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
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
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.
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.
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
“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
“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.
Architects' Guide to Glass & Metal
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No reproduction of any type without expressed written permission.