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Trending High Winds, Curtainwalls and Glazing Updates

Keep current on curtainwalls and glazing and how they protect against high winds

Ykk Ap Nov18 1
PHOTO COURTESY OF YKK AP AMERICA INC.

One of the functions of a curtainwall and its glazing is to withstand wind loads and transfer them to the structure to which it is attached. In recent years there have been important updates, innovations and improvements on curtainwalls’ ability to do this.

These trends are growing in importance throughout the country; it’s a common misconception that curtainwall systems designed for high winds and hurricanes are only required in Florida. “They are, in fact, needed in other hurricane-prone regions as well,” says Jeff Ziesche, brand manager, CRL-U.S. Aluminum, Los Angeles. “This includes states in the Gulf of Mexico, as well as those on the Eastern Seaboard, up to Massachusetts. Florida is highly prone to hurricane weather but not all areas in Florida require impact systems, particularly in the mid-north such as Madison and Hamilton counties. Take note of the building’s exact address and check with the local code compliance office.” Successfully adopting these building codes is critical for very high wind/hurricane areas.

APPLICABLE DESIGNS

First-generation curtainwall system designs specific for high-wind impact appeared in the 1990s. Their choices were limited, offering curtainwall, storefront and entrance systems designed to the upper end of design pressure requirements. As the industry matured, new systems designed for a broader range of design pressure capabilities appeared. “South Florida has more stringent test protocols, but they also experience much higher wind speeds and more destructive storms,” says Greg Galloway, ProTek brand manager, YKK AP America Inc., Austell, Ga. “Overdesigning for any performance-based specification can result in adding cost without much incremental value. In the last few years, we are seeing an increase of designs more closely matched to the level of protection needed.”

YKK AP recently launched a hurricane impactrated window wall system. Window wall systems have long been recognized as filling an important niche between storefront and curtainwall. Window wall systems can provide similar aesthetics to curtainwall (using optional slab edge covers) with lower material cost and rapid installation time. “They have long been the system of choice for multifamily condos and apartment buildings,” Galloway says. “A key attribute is inside glazing either at the job site or pre-glazed, ideal for mid-rise buildings. Window wall systems in non-impact areas typically are installed side-to-side and can move slightly after installation. To pass cyclic pressure testing, an impact-rated window wall must have interlocking two-piece mullions that install smoothly and rapidly, a key feature with YKK AP’s YHW 60TU. The system is also rated for design pressures up to 90 psf.”


PHOTO COURTESY OF CRL-U.S. ALUMINUM

GLASS UPDATES

“In commercial construction, storefront and curtainwall products are designed and tested utilizing laminated safety glass to prevent the breach of the building envelope due to flying debris and higher wind pressures associated with hurricanes,” says Kevin Haynes, architectural representative, Tubelite Inc., Walker, Mich. Standard curtainwalls generally consist of two to three panes of monolithic tempered glass, while hurricane-resistant curtainwalls require an outside monolithic-tempered glass pane and an inside laminated glass pane.

“[Because] hurricane-resistant curtainwalls require laminated glass, traditionally, a polyvinyl butyral (PVB) interlayer is used,” Ziesche says. “However, we’re seeing ionoplast interlayers being specified more and more. Ionoplast has five times the tear strength and 100 times the rigidity of a conventional PVB interlayer. This translates to reduced deflection and superior post-glass breakage performance.”

Kevin Smith, director of product development and application at Exterior Technologies Inc. (EXTECH), Pittsburgh, says monolithic polycarbonate is a common glazing material for canopies and awnings. However, he contends that very high wind speeds result in very high component cladding loads requiring thicker sheets of polycarbonate to carry these loads. “Many thicker monolithic polycarbonates cannot meet the flame propagation performance requirements of the code (IBC section 3105) for canopies and awnings,” he adds. “Cellular polycarbonate systems, such as our 3100LS and 8000 systems, can meet both the flame and load requirements. [These] are still relatively new to the U.S. market compared to glass or FRP (fiberglass reinforced plastic) systems. Cellular polycarbonate has outstanding impact resistance against flying debris.”

