Trompe l’Oeil to Go
Perkins+Will’s Toronto office found that for its Engineering V building at the University of Waterloo in Ontario, Canada, the kind of repetition that would have been fatal at Toren made perfect sense. The trick was making the grid interesting. Andrew Frontini, the Perkins+Will Toronto office principal who was the lead designer on the project, turned to white ceramic frit to give the building’s elevation a three-dimensional appearance and to conceal the striped effect common to curtainwall-clad offices.
The coating is silk-screened onto the vision and spandrel glass in dot patterns of three different densities, arranged to create the illusion that the building’s exterior is studded with shallow pyramids. The lightest in appearance is a 75 percent dot pattern; medium is 35 percent; and the most transparent portion of the vision glass is 5 percent. “It’s really a tromp l’oeil,” he says. During the day, areas of vision glass, which have the least amount of frit, appear to be dark. But, as twilight comes, the frit is backlit in rooms where lights are on, gradually revealing those interior spaces.
Applying frit to glass can be expensive, Frontini says. “But if you minimize the number of printing screens, you can do a fritted job at a very modest cost premium.” In this case, limiting the number of screens to three helped, but the expense was further offset by efficiencies in prefabrication of the curtainwall system. The fabricator insisted on extremely large unitized panels completely assembled at the factory.
Each of the unitized panels spans from floor to floor and roughly measures 14 feet tall by 9 feet 8 inches wide. The large unitized panel is made up of two smaller units of insulated vision glass and two smaller units of insulated spandrel glass. Three panels installed side by side cover one column bay. “We were really at the limits of what the manufacturer could do in terms of size,” Frontini says. Preassembling the large panels and then trucking them to the site allowed for faster installation (and therefore less on-site labor); better quality control, with fewer dimensional adjustments in the field; and the ability to work indoors—a plus in the Canadian climate. “Once they started installing them, the building was enclosed very quickly,” Frontini says.
From the exterior of the building, several 10-inch-high horizontal strips can be seen dividing the façade. Each houses a 4-inch-diameter, cylinder-shaped vent that occupants can rotate by hand to allow fresh air into the building. These are located at the top of each windowsill. The vents are a standard detail developed by the curtainwall manufacturer and installed into the unitized panel during fabrication. They even come with built-in insect screens.
Frontini says that his quantity surveyor’s cost estimate for the curtainwall, which was fabricated locally, came in at CAD $65 per square foot. He believes that, because fabricators are not as busy in the current economic climate, the cost would likely be even less today.
Behind the Polycarbonate Curtain
The Land Port of Entry at Massena, N.Y., is a gateway for trucks and automobiles coming in from Canada. Like all government buildings, port of entry facilities must meet extremely high safety and security standards, while ideally maintaining a sense of transparency. Smith-Miller + Hawkinson Architects used curtainwall glazed with insulated cellular thermoplastic polycarbonate panels to enable them to reconcile two requirements seemingly at odds with each other: lightness and explosion resistance.
Normally, one might use ballistics-resistant glass. But it is extremely expensive, particularly when fabricated in insulating glass units. “One of the requirements was that if an explosive device was set off in front of the curtainwall, our structure would meet their [the General Services Administration’s] progressive collapse requirements,” says Laurie Hawkinson, the partner in charge of this project. “You can imagine when you start running the numbers on that, the column and grid spacing starts to get really tight.”
But the architects were able to get the polycarbonate panels rated for blast resistance, the first time this had been done for a federal facility. While presenting his case to the GSA, Sean A. Gallagher, a senior associate at Smith-Miller + Hawkinson, became an expert on the material’s performance properties, from yellow indexing to melting points. Lower cost, resistance to explosions, and insulating value were all points in polycarbonate’s favor. The difference in cost between polycarbonate and ballistic-rated IGUs is “extreme,” Gallagher says—perhaps $40 per square foot versus $350. Once the blast rating was secured, they were able to meet the glazing budget for the building without compromising the need for daylight.
All of the LEED Silver–rated Massena port of entry’s four buildings use the panels to harvest daylight and to gain a luminous appearance at night. Hawkinson says that, initially, the client “didn’t even have daylight on their radar. But they were very pleased that we found a material that could work for them in terms of cost and security.”
The panels are 2 feet wide and some are as tall as 24 feet 8 inches once installed. Typically, these panels are anchored to 2-inch-by-10-inch horizontal steel girts that are spaced 5 feet apart vertically; the girts are welded to columns spaced 15 to 28 feet apart, depending on blast requirements. All of the vertical joints of the panels are backed up by additional steel tubes, and fastened to each other using an exterior batten system of plastic locking strips. These prevent even wind-driven rain from infiltrating the building.
A 25mm-thick cellular thermoplastic panel that is 38 percent light transmissive can achieve an R-value of nearly 2.70, making it competitive with double-paned glass assembled with low-E film. Energy modeling enabled the architects to balance the beneficial effects of daylight through the panels against heat loss. This allowed them to optimize the proportion of higher R-value, less-light-transmissive panels against thinner, lighter panels. The buildings, finished in 2009, use a mixture of both.
Gallagher adds that the modeling program was also extremely helpful in optimizing the geometry of the sloped roofs of each structure and their orientation. “On the administration building for passenger cars, the largest areas of poly are on the north side of the building, and cover the upper portion of the building. The south side has less, to minimize heat gain.” The polycarbonate system was off the shelf, and the aluminum framing system for the polycarbonate sheeting was not custom-designed for the job. However, the clear corner assembly was designed with the fabricator for Massena specifically.
And at the administration building, unlike some of the more utilitarian truck-inspection buildings, polycarbonate is not the only thing standing between occupants and the weather. In some areas of the building, separate walls of ballistic CMU, as well as glass clerestories, stand behind the polycarbonate, increasing the U-value of the wall assembly considerably.
For polycarbonate’s skeptics, Gallagher notes that the material does not change color the way it used to. “The new polycarbonate will not smoke, yellow, or cloud over,” he says. Installed, the cost for the system was about $38 per square foot, according to Smith-Miller + Hawkinson’s cost estimators. The complex came in $4 million under budget.