With the Right Resources, Contract Glaziers Can Find New Opportunities in Point-Supported Glass

by Ellen Rogers

Transparency continues to be a huge design driver for architects, and the glass industry is responding with bigger and clearer spans of glass. Point-supported glazing also helps deliver a seamless, uninterrupted glass aesthetic. These systems aren’t new; in fact, their history dates back several decades. Despite hundreds of successful installations around the world, not every glazing contractor is prepared to, or even wants to, take on this type of work. Unlike traditional aluminum curtainwall systems where glass is supported on all sides, point-sup-ported systems are held at specific points on the glass. These applications require heavy engineering, careful planning and precise installation to ensure success.

“Point-supported fit-tings present unique challenges in designing the system to account for support of the glass itself, structural movement and coordination with surrounding materials,” says Ryan Kubr, team lead–senior glazing systems engineer for JEI Structural Engineering in Kansas City, Mo. “While structural movement and other interfacing usually can be accommodated with standard curtainwall components, doing so with a point-supported glazing system can be challenging due to the more rigid assemblies and fewer or no standard movement joints provided with most systems.”

Contract glaziers considering this type of work may have lots of questions and concerns about what to do and not do. “That massive cable-wall structure is impressive,” you might think, “but can I really do that?” Before jumping in both feet first, you’ll want to test the waters, perhaps starting with a small-scale installation. Fortunately, there are plenty of resources that can guide you along the way.

Understand What’s Involved

When comparing a point-supported glass system to traditional curtainwall, where the glass façade is supported on all four sides, one of the biggest differences is the need to (in most cases) drill holes in the glass for the attachment and installation of the anchoring system, such as spider fittings. As an alternative, Dow developed its Transparent Structural Silicone Adhesive (TSSA), which bonds directly onto the glass units, eliminating the need to drill through the glass.

“When it comes to point-supported glazing, there’s not really a standard product, but rather those that are custom to the actual application,” says Mike Nick-las, director of engineered glass systems with J.E. Berkowitz in Pedricktown, N.J. “It’s almost a free-form design of what the architect is envisioning and drawing. You may reuse the same fitting, but the glass makeup may change based on the application and design loads.”

He continues, “It seems like this area of the industry is less defined. You have a lot more conceptual drawings rather than fully defined drawings that you’re often bidding from.”

Jon Kimberlain, senior application specialist with Mid-land, Mich.-based Dow, explains that most of these facades are supported or connected around the majority of the perimeter.

“The point support is attached at the point of connection minimally, which is usually around 4 or 6 points,” he says. “Tolerance and placement become very important to enable construction of these facades with the reduction of contact points.”

Regardless of the method, understanding the composition of the glass, as well as compatibility with other components, such as sealants, is important. For example, Kimberlain says whether or not the glass is laminated can have an impact.

“Some laminates are sensitive to developing delamination along the edge, which is typically a result of plasticizer migration from the laminate,” he says. “Weatherseal contacting the edge of the glass is a perfect home for these plasticizers to migrate. It’s important to consider how the edge of glass is treated before the sealant is applied.”

“Selecting a laminate that’s not sensitive, or using some type of tape or impermeable backer material on top of the laminate to isolate the materials, are some ways to mitigate this,” he says.

He also points out that for certain adhesive systems used at the point of contact, the material has to be properly applied using heat and pressure.

“Heat kicks off the cure cycle of the material while the pressure removes the air at the interface of the adhesive, fittings and glass.”

Know Your Hardware

Hardware selection is another essential component.

“Understanding the limitations of the hardware being proposed via manufacturer recommendations and early coordination with a glazing engineer with experience designing point-supported systems can increase the chances of a successful on-time and on-budget project greatly,” says Kubr. “While there are many types of point-supported fittings available, minor differences between them, such as swivel fittings versus fixed fittings of the same style, can cause large changes in glass stress, deflection and final glazing thickness required.”

Nicklas suggests partnering with experienced suppliers that can offer guidance through the process.

“A lot of catalogs are available on the internet, but you need a knowledgeable resource or partner to guide you through the process to put [the system] together,” says Nicklas. “make sure it’s engineered correctly. Price can’t be just the driving force. It has to be an engineered product.”

Nicklas stresses that working with a fully engineered system is the key element, along with having it stamped by an engineer.

“People can buy hardware and glass, but they might not be putting the whole system together as an engineered system,” he says. “I do see more specifications requiring an engineer’s stamp on applications; our company doesn’t sell a point-supported application that’s not engineered.”

Architectural designs are becoming increasingly complex, and that brings a greater need to pay close attention to detail, to ensure nothing is overlooked or misunderstood.

“Point-supported glazing typically is limited by the allowable stress in the glass at fitting holes. While large insulating glass units are becoming more common in curtainwall applications, the use of such large glass panels in point-supported applications can quickly lead to over-stressed glazing if fittings are not properly placed,” says Kubr. “In addition to stress, deflection of the glass also can become a concern for both occupant comfort and structural integrity of fin-supported systems. Both stress and deflection limitations quickly can lead to thicker glazing and higher cost if not accounted for early in the design process.”

Nicklas agrees that the industry is vying for increasingly larger pieces of glass, but it’s also important to think about future costs, such as the potential need for replacement.

“It will cost a lot to replace that type of glass,” he says.

He also adds that the point-sup-ported process requires a detailed installation, which may need specialized equipment for lifting and handling, for example.

Keep Communication Open

“Projects always seem to flow more smoothly when the designers, glaziers and component manufacturers are involved early on,” says Kimberlain. “Because tolerances are critical, interaction between everyone can prevent misfits from happening in the field. These are relatively newer fabrication methods, so good communication prevents roadblocks or challenges more quickly.”

Nicklas adds, “Structural engineers, who are familiar with point-supported glass projects, are an integral part as well.” He stresses, though, the importance of working with an engineer familiar with this type of application. “Some [engineers] aren’t as familiar with point-supported glass as they are with curtainwall applications, for example.”

“Effective communication between the glazing contractor, the architectural design team and the glazing engineer can be critical to ensuring the selected system hardware allows the glazing and hardware to meet allowable stress limitations while also accounting for any structural movement around the system and other interfacing issues,” says Kubr. “Coordination of the glazing engineering with the architect early on in the project can help limit schedule delays and changes to hardware that can impact both aesthetics and project cost.”

Bottom line: for contract glaziers considering point-supported glazing work, remember to be detailed, specific and, if you don’t know, ask.

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