Cellular polycarbonate systems provide an updated look, as opposed to the typical grid appearance of FRP systems, or the glass systems that rely on more horizontal mullions in both wall and canopy applications. “Cellular polycarbonate systems allow for long (up to 54 feet,) vertically oriented, glazed panels, which eliminate numerous leak-prone horizontal mullions,” Smith says. “This is especially critical in low-sloped canopy applications, where mullions placed perpendicular to the flow of water can create water dams, dirt pockets and potential leaks. As a flexible glazing material, the allowable deflection limits for the building structure can be greater with cellular polycarbonate systems than are allowed with glass.”

There is a noticeable trend in using hurricane impact-resistant curtainwall systems like Tubelite’s ForceFront Storm Curtainwall that incorporates larger glazing pockets to accept the laminated safety glass that can be glazed utilizing the wet-seal (applied structural silicone sealant between the edge of glass and back member) or dry-glazed (full gaskets) method. “The architect/design professional can select between fully captured with face caps, or two-sided or four-sided SSG (structural silicone-glazed glass is butt-jointed together) on the curtainwall’s exterior allowing for more flexibility in the overall appearance,” says Tom Mifflin, product manager at Tubelite.

YKK AP recently launched the YHC 300 SSG Cassette. This insulating glass unit is glazed on all four sides with structural silicone to an aluminum carrier frame in an environmentally controlled shop environment. “Curtainwall framing is stick-built in the field and the glazed cassettes are mechanically attached in the field,” Galloway says. “Unitized curtainwall provides the same aesthetics, but may not be economically feasible for smaller or nonrepetitive jobs.”

For support, hurricane-resistant curtainwall systems utilize a more robust anchoring system with additional fasteners. “Aluminum extrusions are heavier and deeper—typically from 7 to 10 inches,” Ziesche says. “This helps the system maintain structural integrity when exposed to high winds. You’ll also see deeper glazing pockets, which increases glass bite.”

PHOTO COURTESY OF TUBELITE INC.

PHOTO COURTESY OF EXTECH

OTHER UPDATES

Inside glazing can have a negative effect on overall system performance in high-wind areas. “That’s why almost every hurricane-resistant curtainwall is outside glazed,” says Ziesche.

While Galloway agrees that outside glazing has historically been the most common installation method for storefronts and curtainwalls, he sees pre-glazing or fully unitized construction becoming more popular for a number of reasons. A key advantage has always been that critical seals are done in an environmentally controlled atmosphere. “A more recent driver of the trend toward pre-glazing is the difficulty in finding and keeping good people,” he says. “Building in a shop or factory setting is inherently more labor efficient than field fabrication and glazing. Plus, with pre-glazing, many steps can be automated. As one customer said ‘I can buy equipment; I can’t hire people.’ A relatively new influence to go the pre-glaze route is time on the job site. As owners and general contractors see more preglazed and unitized construction, they more fully appreciate the value from drying in the building faster.”

Another trend in hurricane-impact curtainwall systems is providing natural ventilation with zero sightline vents. Four-side SSG allows the window frame to be hidden so all you see from the exterior is the glazing. “The exterior sightline is unchanged and unless open, the window blends into the façade,” Galloway says. “Typical commercial windows readily install into curtainwall systems, but aesthetically there is a large sightline at every location where a window is installed.”

UNDERSTANDING UPDATES

To better understand and benefit from updates, always consult with manufacturer(s) as early in the design process as possible. “[Many] manufacturers’ websites provide a quick overview of hurricane impact- resistant protective glazing products,” Haynes says. “Product overviews include system descriptions, and application limitations regarding maximum design pressures, frame sizes (frame heights and vertical mullion spacing) and glass sizes. [Also], an architect can visit the Florida Building Code Online (www.floridabuilding.org) and the Texas Windstorm Insurance Association (www.twia.org) to access approved products.” Ziesche concurs that architects should contact their local Authority Having Jurisdiction (AHJ) early in the design phase

Wind damage to Sebring Fla. home caused by Hurricane Irma. Photo by John L. Carkeet IV, LimpingFrog Productions, courtesy of AAMA