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Sponsored by Guardian Industries Corp., SAFTIFIRST, Pella Commercial, and EFCO, a Pella Company

Energy codes and green building standards are not the only trends affecting how architects design building enclosures. Far and away, however, they are the most likely to spark permanent change. The new International Energy Conservation Code (IECC), like its predecessors, sets prescriptive and performance paths for achieving better enclosure performance. In addition to the growing stock of LEED-branded properties, the spanking new International Green Construction Code (IGCC or IgCC) has been coordinated with the International Code Council (ICC) family of model regulations. As with the IGCC, recent local or statewide rules such as California's CalGreen add new impetus for architects to adopt best practices for exterior insulation, air barriers and high-performance fenestration.

“The emergence of green building codes and standards is an important next step to provide communities with the opportunity to build sustainable and safe buildings,” summarized ICC's chief executive Richard P. Weiland in March, as communities in Western states began to voluntarily adopt the IGCC.

The energy codes and the new green rules offer fresh, clear guidance to municipal inspectors on a variety of performance indicators. Among the most useful is the baseline performance criteria handed down for windows, storefronts and doorways—places where air leakage, thermal gain and glare from daylight can hamper the goals of sustainable, energy-efficient construction. Add to that the new recognition of fire-safety performance for glass and windows in the 2012 International Building Code (IBC) chapter 7 tables—comparing fire-protective and fire-resistive applications—and local codes will eventually offer better minimum performance than ever before alongside new pathways to high-performance fenestration.

A high-performance aluminum-clad wood window wall at the Environmental Nature Center in Newport Beach, Calif., captures natural ventilation and daylight while limiting heat gain with advanced, low-E insulating glass. Photo by Costea Photography, courtesy of Pella Commercial

Better minimum performance is not the best performance—nor is it the most efficient or greenest possible. Yet there are more ambitious standards that, like the U.S. Green Building Council's LEED program, set design standards as baselines for green construction. Jurisdictions can adopt the rules in the IGCC, CalGreen or ASHRAE Standard 189.1—another green building baseline—for a more aggressive local policy.

The result of all this on fenestration options has been twofold: Improving specification and field applications on the one hand, and encouraging innovations by product developers on the other.

“The IECC and IGCC are really driving how framing assemblies and glazing materials are made,” says Terry Zeimetz, AIA, CSI, CCPR, commercial marketing manager with Pella Commercial. “A new generation of fenestration systems is available with more internal chambers, triple glazing, multiple types of low-emissivity coatings, integral shading and other novel, energy-saving features.”

Source: www.commercialwindows.org/codesstandards_iecc_more.php#2012

“The codes are what really matter, and they don't distinguish between project types,” concurs Chris Dolan, director of commercial glass marketing with Guardian Industries. “Government buildings, institutional facilities and LEED-rated projects all have increasingly stringent energy requirements, so they are all seeking high-performance fenestration with the best-performing glass available.”

More critically, says Dolan and other fenestration experts, the codes and green standards rely on climate zone data to determine energy-efficiency requirements. They may also vary by jurisdiction, according to the Efficient Windows Collaborative (EWC), Minneapolis. “In the 2006 IECC and later, this variation is based on eight climate zones, with each county assigned to one climate zone,” according to the EWC. “However, older versions of the IECC specify 19 different climate zones.” Maximum U-factors and solar heat-gain coefficients (SHGCs) are given in the model energy codes and green-building standards. Skylights are treated separately, and have their own maximum values.

The development of novel fenestration systems, products and materials is the focus of this course. In order to put these innovations in proper context, a general understanding of the energy codes and green building standards—and their underlying building science—is critical.

For this Dept. of Veterans Affair Medical Center in Orlando, Fla., currently under construction, fire-rated glazing has been specified to improve safety and increase daylighting within. Photo courtesy of SAFTIFIRST

Fenestration Performance Factors

Underlying the codes and standards is a well-established foundation of building science related to glazing and fenestration design. A number of those help design teams calculate energy performance, while others relate to safety and fire performance. Among the most important to consider are:

Air leakage

The energy codes and green standards offer guidance to protect buildings from excessive air leakage, often given as maximum levels of air movement in cubic feet per minute (cfm). Poorly designed window-wall interfaces and leaky curtain wall assemblies, for example, transfer heat via air movement in an uncontrolled manner.

