Volume 47, Issue 9 - September 2012


Does Glass Wear Out?
by Megan Headley

We all acknowledge that doors, windows and skylights have a natural lifespan. After all, on the American Architectural Manufacturers Association’s website, just before you click to download the information provided on Caring for Your Windows, Doors and Skylights, you will read this text: “Regular care and maintenance extends the lifespan and performance of windows, doors and skylights.” And on any given flat glass warranty you are likely to see a version of the following: This coated glass building product will not peel under normal handling and conditions for ten years from the date of manufacture.

In other words, glass products will someday require replacement due to expiration. Not the glass itself; you only have to glance at an image of the famous 700-year-old Rose Window glowing in Notre Dame to admit that raw glass can last, unless impacted by an external force (be it baseball or hurricane). It’s the components that beg for updates.

As industry experts become better at “enhancing” glass with miniscule layers of coatings, extra lites combined with sealants and spacers, and ever more artistic and complicated framing materials—materials that go above and beyond in protecting buildings from the elements—one wonders: are we sacrificing durability for superior short-term performance?

The Down Side of Enhancing “Eternal” Glass
We replace glass products when they break, and we replace glass products when efficiency has advanced so far that old needs can be better met by new technology. Yet when consumers replace glass products, are they thinking “failure” or are they thinking “expiration date?”

“Typically people replace their windows if they’ve got a leaky window or a draft, so it’s really looking at some of those signs of when it’s time to do a replacement product,” says Kevin Anez, director of marketing and product management for Viracon in Owatonna, Minn.

“I have been involved with many of these types of installations and I don’t recall being asked the question: ‘What is the life expectancy of this product?’” points out Joe Carlos, director of sales and marketing for TriView Glass in City of Industry, Calif. “Could it be that unless broken, it’s assumed that it will last forever?”

Is that necessarily a good thing?

“I like [the] idea of putting an ‘expiration date’ on various products,” muses Charles Clift, PE, F. ASCE. Certainly the president and senior principal of Curtain Wall Design & Consulting (CDC) in Dallas has seen his share of window failures. Still, Clift is the first to point out, “Material stability of primary sheet glass is fairly inert in most environments. After all, glass is inorganic.”

In other words, if glass is going to fail, it’s because of “debris impact, thermal stress, latent defects (edge damage or nickel sulfide inclusions), improper installation or improper design.” In other words: something has gone wrong. Old age? Not so much.

But considering in its long history, glass has only in recent terms become the playing ground of increasingly more complicated coatings, experiments in efficiency on a nano level.

“The coating isn’t going to wear out,” says Barry Corden, senior director of product applications for Guardian Industries in Auburn Hills, Mich. As he explains it, “There are layers of silvers in our more modern coatings; the older coatings without silver are actually more durable, but the ones with silver also have layers that protect that silver layer. Anything like UV or visible light that passes through does not degrade that inorganic material.”

Historically, though, trial and error in this new frontier has led to what might now be called “instructive” breakdowns. “Some reflective coatings in insulating glass units (IGU) in the 1970s began to oxidize over time and looked unsightly after 10 or 20 years,” Clift recalls. “Painted coatings on glass have had issues with adhesion/corrosion, usually within a few years of manufacture. Films on glass have also had issues with adhesion/corrosion, also within a few years of manufacturing. These issues are not structural in nature, so the stability of the wall is not in jeopardy, but these issues can become significant enough to influence performance with respect to aesthetics, transparency, heat gain, etc. While the advancement of coated architectural flat glass has been remarkable, there still remains some risk of durability over time, since new materials and new applications, technologies and assemblies do not have a mature track record of successful history.”

Today, most glass professionals will tell their customers that if a coating is going to fail, it’s because it’s been impacted in some way, with moisture being a key culprit. More likely, if a glass coating needs to be replaced it’s because better technology has arrived. Coating performance doesn’t fail; it’s surpassed.

More likely, if a glass product has failed, it’s because another component has reached its end.

Technology Improves Faster Than It Fails
“It’s not that the glass itself ever becomes ‘bad,’ or doesn’t do its purpose anymore. The glass will be there—it’s just what you want out of it,” says Urmilla Sowell, technical director for the Glass Association of North America. Sowell adds that coatings have staying power because they’re generally protected within an IGU. “Every now and then you have compatibility issues with the coatings, as to your sealant or moisture or interlayer or something like that, but if you leave the coatings alone they’re fine. It’s more about finding a different performance level now,” she says. “It’s all about the performance.”

And changes are coming rapidly to find new ways to improve performance. “Right now, the energy codes and standards are really affecting the types of glass we use,” says Craig Carson, vice president of the glazing contractor A1 Glass Inc. in Englewood, Colo. “We’re seeing different glass types now that even two, three years ago we didn’t see. For years, an IGU was just two lites of glass with an airspace and different coatings—now we’re seeing coatings being applied on the number-four surface to try to get it to perform to the level of triple glazing. I see the manufacturers are trying to come up with different glass types to use there.”

