Four Seasons of Sun: Glass vs. Lexan

As summer enters its last throes, the days are getting shorter and the nights a bit more chilly. Here at Brady-Built Sunrooms, we continue our work to bring the best and highest quality sunrooms to you. We have a series of articles written by Registered Architect, Robert Wironen, whose knowledge and experience will help guide you through some of the complexities faced when choosing a sunroom. We hope you enjoy these articles and gain helpful information.

The first article addressing the choice of Lexan and Glass in your sunroom. While both have their advantages and disadvantages, Bob breaks down why some manufacturers do not measure up to the quality of Brady-Built's Split Silver Titanium Glass.

Polycarbonate which is commonly known by GE’s brand name, Lexan is an extremely tough plastic that has been used in many applications from helmets to car headlights to bullet proof glazing to eyeglass lenses. The characteristics that make it so well suited for the applications I mentioned are also one of its weaknesses.

Lexan is a polymer that is extremely flexible with very strong molecular bonds. These qualities make it virtually impossible to break, but also make it very soft. The soft surface is very susceptible to scratching. In applications like helmets, minor surface scratching don’t matter.

For headlights, the surface scratching is more of an issue and in glazing and eyeglass applications it is a serious concern. Other issues with Lexan as a glazing material are yellowing due to UV exposure and sag.

The industry responded to the concerns raised by scratching and yellowing by developing special coatings. The most commonly used hardcoat and UV absorber for polycarbonate today is a combination of Alkoxysilane and Colloidal Silica. They form an extremely thin film on the polycarbonate that is chemically similar to glass.

The problem with this coating is that it is only a few microns thick and is bonded to a material (Lexan) that has a vastly different coefficient of expansion. The combination of thermal cycling and the thinness of the hardcoat cause it to delaminate over time. The delamination is at a microscopic level, so it won’t be obvious (big sheets peeling off), but will manifest itself in visual crazing and poor optical quality.

The thinness of the coating also makes it highly susceptible to damage by abrasion. Small particles that are deposited on the surface by rain and wind will damage the surface over time, but the damage is exacerbated by attempts to clean it. Rubbing of the grit covered hardcoat surface with a cleaning cloth will wear the surface coating off.  

Glass is an extremely hard material. In fact, except for diamonds and other precious gems, and carbides, there are very few materials that are harder. This makes it very resistant to scratching. It also makes it easy to break. To a limited extent the weakness of Lexan is the strength of glass and vise-versa.

To make glass stronger for use in applications where an impact is possible or where breakage could cause harm, the glass industry developed tempered glass. Tempering the glass makes it very resistant to breakage and makes it so that when it does break, the pieces are very small and much less likely to cause serious harm to a person. Because glass is uniformly hard throughout, it is not subject to abrasion damage the way polycarbonate is. The glass on a Brady-Built sunroom is tempered.

One concern that has become more important to consumers especially in the past few years is energy conservation. Glazing systems have been developed to reduce energy loss through windows and sunroom walls.The greatest challenge has been to make a glazing system that will allow as much energy (sunlight) into the house in winter as possible, while preventing energy (your heating system) from escaping through the glass. This part of the problem has been solved by the development of low e coatings and argon filled double glazing. The difficult part is to ask the same glazing system to do the exact opposite in the summer; keep the suns energy outside and letting any heat that has built up in the house out as well. This part of the problem has not been solved and must be addressed by other means.

It is impossible to have a glazing system that allows the maximum energy into the house in the winter and prevents heat build-up in the summer. Any claims that there is a glass or other glazing system that “does it all” is patently false. Other means are required.

To understand why the glazing systems respond the way they do in summer versus winter, it’s important to know one fundamental element of heating and cooling design.  The amount of energy needed to make a room comfortable is directly proportional to the difference in outdoor temperature versus indoor temperature.

For instance, if you want your house to be 70 degrees on a 10 degree day in January you need enough energy to raise the temperature 60 degrees.  If you want your house to be 70 degrees on a very hot day in the summer, let’s say it is 100 degrees outdoors, you will need only half as much energy to get it to your target temperature of 70 degrees.  This is pretty obvious when you read it, but it has important implications when selecting glass for a sunroom.

Using heavily tinted glass or plastic will help prevent the sun from hitting surfaces in the room, reducing the amount of heat generated in the room, but a significant portion of the sunlight is converted directly into heat energy in the tinted glass.

About half of this heat energy radiates into the sunroom causing the temperatures within the room to rise to levels well above the outdoor temperature.  Though this is a relatively small amount of heat, remember, as I mentioned in the previous paragraph, that much less energy is needed in summer to make a big difference in comfort (or discomfort in this case).

We use special Split Silver Titanium Glass in all our sunrooms. Our coating and tinting formulas are optimized for the harsh New England climate so they perform well under a variety of weather conditions and temperatures while maintaining optimum insulating properties all year round.

Split Silver Titanium Glass is incredible stuff – it uses eleven different materials that are applied to the glass by a metal vapor deposition process, providing superior energy-efficiency and comfort during all seasons.

But what really sets us apart from the competition is our proprietary glazing system utilizing a structural silicone to more-efficiently seal the glass to the sunroom’s exterior for simply outstanding reliability and longevity. Unlike the rubber seals used by the competition, our silicone seal stays flexible for years and is unaffected by UV rays.

What does this mean to you?  You don’t have to worry about rainwater leaking into your sunroom or  cloudy glass caused by poorly sealed glass.  That means you’ll be able to enjoy crystal clear views from your Brady-Built sunroom for many, many years.

Do you have a unique glass request or requirement? We offer a wide range of high-quality, two-pane insulated glass from Guardian Industries, the world’s largest glass manufacturer, finished with our proprietary glazing system.  In fact, we work with virtually every major glass manufacturer, so if you have a preference for the glass used in your sunroom, we’d be happy to get it for you.

Whether you choose high-performance Split Silver Titanium or superior insulated glass, you’re assured peace-of-mind with a Brady-Built sunroom, crafted from the finest materials available.