U-factor

“Air infiltration is important but distinct from U-factor, which describes the heat transfer rate or insulating ability of an entire fenestration assembly, glazing panel or a window frame,” says Erik S. Sutton, Assoc. AIA, manager of product marketing with EFCO, a Pella Company. “When the temperature inside is different from outside the building, heat will be lost or gained directly through a window. U-factor is the overall rate of heat movement.”

Courtesy of EFCO, a Pella Company

High-performance low-E glass was specified for Ashton Judiciary Square, Washington, D.C. Photo courtesy of Guardian Industries

Solar heat-gain coefficient

Direct sunlight on fenestration also adds heat to the building interior through solar radiation, even on the coldest winter day. Glass and window assemblies can control this heat gain to a predictable extent, says Guardian Industries' Dolan, defined as solar heat-gain coefficient, or SHGC.

Visible light transmittance

To calculate how much daylight will be available inside a building to offset electrical lighting needs or to address potential glare, the measure visible light transmittance (VLT) provides a basis for comparison.

Fire-protective and fire-resistive glass ratings

While not associated directly with energy consumption, fire ratings for glass provide a means for comparing the ability of fenestration to protect building occupants and property against fire.

To allow for daylight opportunities and maximize lines of sight, for example, fire-protective and fire-resistive glass can be applied in areas where traditionally only opaque, fire-rated construction materials have been used. “We are seeing fire-rated glass used in stairwells, occupancy separations, exit corridors and property line applications,” says Diana San Diego, director of marketing for SAFTIFIRST, a U.S. manufacturer of specialized glass for fire-rated applications. “Now, designers can use fire-rated glass to bring natural light into a space, allow it to penetrate further into the building, and even lessen electrical lighting loads by sharing artificial lighting between spaces separated by glass, while still meeting all the fire-rated requirements of the application.”

Electrochromic glazing provides a range of operating conditions, including lower VLT (transmittance) and lower SHGC in its tinted, or activated, state. Image courtesy of Guardian Industries

These performance indicators help describe the control of fire, light, heat and air movement in the building envelope and interior separations. The ability of fenestration systems and materials to control environmental factors is an important criterion for successful building designs.

A Raft of Glass Innovations

Next-generation vinyl windows provide advances in thermal control such as triple-pane glazing and more insulating air chambers. Photo courtesy of K. Easley, courtesy of Pella Commercial

Better ratings and test values are an important trend but they are not the only reason that fenestration products are improving. “In five to 10 years, buildings are going to be very different than they are today because of the energy requirements we face,” says Barry B. Corden, senior director of product applications for Guardian Industries. “So all kinds of technological transformations will really change the game, including building-integrated photovoltaics, or BIPV, as well as electrochromic glazing.”

Several of the newer technologies add renewable and self-sustaining energy production to building designs, says Corden, an outgrowth of the net-zero-energy building movement. Net-zero-energy designs, which dramatically reduce the carbon footprint of the structure, use methods to maximize efficiency while also using onsite electrical generation or water reuse, or both, according to the National Renewable Energy Laboratory (NREL), Golden, Colo. In the new green building codes, the use of renewable energy is encouraged and rewarded.

In the past, solar cells blocked daylight transmission—which reduced solar gain but also increased the use of electrical lighting, all things equal. Next-generation photovoltaic glass materials have been designed for greater transparency, increasing direct and indirect daylighting—which trims electrical lighting needs—and enhancing visibility through the envelope while also more efficiently generating electricity. Where solar cells were previously limited to only rooftop arrays, now the PV glass panels can be integrated into curtain wall, windows, spandrel panels, skylights and roof windows, says Corden. The maximum panel size today is about 5 feet by 5 feet.

While BIPV is a game-changing technology, other incremental advances are just as significant, notes Pella's Zeimetz. Next-generation vinyl windows, for example, are potentially very high-performing fenestration systems today in spite of their longtime association as a cost-conscious alternative spec.