Mike Nicklas, business development manager for J.E. Berkowitz in Pedricktown, N.J., agrees that energy codes are transforming the type of products appearing on the marketplace. “As a result, people are spending the money to have a better performing window. Therefore, you’re probably seeing more longevity out of it.”

You’re also likely to see some experimentation in reaching target efficiency numbers. According to Carson, a recent occurrence among new coatings is that “the pyrolitic on the number-four surface, instead of being a smooth, glass-type finish, is ‘grabby,’ almost abrasive, and the manufacturers are trying to eliminate that. They tell you [it’s] to perform better, but it’s to smooth the glass so that it’s a smoother surface to clean.”

Because experimentation is still rife in finding the magic combination that will boost energy performance another fraction further, it’s nearly impossible to pinpoint a coating’s “life expectancy.” Products are evolving too rapidly.

However, plenty of factors go into ensuring that window products meet the only lifespan that most building owners will pay attention to: the warranty. Those factors, per Nicklas, include “testing, weatherization testing, experience—and industry pressure.”

“The standard in the industry is a 10-year warranty,” Anez points out. “The primary target is to make sure that the glass product can hit its warranty date with no issues.

Extending the warranty beyond that agreed-upon timeline poses challenges. “If you warrant a product to perform for 50 years, what does that mean if it fails in year 49? Year 51? Does it require maintenance to perform that long and was it properly serviced?” points out Jon Kimberlain, application specialist, high performance building solutions, with Dow Corning based in Midland, Mich.

“Really, I think there’s an expectation beyond that that the glass is going to last for several decades,” Anez adds.

The Better Windows, the Harder They Fail
Most professionals agree that when coating failure comes, it’s the result of another component’s end of life.

“It’s really the silicone or sealant material where degradation tends to occur,” Corden says, noting it’s a failure that wreaks havoc on glass and its coatings. “As far as longevity, the only source of failure (other than someone breaking the window) that is common is damage because there’s water penetration into the IGU,” Corden says.

Yes, Clift agrees, “The majority of renovations are limited to replacement of sealant and gaskets, whereas the original glass remains to continue its function.”

On the other hand, Kimberlain says, “We know that projects glazed with silicones in the late ’50s and ’60s are still functioning as a weatherseal and that the first four-sided silicone structural glazing project still is performing since 1971.” Kimberlain goes on to add, “Our knowledge of durability is based heavily on two things: empirical evidence of performance and knowledge of our material to help define design constraints, whether it is chemically or physically. I think comparing how a mechanical hinge wears versus a sealant is two completely different processes. From my standpoint, I would expect the sealant to wear because it is a dynamic environment, but I am not sure how I would describe a sealant ‘wearing’ out relative to a metal hinge rusting. I know there is a potential for silicone sealants, if applied properly, to perform for a very long time.”

CDC pegs service life for typical commercial buildings at 50 years, at least when it comes to structural design criteria. “That has become a sort of de facto value for durability of wall designs,” as it relates to structural concerns, Clift says, referencing ANSI A58 and ASCE 7. He adds, “Base materials such as steel, aluminum and glass are fine for structural stability for at least 50 years, since they function generally in a static state.

“Glass in windows is designed to minimum stress within expected windloads for 50- to 100-year events,” Kimberlain adds. “Glass performance is relatively well understood and predictable for design purposes as it has been used for more than a hundred years in modern building practices. So you have a predictable material you can design to minimize stress and strain, and you also have a material that has inherent resistance to UV degradation because of chemical make-up (and silicones for that matter).”

Sealants are another matter. As Clift notes, “Operable windows and doors do not seem to survive for that length of time without serious maintenance. High-performance gaskets, sealants and finishes exposed to the weather are expected to last 20 years. However, warranties range from two to 20 years, depending on the manufacturer. Environmental conditions can alter material life, such as areas with high levels of acid rain that will show accelerated corrosion compared to a dry or mild climate area.” In other words, the more complicated glass products get, the more can possibly go wrong.

Jason Funk, president of Western Window Systems in Phoenix, agrees that it’s the individual components that make up a window—and how they interact with one another—that determine a lifespan.

“If [components] are expanding and contracting at different rates, that can obviously impact things over a lifespan, and then add in extreme heat or cold … Those things can affect the lifespan of the individual parts. For example, for an aluminum window (which is mostly what we do), the aluminum itself is going to be there, it’s not going to go away. But if you have operators or hinges, things like that that may have a lifespan after being used, opened or closed so many times,” Funk says.

Anez adds that it is critical to look at windows as a system, “because it is a system that is made up of sealants and framing materials and glass that all become components of an overall building system.”

Admittedly, IG systems in particular have always been under a microscope for failure.

“When double-pane windows came out, there were a number of issues in the field … ” Corden says. “ … If they’re made correctly today, if the workmanship is good, and because, especially in commercial buildings, these are all mechanized fabrication operations, they come with a warranty.”

“Various seals and coatings over the past several decades have had performance and durability issues. Consequently, warranties for IGU are typically in the two- to ten-year range,” Clift says. “If you’ve ever had a ‘fogged’ window, that is probably an edge seal failure and fixing it requires replacement of the IGU.”

