Volume 46, Issue 7 - August 2011

Architects Guide To Glass
Special Section




Balancing Act
Combining Structural and Thermal Performance in Today’s Architecture
by Ellen Rogers

Increasingly large spans of glass are a popular design feature; yet codes are demanding increasingly stringent energy performance. If glass has historically been thought of as one of the weakest elements in terms of heat loss, how can the architectural community balance these two trends? Changing technologies and product development are helping to achieve both the desired aesthetic as well as the mandated performance features.

Necessary Steps
Architects agree, there is a need for balance when it comes to structural and energy performance. Keith Boswell, an architect with Skidmore Owings and Merrill, says his firm does a lot of work with large sizes of glass; Boswell says he usually considers “large” as more than 9 feet tall or wide and 84 square feet in area.

“The performance issues must be balanced. By that, each is equally important, but you have to start with one as primary and then balance the other performance requirements. I usually start with structural and if it doesn’t work structurally then you have a non-starter,” says Boswell. “The energy performance is equally important, but most often in our work it is selecting a type of glass, glass assembly or combination of glass with other components to achieve the thermal, light transmittance and solar performance values necessary.”

According to Ben Tranel, an architect with Gensler, there are several steps to take to help ensure the project will provide the necessary thermal and structural performance.

“We evaluate the structural and thermal performance with software, but it is also important to discuss with manufacturers and conduct appropriate performance testing for a project,” explains Tranel. “There are usually some detailed technical issues that cannot always be predicted and testing is one of the best ways to thoroughly vet a product before its use.”

Al Stankus, general manager for Technoform Glass Insulation North America, says it’s important to understand how all components in the fenestration system must interact to define the criteria of a high-performance system.

“You have to look at a variety of technologies and design components as it’s not just about a single performance characteristic,” he says. “I?believe system designers are feeling the pressure to bring high-performance into the design earlier on due to code changes, etc.,” Stankus adds.

Patrick Muessig, vice president of global technical operations with Azon USA, adds, “The framing in aluminum fenestration products is often the weakest link so large spans of the correct type of glass are often a way to improve the actual thermal performance of a building. In doing so you have to make sure the framing system installed is designed to withstand both the load of the glazing and the structural/wind.”

Don McCann, manager of architectural design with Viracon, says his company often suggests making the glass thicker, which helps provide structural support. Another added benefit, he notes, is that thicker glass also makes it appear flatter.

Growing Awareness
While companies and organizations within the glass and fenestration industry have taken steps to educate the architectural community about structural and thermal performance, many agree there is still work to be done. Stankus says the answer to the question, “how do I balance the need for thermal performance in large window designs?” is in component selection, understanding the technology, and also the strengths and weaknesses of the system.

According to Muessig, product ratings and codes also need to go beyond a product’s performance in a test lab at a standard size.

“There is a need for evolution toward a real project size rating to long-term energy performance and finally Life Cycle Analysis, which includes recycled content and recyclability of the materials within the fenestration unit,” he says.

Challenges
As both architects and those in the glazing industry continue to work toward building more efficient structures, there are a number of challenges and design considerations. Muessig says one challenge will be balancing energy efficiency with structural performance with what the economy will allow.

“There are solutions out there now for an R-5 architectural window and beyond, but trying to achieve it in a practical manner that can become a product on an everyday project needs more time to evolve,” he says.

Mark Silverberg, president of Technoform North America, adds, “The challenge is quantifying and communicating long-term energy savings and the potential value created in sustainable architecture [through the use of] commercially available technology … whether it’s a retrofit or new construction.”

McCann says another challenge is finding a balance point between the amount of natural light coming in while still achieving the architect’s desired aesthetic. He explains while there is a desire for more natural light and daylighgting, this may lead to glare issues and occupant discomfort. As a result those inside the building may close the blinds, which then takes away from the view/aesthetics. Closing the blinds might also lead to turning on the lights, which adds heat, leading to the air conditioning coming on.

“It’s a vicious cycle,” McCann says.

Boswell says achieving balance is always a challenge.

“Owners and architects consistently want large areas and expanses of glass. In some climates, building uses, orientations, functions, etc. these two and often competing interests can be accomplished. In [others] they are, frankly, not compatible but we consistently [try and] force the issue.”

So in order to continue toward this vision, it’s important for the architectural community and the glass industry to continue working together.

“We’re all well aware of the economy and the accelerating pace of change in product and system development,” Stankus says. “As a result, manufacturers are developing consultative relationships with architects to increase the understanding of the impact these commercially available technologies can have on high-performance system efficiency.”

A New View
As demands for energy efficiency continue to increase, codes and building requirements will also continue to evolve. And along those lines, glazing products will likewise continue providing the architectural community a range of high-performance solutions.

Ellen Rogers is the editor of the Architects’ Guide to Glass & Metal magazine.


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