The University of Michigan C.S. Mott Children’s Hospital and Von Voigtlander Women’s Hospital was designed by the firm HKS to use low-E glazing with low reflectivity and a neutral appearance. Photo courtesy of Guardian Industries

The main reason? Advances in thermal control, say fenestration experts. Thanks in part to the use of triple-pane glazing, vinyl windows have been shown in recent studies to be up to 83% more energy efficient than past models (calculated based on U-factors for a next-generation vinyl window with advanced low-E triple-pane insulating glass with argon compared to a single-pane vinyl window in winter conditions). “State-of the-art product designs have up to 18 insulating air chambers within the vinyl window frames—that's three times more than typical vinyl windows,” says Pella's Zeimetz. The result is a total window unit U-factor of as low as 0.15, which compares to the 2012 IECC maximum U-factors for vertical fenestration of 0.29 and 0.37, respectively, for fixed and operable units, in the most stringent climate zones.

The Sapphire Towers in San Diego have glazed openings with a minimum 45-minute fire rating. Photo courtesy of SAFTIFIRST

In addition, new vinyl and aluminum windows can be specified with optional foam insulation to further improve the energy performance. To improve control of solar gain and daylight glare, new window designs can include shades or blinds between the glass panes. This feature generally reduces solar heat gain while also protecting the solar control layer from degradation, wear and tear, and mishandling by occupants. Most importantly, it brings the solar protection layer closer to the building exterior, which improves thermal control and occupant comfort.

In fact, the position and location of the active fenestration layers, such as the low-emissivity (low-E) glass coating, can significantly improve enclosure performance, says Guardian's Dolan. “A new low-E glass coating designed for interior glass surfaces is designed to reflect heat back into the building, which further reduces the U-factor,” he explains. “So for a typical double-glazed unit, an architect can achieve a center-of-glass U-factor of 0.20, which is an R-factor equivalent of R-5.”

The secret to the innovation is a highly resilient interior-surface low-E coating that is not composed of a silver-based compound. The durable, scratch-resistant surface will not corrode like typical low-E coatings, so it can face the building interior surface rather than the insulating glass unit (IGU), which has been typical.

Another type of glazing innovation, electrochromic glass, also helps to control SHGC, VLT and U-factor. “Electrochromic glazing technology can be switched on demand from clear to variable-tint states, giving occupants and owners unprecedented control over the amount of light and heat that enters a building,” says Guardian's Corden. “This switchable tinting capability delivers environmental benefits, improved occupant comfort and potential operating cost reductions.” The product also allows architects to eliminate blinds, shades and other window treatments that may reduce outdoor views, he adds.

Assemblies Advance

In addition to better glass formulations, a number of improvements motivated by stringent codes and industry technical advances have been applied to storefront and curtain wall. Some unitized curtain wall systems now offer novel, integral vent windows, for example, to allow for more fresh air circulation to improve IEQ. A novel unitized aluminum curtain wall, for example, takes advantage of a proprietary, high-strength fiberglass composite technology developed originally to resist thermal expansion and contraction.

Used as struts in the unitized curtain wall, the five-layer composite helps achieve excellent U-factors, says EFCO's Sutton. It can also be employed for the pressure plate, providing thermal conductance values approximately 300 times better than those for aluminum plates. The composite has also been shown to improve thermal conductance and overall frame and glass U-factor gains of about 27 percent versus standard aluminum pressure plates. The material swap can also reduce installation steps, because it eliminates the need for a thermal isolator between the back member and pressure plate.

At the Cornell Physical Science Building in Ithaca, N.Y., novel thermal breaks, some using composite materials, provide lower overall rates of heat transfer and better U-factors. Photo courtesy of EFCO, a Pella Company

 

Introducing greater levels of fresh, outdoor air into occupied interior zones is known to improve occupant health and productivity. To improve indoor environmental quality (IEQ) through the fenestration choice and design, architects may select a high-performance architectural-grade vent, also known as an AW-rated vent, that is integral to the curtain wall system.

Another novel fenestration product is an aluminum-clad wood window wall with a wood or steel structure for structural attachments. The system design provides structural, technical and water-management capabilities while offering a wood interior and an aluminum exterior. In some cases, the aluminum-clad wood products are tied to the building structure using steel tubes or similar metal connections.

