Volume 28, Issue 4 - July/August 2014

Structural Movement
As Architectural Designs Evolve, Structural Glazing Follows
by Ellen Rogers

Glass is getting thinner, bigger and clearer. It twists, it curves, it morphs into unique geometric shapes. Without question, architectural facades are very different today than they were 30, 20 even 10 years ago. As technology has evolved, architectural designs have become increasingly cutting edge. But reality check: those thin, big, curvy walls aren’t for every project—nor does every project have the budget necessary to use them. Structural glazing, however, still provides plenty of opportunities to design and construct a unique façade—and the possibilities to do so continue to evolve.

Techniques such as two- and four-sided structural silicone glazing (SSG), for example, have been around for decades—and continue to draw a strong interest from architects. According to Joe Marks, chief strategy officer with Architectural Glass & Aluminum in Livermore, Calif., SSG projects are even more popular now in some ways when compared to years past.

“It’s a mature practice,” he says. “[SSG] may not be a novelty, but it’s a part of their [architects] pallet.” He says he’s seen a shift toward designing the external component of curtainwall as a design feature rather than just a necessary part of the glazing system. “A SSG curtainwall becomes the canvas and the external expressed components are the design feature,” he explains. “Architects are not moving away; they are embracing it even more.”

Product Differences

Still, facades today are different than those of 30 years ago. Marks says some things to consider when looking at the changes in façade designs are the increase in both the complexity of the project and the size of the glass panels.

“The typical glass size [early on] was around 35 square feet. Now it’s not unusual to see glass that’s 50 square feet and above which increases the load requirements of the silicone,” says Marks. “The larger the glass the more silicone you need and the architect needs to understand there is a relationship to the site line of the silicone joint and those larger spans of glass.” He adds that suppliers are stepping up their products to accommodate the increasing loads to accommodate larger lites.

Larry Carbary, an industry scientist with Dow Corning based in Midland, Mich., says there’s a shift in that products today are more robust when compared to years past. Products are being designed for higher windloads; there are also more silicone gaskets and more unitized shop applications compared to stick systems. And, he stresses, there’s a greater appreciation of the quality control process.

“You have a lot more attention paid to quality control,” says Carbary. “Within the specifications they are taking serious what has to be specified of the installation contractors.”

Speaking of the system’s performance, Carbary adds that when the sealant is placed around all four sides, it provides a thermal, air and water barrier and allows movement in glass and aluminum. “We’ve seen very few callbacks related to air, water and structural performance,” says Carbary.

While structural glazing may have started with silicone, today there are other options available for achieving a similar two- or four-sided aesthetic. 3M, for example, offers acrylic foam tapes, which can also be used in structural glazing applications. According to Steve Austin, global technical service specialist, 3M™ VHB™ Tapes - Architectural Markets, the structural glazing tape essentially replaces structural silicone to attach the glass panel.

“Structural glazing goes back to 1990 for 3M,” says Austin. “It seems relatively new to some people in the U.S., but we have been doing this for 24 years now. Our first structural glazing project in the U.S. was in 2006.”

L.A. Confidential

While structural silicone glazing has continued to thrive, it is not universally accepted. Joe Marks, chief strategy officer with Architectural Glass & Aluminum in Livermore, Calif., says, for example, Los Angeles County is adverse to it.

“There’s a high concern for public safety and in the case of L.A. if you go back to the 1980s there have been incidences of building failure in one form or another (not related to SSG) that were very public and there was a lot of public scrutiny,” he says. “As a result, the county became very conservative.”

He’s quick to point out there has been no direct evidence of a specific problem or high probability of SSG failure, “it’s just to them there’s still this [perspective] that it’s a newer technology, when in fact it’s been around since the 1970s—that’s four decades or more in the field without full-scale failure.”

He says it’s not that SSG projects or even others such as point-supported glass walls have not been built in Los Angeles. “They have had variances … but it requires a lot of due diligence, test reports, etc. [The county] wants a lab research report, etc. for all components that go into the application, so you have to be extremely diligent to make sure everything going into the building has met approval through the building department.”

No Room for Failures

What precautions should be taken to ensure a safe and sound application?

Joe Marks, chief strategy officer with Architectural Glass & Aluminum in Livermore, Calif., explains two likely causes for a failure. “One could be inadequate design of the size of the SSG joint, another could be the sealant’s incompatibility with materials being adhered,” he says. “The other might be a contaminate, whether onsite or in shop, that prevented the adhesion.”

And the fix for such a failure doesn’t come easy.

“It can be elaborate if there’s a failure throughout the building or one that is characteristic of the project. Even, if it’s a small aspect of the project, it will still be enough to raise red flags so that the entire installation is suspect,” says Marks. “The remedy is extensive and that means cutting the glass out completely, cleaning and starting over on both the glass and metal substrate to which you’re adhering. It’s very involved and very expensive.”

Suppliers, however, also take extreme cautions and measures to ensure a quality procedure. Steve Austin, global technical service specialist, 3M™ VHB™ Tapes - Architectural Markets, says his company takes precautions to control who uses the product and for what projects and restricts the sale of its tapes to only approved applications.

