Before designing a curtain wall system, there are five items to consider. They include: design criteria (wind loads, codes, etc.), structural criteria (live load and deflection), thermal considerations (CRF and U values), anchorage considerations and secondary water control.

Anchorages were a critical consideration in developing plans for Chicago's new waterfront Shakespeare Theater. The design of the 75,000-square foot, seven-story glass encased Shakespeare Theater, completed in 1999 as a final phase of an overall 1.1 million square-foot urban redevelopment of Chicago's Navy Pier, was to be reminiscent of a century-earlier Chicago side street. Chicago-based VOA Associates, looking to contain costs while sprinting from schematics to opening night in 15 months, chose an off-the shelf system, which despite being pre-fabricated, "was able to deliver many of the things we were looking to do," including a prism-like bay that permitted panoramic views of the waterfront, served to diffuse the impact of exterior sound, and reduced the visual impact of seven-inch-deep mullions, says Jim Spacek, VOA vice president and project manager.

Although not a contractual design-build project, the CM early on worked with a curtain wall manufacturer and an installer. "As a result," says Spacek, "we were able to consider proprietary issues earlier than normally would have been the case." Among the issues: at which floors the attachments would take place. "We ended up with a plan in which alternate floors carry wind and gravity loads and were able to plan for that in a way that minimized erection issues down the road," Spacek says.

"In this business, the water infiltration value is the thing that separates the men from the boys," says Scarborough. "The higher the resistance, the higher-performing the system, the more expensive the system is. On the vast majority of projects we do, we start at the upper end of the (resistance) range," he says. "We generally start a project looking at 12 pounds (per square inch), in some cases 15 pounds." Low-ratio systems offer water control at 1.77 and 6.24 pounds per square inch. At the upper end of the range are highly customized, high- performance curtain walls.

"At HKS," Scarborough says, "there are a half dozen of us who have spent our careers writing specifications. There are nine of us in the specifications group. We meet for a half-hour every morning. At lunch, we frequently have manufacturers come in and make presentations. We devoted September to discussions of waterproofing issues. We spent the month approaching the subject from an academic standpoint. Not every architect has that luxury, but you can't do this stuff casually."

"Architects, in general," he says, "tend to think of themselves knowing every-thing, as the master builders-those are the guys who get themselves in trouble."

"You have got to read-a lot," says HKS vice president Joe Sprague. "You have got to get together with the manufacturers. The thing I stress the most is that if the architect doesn't understand something-anything-find the manufacturer. Those guys will bend over backwards to accommodate us. Every product in our industry is becoming more sophisticated, more technical," says Sprague. "The weakness in the design industry in the U.S. is that there is not a formal mechanism to help the architect understand industries like curtain wall manufacture. This stuff is not taught in school. There are good architects out there, who have gone to good schools, but when it comes to the technical aspects of putting a project together, they fall down. The manufacturers know that, and they know that they possess the knowledge that will enable architects to do their jobs successfully. I spend time in plants. I call manufacturers.

They will fly in here to teach us how their systems perform. I say ‘I don't understand. Teach it to me.' They will."

"Ten years ago, it seems to me, manufacturers were more a part of the design process," says Dan Rogers, director of the curtain wall division for a Texas manufacturer. "Due to many fast-track projects, we have lost some of that interaction with architects, and we need to get it back."

"We've gone to great lengths to design and manufacture high-performance systems," says Rogers. "A lot has changed since Boston's John Hancock fiasco. There are a lot more products available and they are available now with zero sight lines, beveled, sloped or radiused exteriors, any color you want, any depth and profile." Architects are best served, however, Rogers says, by using those systems for the applications for which they were intended.

"You wouldn't put a residential window in a school," says Rogers. "If you did, it might last five years. An architectural window in the same environment might last 50 years." Systems are tested in the laboratory by subjecting them to 2,500 wind cycles.

Nearly all of what designers need to know to specify aluminum architectural framing systems is available at manufacturers' websites.