Beyond structural integrity of the fenestration systems, predictable performance under heat, flame and smoke during fire emergencies is important for code officials in order to allow the use of glass for fire-rated fenestration, exterior walls and interior partitions. That need—in addition to the desire to maximize exterior views and daylighting within the building for further improvements to IEQ—has led to the increased use of fire-protective and fire-resistive glass.

According to SAFTIFIRST's San Diego, these glazing materials must meet the standards published by West Conshohocken, Pa.-based ASTM International, the Quincy, Mass.-based National Fire Protection Association (NFPA), and UL, formerly Underwriters Laboratories. “Fire-protective glass meets NFPA 252/257, protects against smoke and flames, and is typically used in 20- to 45-minute applications. Fire-protective glass is limited to 25 percent of the wall area because it is unable to block dangerous radiant heat,” she explains. “Fire-resistive glass, on the other hand, meets ASTM E-119/NFPA 251/UL263 and protects against smoke, flames and dangerous radiant heat. It is typically used in applications of greater than 45 minutes and has none of the size limitations that apply to fire-protective glass.”

In other words, the fire-rated glazing products can be used in stairwells, exit corridors, rated walls between dissimilar occupancies, and other fire-separated areas in a building. “On the building's exterior, fire-rated glass can be used whenever property line requirements need to be addressed, or if the area is in close proximity to a parking garage,” says San Diego. The latest fire-rated fenestration assemblies are available for hurricane zones, ballistic applications, and even energy-efficient applications. Some fire-rated glass systems have glass and framing assemblies certified by the Greenbelt, Md.-based National Fenestration Rating Council (NFRC) as a response to the increased demand in energy-efficient building enclosures.

This fact ties back to the original premise of many innovative fenestration products: to meet and exceed multiple energy code regimes and green-building standards while still providing occupant safety, security, sound control and privacy.

Prescriptive vs. Performance

In applying innovative fenestration technologies, architects are served best by understanding applicable energy codes and green building standards, both required and voluntary. Compliance paths are varied, but in many of the codes and programs include both prescriptive and performance-based options.

The IGCC, for example, is written in mandatory language that allows jurisdictions to specify enhanced performance levels in very specific areas of concern. For energy systems, buildings over 25,000 square feet must use the performance-based energy compliance path, which exceed the 2012 IECC; projects smaller than that can be designed using prescriptive or performance based compliance. Fenestration requirements, however—which are covered in IGCC Section 606, along with U-factor alternatives, air infiltration and other building thermal envelope features—apply to the prescriptive-based compliance path only.

Source: CommercialWindows.com

 

In general, the IGCC's requirements affecting fenestration include energy conservation levels, air infiltration rates, daylighting measures and total renewable energy, which may include BIPV fenestration systems, glazings and the like. All fenestration must comply with the 2012 IECC limits on air leakage. For the prescriptive path, the total building envelope system (including fenestration) must beat the 2012 version of IECC by 10 percent or better, and it must have permanent shading on all but the north façades.

The IGCC also gives ASHRAE 189.1 (officially known as the ASHRAE/USGBC/IES Standard 189.1-2009) as an optional compliance path, which allows for a performance-based assessment of building energy efficiency using modeling software or a prescriptive path with a maximum allowed fenestration area (40 percent of exposed exterior walls) and minimum performance levels for such fenestration variables as air leakage rates, SHGC and U-factor.

The prescriptive levels in ASHRAE 189.1—and, by extension, in the IGCC—are viewed by some as quite aggressive. For example, in climate zones 1, 2 and 3, where air-conditioning loads predominate, permanent shading devices must be installed and the maximum allowed fenestration area on east- and west-facing exposures must not exceed a specific limit depending on how much fenestration area is on the north and south exposures. In all situations, skylight area may not exceed 5 percent of total roof area, but daylighting using skylights must exceed a certain minimum level in certain large interior volumes.

That's not all. Windows and skylights may not have air leakage rates greater than 0.4 cfm per square foot. There are also minimum SHGC requirements that take into account building-integrated shading and skylights used for daylighting. Further, occupancies such as schoolrooms and offices must provide a minimum effective aperture for vertical fenestration (EAvf), which can be met by using high-VLT fenestration or by increasing glazing area, or both.

