Nuanced Solutions for Greener Façades
Material choice and specification begins with top-level issues, such as desired color or appearance, and related aesthetics, such as the need for matching vision and spandrel glass, says Guardian's Dolan. “Glass can be specified as clear, but newer low-iron glass formulations are even more clear than those standard glazings marketed as clear, offering a more neutral and less greenish look,” he explains. Glass colors such as light gray, gray, green, and others are also available, all with low-E coatings. “Because of advances in low-E technology in recent years, as many as five to 18 layers of metal or metallic oxides can be deposited onto the glass surface, boosting its performance.” These include new “triple-silver coatings” that yield an attractive neutral/blue reflected color yet boast a low SHGC of 0.23—meaning that 77 percent of the solar energy is blocked—while allowing 51 percent light transmission.
In spite of these very high performance levels, architects are also considering alternatives. “While the glass industry has been adding exotic treatments to their formulations to improve performance, polycarbonate is naturally good at insulating and rejecting solar heat gain,” says EXTECH's Strait. “For applications such as clerestory openings in gymnasiums, industrial facilities, or any place that does not require visual access, translucent polycarbonate glazing admits high levels of natural light while eliminating glare.” In addition, polycarbonate—made from thermoplastic polymers—is shatterproof, easily molded to various shapes, and can be color-matched to a particular design scheme. Properly integrated into an engineered framing system, polycarbonate glazing is effective in reducing air infiltration, controlling moisture entry, and meeting any required codes.
Other glazing innovations like these are boosting the WWR for new buildings while keeping energy performance within tight ranges. Dolan notes that pre-painted glass in very large sizes is now available for spandrel applications. These manufacturer-painted panels are then cut and heat-treated by fabricators—some of which don't paint glass or previously required longer lead times to do so—making it easier to improve glass matching on the façades.
Whether spandrel or clear or coated glass, the ever-larger panels are helping accommodate the trend toward larger IGUs and lite sizes. Bigger units mean reductions in the number of frame components and amounts of field labor as compared to traditional systems. For example, while a 30-foot opening might typically require six modules, now they are commonly achieved with two or four units that have steel reinforced members, depending on seismic and wind load requirements. With larger openings come greater demands on manufacturer and contractor quality, cautions Haber of W&W Glass—and this in a market that still exhibits a post-recessionary “hangover” accustomed to commodity pricing and generic performance levels.
“Large-span façades are all about glass engineering,” says Haber. “Yet the design team is facing quality issues in glass fabrication such as roller-wave distortion due to softening from the heat-treating process and nickel sulfide spontaneous breakage, a catastrophic failure seen in heat-tempered glass with nickel sulfide contamination.” While a heat-soak process is used by most U.S. and European manufacturers to reduce or eliminate potential breakage, Haber says that some Chinese glass suppliers are distributing low-cost glass with dramatic increases in nickel sulfide content, resulting in significant instances of onsite breakage.
In addition, cost and warranty issues loom larger as glass panels get bigger, Haber notes. “Oversized glass manufacturing, packaging, shipping, and installation are inherently riskier and more expensive, and also limit the number of vendors who can make the product,” says Haber. “To limit liability, architects and their project teams should start out with a solid, performance-based specification with prequalified vendors and then pick the right product, always insisting on a manufacturer's warranty for the system, not a warranty from the subcontractor, who is really just a system amalgamator.”
Unitized, Pre-Engineered Systems
With these quality and liability issues in mind, an increasing number of architects are specifying unitized products where site-assembled once predominated. “More and more mid-size façades are using unitized solutions on smaller projects, such as four- to eight-story buildings, which traditionally would be stick-built and are now more often unitized,” says Kawneer's Hunter. “The reasons are that today, the glazing skills are harder to find depending on the area of country, and the glazier's trade is handed down from generation to generation rather than taught in schools.”
Photo courtesy of Simonton Windows & Doors
For the LEED-certified Elizabeth Seton Pediatric Center, a long-term-care facility for 130 children in Yonkers, New York, the firm Perkins Eastman specified crisp, white vinyl frames for new picture windows and casements using low-E glass with argon gas fill.
So more contractors want to unitize their low- and mid-rise projects, which brings the added benefits of improved quality control and by having the ability to closely monitor labor in a shop environment vs. in the field. It can also accelerate the scheduling, helping the contractors enclose the buildings faster and expediting occupancy. “But it takes more pre-planning and you have to get all shop drawings completed and approved so that manufacturing can start earlier in the project sequence,” Hunter adds.
Quest Window's Cash agrees, adding that about 30 percent of the company's unitized façade systems are specified as opaque openings, similar to Kawneer's approach offering aluminum composite material (ACM). The same is true with polycarbonate glazing systems, adds EXTECH's Strait, which are sometimes combined with glass panels for variety, view, and increased visible light. “We pre-fabricate the entire glazing system in our shop, so that it arrives at the jobsite ready to install. We eliminate the uncertainties associated with field fabrication,” says Strait. “Deep glazing rabbets and low-friction gaskets help the façades maintain an effective seal against air and water infiltration, while allowing for thermal movement of glazing.”
Manufacturers of unitized systems also offer a variety of specification and installation services to help smooth the project work. This typically starts with engineering support in the design phase followed by an optional mock-up phase, which many façade consultants recommend, noting that it is a required element of building enclosure commissioning (BECx). Later, the product manufacturers offer installation guides and field support to contractors and the trades. Some even offer training and certifications in their particular specialties.
In addition to product laboratory testing and project field checks, the mock-up helps “verify that the individual systems are assembled and installed appropriately, [and] that all systems will function interactively to meet the project goals,” according to Rick Ziegler, P.E., a BECx expert with engineering firm Smith Seckman Reid. “The testing conducted is typically not as comprehensive as laboratory testing, but can include structural, seismic, thermal, durability, air infiltration, and water penetration.” Mock-ups can be valuable for both stick-built and unitized systems, though the unitized systems tend to benefit from more lab review, reducing issues found in the mockup tests.
Photo courtesy of Lorin Industries Inc.
To restore and resurface the Mercedes-Benz Superdome after Hurricane Katrina, the architect Brad McWhirter, AIA, of Trahan Architects, specified 365,000 square feet of anodized aluminum panels colored to match the 1975 original façade.
Touting this benefit, a number of door and window makers offer industry-standard certifications for product performance and integrity, says Simonton's Steven Saffell, a technical expert. “AAMA's Gold Label certification states who manufactures the product and to what levels it has been tested, and the information is publicly available on their website,” he explains. “This gives the end-user confidence that can't be matched by self-certification or other audits that don't have an independent third party involved.” According to AAMA, its certification program and familiar Gold Label are required by many federal, state, and municipal building codes and administrators.
Notice
www.EFCOCorp.com
www.FiFoil.com
www.extechinc.com
www.fundermaxusa.com
www.SunGuardGlass.com
www.kawneer.com
www.lorin.com
www.simonton.com
www.ecowall.questwindows.com
www.wwglass.com