Creating High-Performance Building Facades

New materials, products, and systems create better results that enhance designs
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Sponsored by Azon, HOFMANN FACADES, Inpro, Neolith®, and Vitro Architectural Glass
By Peter J. Arsenault, FAIA, NCARB, LEED AP

Energy-Conserving Fenestration Systems

Fenestration usually figures prominently in most building facades. This can include windows, doors, louvres, vents, wall panels, skylights, storefronts, curtain walls, and sloped glazed systems. For any of these systems to be installed in a building facade, they need to have a manufactured frame to hold them in place and secure them to the rest of the building. In most commercial buildings, the material of choice is usually an aluminum frame or support system of various types. The reasons for its use are based on its lightweight but inherently strong nature as a material, its ability to avoid rust or corrosion, its rather economical workability, and the variety of colors and finishes in which it is available. However, it is also an excellent conductor of heat, which makes its use on building facades a concern when addressing energy-conserving design and compliance with energy codes, as the aluminum acts as a thermal bridge between inside and outside. This is true in both cold and warm climates as well as extreme weather conditions.

Manufacturers of aluminum framing systems for fenestration have been addressing the thermal issue for decades and continue to develop products that maintain their structural integrity while offering improved thermal performance. The key component is the addition of a thermal break or barrier in the aluminum frames, usually in line with the location of glass or other glazing in the frame. The intent is that the interior and exterior portions of the frame are separated with a structurally rigid but less thermally conductive material. The details of how that break is created and the choice of materials used are what tend to differentiate various products from each other.

Commonly, there are three choices of material used as thermal breaks or barrier material in commercial fenestration systems: vinyl plastic, polyamide nylon, and polyurethane polymer. Each has different thermal and structural properties, so finding the best choice is a combination of understanding these properties and the way they work with the details of a particular aluminum frame profile. This relationship is what manufacturers work on improving and perfecting to provide products that are reliable, economical, and functional.

Photo: © Paul Cosby Architectural Photography; Image: © Tubelite Inc.

The aluminum framing used in fenestration systems include tested and proven thermal breaks or barriers to improve thermal performance while maintaining structural integrity and overall performance.

Of late, polyurethane has received a good bit of attention as a thermal-barrier material in aluminum frames since it can provide superior thermal performance to other choices. For example, using standard test procedures based on the National Fenestration Rating Council (NFRC) 101, U-factors of frames with different thermal-barrier materials can be determined. In a comparison of thermal conductivity of materials according to ASTM C518 standard test method, polyamide 6.6 with 25 percent glass fiber showed a thermal conductivity of 2.08. By contrast, a vinyl barrier produced a better (i.e., lower) result at 1.18, while polyurethane performed the best at 0.84. The significance of the differences in performance, as it relates to the design of the aluminum frame, is that a lower-conducting material will not need as wide a gap to achieve a targeted thermal performance. For example, in at least one frame comparison, a polyamide thermal barrier was used to achieve a U-factor of 0.39 but required a 24-millimeter gap to do so. By contrast, a polyurethane barrier was used to also achieve a U-factor of 0.39 but only required a 15.8-millimeter gap. A smaller gap can mean better structural performance of the frame and possibly thinner overall profiles of products. Hence, achieving better thermal performance in thinner breaks has advantages when seeking to create better fenestration products that allow better sightlines, more structural integrity, and durability.

The most proven approach to effectively install the thermal-barrier material that isolates the inner and outer frames is referred to as a “pour and de-bridge” process. This is based on first creating an extruded aluminum profile that has been designed with a strategically placed channel in the middle of the frame piece. This channel is typically U-shaped and open to the top to receive the thermal-barrier material. Once ready, the thermal-barrier material is installed using specialized equipment designed for this purpose. If polyurethane is used, then it is literally poured in liquid form into the predesigned channel. Then, within minutes, polyurethane solidifies into a very strong structural polymer. The final step in the process cuts and removes the metal thermal bridge from the bottom of the channel to produce a true, non-metal-to-metal structural thermal barrier. This pour and de-bridge method is suitable for withstanding demanding climates and conditions with high-performance requirements in terms of impact resistance, shear strength, and heat distortion.

Remarking on the capabilities of such systems, Mary Avery, vice president of marketing at Tubelite, explains, “In colder climates, this type of system provides superior energy results and condensation resistance using multiple thermal barriers, while providing structural integrity and aesthetic flexibility.” She continues, “Optimizing thermal performance helps lower the load on HVAC systems and reduces associated energy costs, while maintaining a comfortable interior temperature.” She also notes that the reduction of condensation can improve a building’s appearance and minimize moisture damage to adjacent building materials.

 

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Originally published in December 2020

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Academies
Creating High-Performance Building Facades
Buyer's Guide
Azo-Core Thermal Barrier
Azo-Core™ high-density foam thermal barrier by Azon for aluminum framing first made its debut in Europe. Thermal results of 0.25 U-value with double low-e insulating glass are achieved through actual testing. Beyond high thermal performance, Azo-Core maintains the structural aspects of the aluminum fenestration product.
Ultra-High-Performance Concrete Veneer Facades
Thin, lightweight facade panels made from natural stone and backed with ultra-high-performance concrete are bringing prefabrication for tightly jointed stone facades to another level. The panels are suited for complex three-dimensional geometries beyond current size or weight limitations. The ultra-thin, full-floor-height elements no longer require tower cranes, so floor space is maximized and durability is enhanced.
Hofmann Facades
www.hofmann-facades.com
601 Expansion Joint System
Inpro’s 601 hinged-wall expansion joint system can be infilled with glazing, metal panels, stone, brick, and more to disguise the exterior expansion joint. It is the ideal system for use on high-end exterior systems or conditions where the structural joint is located in a visible position on the building veneer.
Neolith® Calacatta Surface
Neolith®'s award-winning Calacatta surface is one of its most popular patterns, particularly for facades. Inspired by Italian Carrara marble, it delivers a sophisticated, luxurious, and urbane look to any building exterior. Lightweight, waterproof, highly resistant, sustainable, and low maintenance, architects are assured this material will stand the test of time.
Neolith®
www.neolith.com
Affordable Low-E, Low-Iron Glass System
Design an ambitious facade and realize it. Vitro Architectural Glass engineered the Solarban® Acuity low-e, low-iron glass system to combine the color fidelity of affordable Acuity low-iron glass—which is 60 percent less green than ordinary clear glass—with the performance that customers expect from the Solarban glass family.
Vitro Architectural Glass
www.vitroglazings.com