“We have a strict approval process,” he explains. This includes a review of drawings/design criteria. “We explain this to the customer and then they send in the substrates for adhesion testing … we can’t predict adhesion; you just have to do the test, which only takes three days for acrylic foam tapes,” says Austin. “We then issue a test report to the customer that explains the results, etc.” He adds that before the contract glazier begins the project they also undergo training with a 3M representative, who issues a standard operating procedure as a step-by-step guide; this is followed with production audits to make sure the operators who are working on it are the ones who were trained, etc. A warranty can be issued upon completion.

Structural silicone suppliers follow similar procedures as well. Larry Carbary, an industry scientist with Midland, Mich.-based Dow Corning, says his company asks specifiers to include in their contract documents to the contract glaziers submissions from the structural silicone supplier that include the following criteria:

• Product data sheets;
• Blueprint review of the project so that the design can be confirmed as meeting industry and project requirements;
• Adhesion test reports on actual surfaces that come in contact with the structural silicone;
• Compatibility test report on accessory materials that come in contact with the structural silicone; and
• Application and quality control instructions for the use of structural silicone.

“Dow Corning will then provide the services that allow the contract glazier to fulfill his contractual obligations,” says Carbary, explaining that his company offers the application and quality control training, blueprint review service, adhesion testing and compatibility testing. 

“Communication of these reviews and results will include application and quality control instructions. If the contract glazier is unclear of any of this or is uncomfortable in any way, Dow Corning will provide training on the application and quality control of structural silicone in person. Knowledgeable service and support is critical to ensuring installers are comfortable installing and quality controlling structural silicone applications.”

Questions, Concerns

Still, the applications are not without questions and even concern, in some cases. Marks says something he has faced in working with architects is a conflict of design intent verses what can actually be done cost effectively.

“The architect might want a large opening module done with one 75-square-foot insulating glass unit. You have to look at how it will perform from a loading perspective, how it pencils out from a cost perspective, find a fabricator who can effectively make units that large, etc. … it’s not always the most practical,” he explains. “While architects may be pushing the envelope, there are often constraints that bring them back down a little bit. They have a vision, but sometimes there’s the reality of what can be done.”

Carbary adds it’s also important to keep in mind attention to detail and quality control.

“One of my worries is the younger professional will take [this] for granted. I hope quality control never becomes lax. I remember 30 years ago people were afraid of [SSG]; it was a fear factor and today nearly every major iconic high rise is specified with SSG.”

“It comes down to managing risk,” agrees Austin. “The industry can’t afford to have a failure; no one wants panels falling off a building.”

Looking Good

But how do these projects hold up and what do these buildings look like after 30-plus years? They still look good, experts agree. Marks points out that’s a testimony to the industry.

Carbary points out that the first four-sided SSG project was the SHG Inc. building built in 1971 in Detroit. He says it has held up well and is still performing today.

Marks agrees, “If you look at the amount of SSG square footage installed it’s remarkable. The performance has been very good and it’s a resilient product. If it’s cleaned and maintained properly it will look as good [decades later] as it did when it was installed.”

What’s Next?

Structural glazing applications have become well established in many markets. But what’s next? As architects continue to search for the next big thing in facades, where will structural glazing applications fit in? Marks says he sees a challenge to keep designs cutting edge mixed with increasing code restrictions/parameters related to building loads and energy performance.

“… I think eventually we’ll see double cavity IG and [triple glazing] becoming common to get thermal requirements down to where architects can continue to design with glass [given increasingly] stringent energy code restrictions,” says Marks.

Carbary adds, “The use for SSG is stronger than ever because of its proven performance with each passing natural event such as hurricanes, earthquakes, rain events, extreme temperatures and UV exposure. Structural silicone is the key to performance for seismic-, impact-resistance and blast mitigation. The continuous flexible rubber anchor allows the glazing to remain in the opening after the event. This is critical for human safety during these events.”

Speaking of structural glazing tapes, Austin says he’s also seen increasing opportunities for applications in which the products can be used. For example, he says his company’s products have grown to be used in hybrid stick-wall, storefront and skylight/canopy applications when early on they were most commonly used in unitized and door/window applications.

“The industry has evolved and has seen the value in its use in hybrid-stick wall systems,” he says, explaining these jobs are still a stick wall system, but the glass is bonded to the frame in the shop and then sent to the job site and installed with mechanical fasteners that lock the frame into place.

Austin adds that these tapes have also provided new opportunities for contract glaziers who might not otherwise take on a structural glazing project.

“Glass shops can do these four-sided jobs where they might not have entered the market before. Because acrylic foam structural glazing tapes are fully cured, the units can be moved immediately after bonding. This allows glaziers to do these types of jobs as they don’t need expensive silicone dispensing equipment nor large shop space for curing glazed units.”

Looking at the growth and possibilities that surround the future of structural glazing, Carbary says, “There is always interest in newer developments, but nobody wants to be first. Our industry really resists new technologies.” He points out that even after 40-plus years there are still some design professionals who think of it as “so new and unproven that they refuse to acknowledge the history. There was actually one design professional who publicly declared that structural silicone was ‘Krazy Glue’ and refused to consider it.”

The challenge for the industry will be to continue to educate and inform architects and others the benefits that these products can provide—design flexibility and design freedom. And its performance is proven. AGG

Ellen Rogers is the editor of the Architects’ Guide to Glass & Metal magazine. She can be reached at or follow her on Twitter @AGGmagazine and like AGG magazine on Facebook to receive updates.

Architects' Guide to Glass & Metal
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