In the 2012 IECC, mandatory air leakage maximums are given for both the prescriptive and performance versions. If the prescriptive path is elected, there are specific requirements and levels for SHGC, U-factor and total fenestration area – 30 percent, unless daylighting design is integral to the building enclosure. The use of automated controls for daylighting increases the allowed areas for windows, skylights and the like, but only if more than half of the interior floor area is designed for daylighting and if the fenestration VLT is at least 1.1 times the SHGC, according to the the University of Minnesota's Center for Sustainable Building Research (www.commercialwindows.org) in Minneapolis.

Underlying all of the fenestration requirements in the IECC, IGCC and ASHRAE 189.1 are fenestration energy ratings, which are set forth and promulgated by NFRC. Any testing lab that meets NFRC standards can certify the product ratings, according to Center for Sustainable Building Research. “Regardless of the chosen compliance path, the following fenestration energy properties are critical for compliance with the code: U-factor, solar heat gain coefficient (SHGC), air leakage, and possibly visible transmittance,” according to the research site established by the university with Lawrence Berkeley National laboratories.

Case Studies of Fenestration Innovations

Looking to the prescriptive code minimum of IECC or the more ambitious performance targets in the IGCC—as well as the new ICC fire ratings for glass—architects around the country are using innovative fenestration technologies and design techniques to create sustainable, energy-efficient and safe buildings. A number of new case studies provide examples of the goals and application strategies.

Glass Product Selection Criteria

Radiant energy transfer is the key to the selection of glazed fenestration. Four properties contributing to radiant energy transfer are transmittance, emittance, reflectance and absorptance. As its name suggests, emittance is the property that is addressed by low-emissivity (low-E) glass. Yet all areas of a window assembly or curtain wall may affect the types of performance expected for radiant energy transfer. Three of the four properties also contribute to the overall performance of glazed fenestration: Solar Heat Gain Coefficient (SHGC) The tendency of a fenestration assembly to resist gain heat caused by direct or indirect solar radiation is measured quantified by SHGC. Visible Light Transmittance (VLT) Visible light transmittance describes how much visible-spectrum light comes through a glazed assembly. More visible light generally means more daylighting opportunities—and higher heating loads and more potential for glare. U-Factor The U-factor essentially describes how well a fenestration assembly insulates the building, similar to an R-value. Instead, though, it summarizes the window or skylight’s total rate of heat transfer. From indoors, a window with an excellent U-factor will not be as cold to the touch in winter as a similar window with poor U-factor.

Fire-Rated, Energy-Efficient IGUs: Sapphire Towers, San Diego

The designer and owner of this luxury high-rise condominium in San Diego hoped to offer panoramic views of the bay and waterfront, with the largest possible window openings. Yet, the building's south elevation was too close to the adjacent property and required a solid—and presumably opaque—enclosure system. As an alternative, the code allowed glazed openings with a minimum 45-minute fire rating on all 32 floors. The architect, AVPR Studios, selected fire-rated, NFRC-certified assemblies on all floors, meeting both the fire and energy requirements using just one system—182 units in all, ranging from 48 by 90 inches to 82 by 130 inches in size. The outboard lite is a 1/4-inch blue glass matching the rest of the tower, but on the south façade it is combined with a 3/4-inch, 45-minute-rated glass with a low-E coating on the No. 3 surface. The assembly uses fire-resistive GPX framing with aluminum covers, finished in a silver powder coat for the exterior side and white powder coat for the interior side to match all the non-rated framing used in the project. The general contractor, Swinerton Builders, and the glass installer requested the IGUs be delivered as preassembled, modular units to improve quality control and reduce risk on the job site.

Aluminum-Clad Wood Awning Windows: Environmental Nature Center, Newport Beach, Calif.

