via an ion exchange from certain chemicals. This type of glass is even stronger than heat-tempered glass. However, this method is not typically used for glass skylights.
When tempered glass breaks, it doesn’t always fall out of the frame. In some cases, it will shatter into a web-like network of cracks but remain in the skylight frame. If it does break, the pieces won’t be as sharp as shards of regular glass.
Laminated Glass Basics
Laminated glass is often used on car windshields, glass walls and high-security areas. Laminated glazing is a process that involves sandwiching an adhesive material between at least two layers of glass. The adhesive layer is known as polyvinyl butyral, or PVB. When the glass is pressed and bonded to it, the entire sheet becomes more impact-resistant. If more than two layers of glass are used, there will be a PVB layer, which acts as a clear plastic film, between each sheet.
PVB is flexible, which means that it can be used to create curved glass pieces. If the glass breaks, the shards stick to the PVB. The material will stay in the skylight frame without falling into the space below it.
When laminated glass is made using sheets of tempered glass, the chances that it will hurt someone if it breaks are even smaller. Even if the broken pieces separate from the material, they’ll be shaped like tempered glass nuggets.
Laminated vs Tempered Glass Skylights
There are some distinct similarities and differences between laminated and tempered glass. Here’s the breakdown in a nutshell.
- Both are a type of safety glass.
- They are stronger than regular, or annealed, glass.
- Both block UVB rays.
- Installation doesn’t require any particular time or effort.
- Tempered glass is made from a single sheet, whereas laminated glass is made from multiple layers.
- Tempered glass shatters into small chunks; laminated glass cracks but doesn’t separate when it breaks.
- The PVB in laminated glass blocks UVA rays, but tempered glass doesn’t.
- Laminated glass has better soundproofing abilities than tempered glass.
- Laminated glass provides an extra layer of security against intruders because it stays together even after it’s broken.
- Tempered glass tends to be cheaper than laminated glass.
- Laminated glass may be more energy efficient than tempered glass.
Is Laminated or Tempered Glass Stronger?
If it does break, laminated glass is easier and less risky to handle than tempered glass. Laminated glass will stick together even if it is completely punctured by something like a bullet, a rock or hail. Plus, if one side of the laminated glass is impacted, only that layer will crack. The sheet on the other side of the PVB will remain intact.
But tempered glass for skylights is considered to be stronger. It can withstand up to 24,000 psi of pressure, which is 4 to 5 times stronger than regular glass. The amount of pressure that laminated glass can withstand depends on the thickness of each sheet.
Both types of glass can develop cracks without breaking completely. If that happens, you might wonder if you can repair the damage without replacing the entire skylight.
The safest course of action is to replace the skylight. Cracks can lead to leaks and water damage, which can cost much more to repair than replacing a skylight. They also weaken the glass, making it more susceptible to breakage from storms and temperature changes.
You can fix a crack in a skylight temporarily by coating it with silicone caulk. You might also want to cover the area with plastic to prevent leaks. In some cases, you can extend the life of a laminated glass skylight by sealing the crack with a special type of resin. But you should contact an experienced skylight expert or roofer to remedy the issue so that it doesn’t cause problems down the road.
Which Type of Glass Should You Choose for Your Skylights?
Choosing between a laminated vs tempered glass skylight often depends on the building codes in your areas. If the skylight is large or high enough, it may be required to be made with laminated glazing.
However, if you have the option to select either type of glazing, the decision might be a tough one. If your skylight allows the sun’s rays to flow into the living area for most of the day, you might want to take advantage of the UV-blocking qualities of laminated glass. Laminated glazing is also ideal if you live in a noisy neighborhood. But if noise and sun aren’t an issue, you can save money by using tempered glass.
To get the best of both worlds, fill your skylights with tempered-over-laminated glass. This involves sandwiching the PVB layer between two sheets of tempered glass. It’s stronger than either tempered or laminated glass alone and won’t fall to the floor (or onto someone’s head) if it breaks.