Yes, windows are a complicated assembly of a number of material types that must work together in harmony. Most of them do so for a significant period of time, as studies show. In 2010, the Insulating Glass Manufacturers Alliance (IGMA) completed its 25-year field study of the correlation of actual in-service IGU failures to the ASTM E 773 Standard Test Method for Accelerated Weathering of Sealed Insulating Glass Units and ASTM E 774 Standard Specification for the Classification of the Durability of Sealed Insulating Glass Units for classes C, minimum performance; CB, moderate/mid-level performance; and CBA, maximum performance (see September 2010 USGlass, page 76). According to Margaret Webb, executive director of IGMA, 80 percent of the buildings had no IG failures after 25 years.

As triple-glazing becomes more popular as a result of increasingly stringent performance expectations, installers and fabricators might find themselves wondering how much experimentation is going into the durability of these new units.

“For many applications, we still don’t want to use triple glazing because it doubles your chance of the seal failing, because you have two airspaces versus one, even though that’s a very low denominator,” Carson says.

On the other hand, Nicklas points out, “I think the technology is much greater today and there’s more technology being put into windows to make them last even longer—provided the installation is done correctly. We see IGUs that are typically warranted for ten years, but last for 20 years or more—provided the installation is done correctly, and water or moisture or other factors are not affecting the unit.”

Kimberlain likewise stresses the importance of proper installation. “Poor application or application requirements can negatively impact the life of a sealant. Misapplying or asking silicones to perform near their failure point will limit the lifespan. Not understanding the impact of the environment can influence [lifespan as well], because I would expect a structural glazed interior glass partition to be subjected to much less stress than an exterior glass curtainwall in Alaska or Las Vegas. So it is incumbent upon us to continue to develop the tools and knowledge of how our materials (and others, like glass and metal frames) work within a glazing system and the environment.”

Kimberlain adds that new technology outside the system also is swaying our idea of glass products’ lifespan. “I am excited by the use of new modeling tools and software that are better able to predict how materials react such as finite element analysis,” he says. “We may never know the exact time of failure, but we have more insight on how to preserve the performance of the material to maintain materials that we perceive to be highly durable.”

Changing Failure to Opportunity
So how does the glass industry help home or building owners come to realize that their windows will wear out? That failure isn’t a problem with the window’s manufacture but an expected part of the product’s life? That a window is, just like a roof, an air-conditioner or a water heater, a part of a building that should be targeted for replacement after decades of successful performance? How do we change the focus from failure to success?

“As a consumer I agree everything should last forever,” Corden says, quickly adding, “but of course, from a glass industry point of view, nothing is forever.”

That’s what warranties and product care brochures are intended to help customers realize.

“During the design process, engineering, fabrication, installation and maintenance should be reconciled with expectations,” Carlos says. “A warranty can then be issued and it becomes reasonable to expect the glass to last a very long time. Education and communication are the key.”

Part of the lifespan question may be addressed by future studies of glass, after installation. Sowell explains that current life cycle analysis studies are focusing on the environmental impact of production; this “cradle-to-gate” focus quantifies and interprets the actions that take window components from their initial manufacture to installation. Future studies might look beyond installation. “Gate-to-grave analysis covers installation to replacement,” Sowell says, adding that the latter cycle is expected to address such as questions as: “If the building is demolished, what happens to that window? Does it go to a landfill? Does it go into roads or countertops? What happens afterwards?” She adds, “The ‘to grave’ [portion] is a huge unknown right now.”

With broken glass so much in the news of late, more industry professionals have expressed a desire for glass product success stories.

“By now, there is a lot of work out there that can be evaluated. It would be interesting to look at some projects and see how they held up to time and if they, ultimately, met expectations,” Carlos says.

“Will it last forever?” Nicklas asks of these glass products. “I think a commercial building owner recognizes that things don’t last forever, so there is a recognized obsolescence at a certain point. What that business owner’s horizon expectation is, I think, is dependant on what their horizon of ownership is. Institutional buyers tend to look long-term. Investment buyers look short-term.”

Even though recent trends show more building owners looking for high quality and long-term sustainability in their new construction projects, who’s to say who will be replacing those windows by the time the first component expires?

Funk points out that lifespan is rarely discussed, “because the lifespan of the product tends to be longer than what a typical home [or building] owner will stay in the building. It tends to not come up.”

While educating building owners about the regular glass replacement cycle, it can be expected that all building owners have differing ideas of what constitutes failure (much like they may have differing ideas of what constitutes a maintenance schedule).

“I think that each building owner or homeowner has a different level of risk they’re willing to take,” points out Alissa Schmidt, architectural design manager for Viracon. “Some people are replacing their items on a regular maintenance basis whether or not they have any issue; other people are willing to take more risk and wait until it’s basically completely broken or it can’t be fixed anymore. In commercial construction there’s a whole wide range of building owners and their acceptance of how much is failure and when it is really broken.”

Of course, the best performing units of 20 years ago may already have been replaced by a more aesthetic option.

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