The window wall and outswing doors used for the LEED Platinum Environmental Nature Center comprise fixed and operable casement and awning windows with green-tinted, low-E insulating glass that reduces glare and solar heat gain while maximizing visible light transmission. Photo courtesy of Pella Commercial As the first LEED Platinum building in California's Orange County—and one of only 10 or so Platinum certificants in the entire state—the 9,000-square-foot, $4.2 million, nonprofit Environmental Nature Center (ENC) is an educational facility focused on exposing the natural world to visitors. With that in mind, the architect and ENC board hoped to make the building a showplace of sustainability and energy efficiency. Using a palette of recycled and recyclable materials including insulation from old blue jeans and a composite wood skin made of organic sawdust and natural resin, the architects at LPA in Irvine, Calif., created a stunningly simple shed roof with expanses of large operable and fixed aluminum-clad, wood awning windows to create a window wall. To keep the project on its tight budget, the architects had planned to orient the building east-west to capture natural ventilation through the building—enough to completely eliminate the need for heating and air-conditioning. The window wall and outswing doors used for the project were specified and designed, with help from the manufacturer, as fixed and operable casement and awning windows with natural wood interiors and custom-color, low-maintenance aluminum-clad exteriors. An advanced, low-E insulating glass design with a green tint was selected to reduce glare and solar heat gain while maximizing visible light transmission. Overall, the fenestration design helped earn the project LEED points for energy efficiency and IEQ.

Low-E Glazing, University of Michigan Stadium, Ann Arbor, Mich.

For a renovation of a large collegiate athletic stadium, the right glazing spec was essential for the lead architects, HNTB Architecture. The designers selected a high-performance, energy-saving low-E glass product for more than 50,000 square feet of façade and entrance area. The glazing work was coordinated with renovations of the distinctive facility, include a new press box, new towers and luxury boxes. The low-E glazing was selected for its neutral appearance, solar control capabilities, and significant energy savings that would result from its heat emittance qualities. In many situations, the glass looks like standard float glass. According to John Peterkord, associate vice president and senior project manager for HNTB, “The selection of the glass was extremely detailed, with dozens of samples of glass of different types and colorations. We narrowed the selection down to just a few and then used large mock-up panels,” made by the suppliers.” The mockups were set into place so that the architects and university representatives could evaluate the options under typical environmental conditions. Though it looks like typical float glass, the specified glazing panels provide very low SHGC, reduced interior glare, and good light transmission. The end-result is the ability to balance the need for natural daylighting indoors with the need to keep environmental conditions balanced—both important components of IEQ. For Pinellas County Courthouse in Florida, the architect selected architectural-grade, double-hung windows custom-manufactured to match the original sightlines. Photo courtesy of EFCO, a Pella Company

High-Performance Historic Profiles: Pinellas County Courthouse, Clearwater, Fla.

For a 1917 courthouse building in Clearwater, Fla., the project design team faced the common conflicting needs to bring windows up to current codes—including structural loading and large missile impact requirements—while also protecting its historic integrity and landmark status. Pinellas County Courthouse required architectural-grade, double-hung windows custom-manufactured to match the original sightlines closely enough that it would difficult for the untrained eye to notice that a renovation had taken place. In addition to matching the sightline, two different colors had to be used on the window cladding: mahogany on the interior and green on the exterior. The exterior trim was reproduced by using the original wooden sash lug with an aluminum extrusion, specified by the architect Renker Eich Parks Architects of St. Petersburg, Fla. The replication of the intricate detail of the wooden trim on the exterior and interior was accomplished by combining several extrusions in a panning system custom fitted to each opening. Long-term durability and life-cycle performance were considered in this public-sector project. For good thermal performance, special isolators were employed in the window construction, which had the added benefit of allowing the interior and exterior window extrusions to be finished in two different colors, as required by the architects based on the building's original color scheme.

Conclusion

From basic concepts such as reducing air leakage to high-tech novelties such as electrochromic glazing, projects such as these demonstrate the advantages of using innovative fenestration materials and assemblies to meet project goals. Many of them allows the architect and client to address multiple goals—including energy code adherence and sustainable building needs—with a single specified item.

Chris Sullivan is principal of C.C. Sullivan, a communications consulting and marketing agency focused on architecture, construction and building products. www.ccsullivan.com

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Learning Objectives

At the end of this course you will be able to:

List key energy codes and green building standards that impact fenestration selection, and their underlying metrics. Explain how various fenestration technologies have been adapted or developed to meet the goals of energy efficiency, green building and fire-safe construction. Discuss how fenestration systems and glazing materials may be specified to meet prescriptive and performance-based energy codes or green building standards. Describe one or more case studies showing how fenestration systems can meet energy efficiency or green building goals.

Credits: 1.00 HSW/SD

This course was approved by the GBCI for 1 GBCI credit hour(s) for LEED Credential Maintenance.

Course Outline:

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