{"id":29260,"date":"2017-03-08T10:19:52","date_gmt":"2017-03-08T15:19:52","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=29260"},"modified":"2017-03-03T15:54:53","modified_gmt":"2017-03-03T20:54:53","slug":"designing-spandrel-glass","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/designing-spandrel-glass\/","title":{"rendered":"Designing spandrel glass"},"content":{"rendered":"
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Photo \u00a9 Jason Ness. Photo courtesy ICD High Performance Coatings<\/figcaption><\/figure>\n

by Steven D. Marino
\n<\/strong>Among the many reasons architects specify glass are its beauty and versatility. In addition to offering the full spectrum of transparency, color, and high environmental performance as vision glass components, this material can be opacified in spandrels to create visual flair on building fa\u00e7ades while hiding unsightly interior features such as hung ceilings, knee-wall areas, between-floor voids, mechanical equipment, wires, vents, and slab ends. Although glass spandrels have been popular on building fa\u00e7ades for decades, there are technical factors design professionals must account for when specifying these assemblies.<\/p>\n

Through the application of coatings, film, or other materials to the indoor surface of a glass lite, glass spandrels block light and prevent transparency. In monolithic and insulating glass unit (IGU) spandrels\u2014the two most common types\u2014ceramic enamel frits, silicone-based paints, and plastic or metal films are affixed to or installed just behind the glass substrate to make it opaque.<\/p>\n

Shadow box spandrels are a third alternative. Unlike the aforementioned conventional spandrels, these assemblies incorporate transparent glass and unite it with a separate insulating component. In most cases, this component is a rigid foil-backed material, taped to the surrounding framing system to prevent the passage of light.<\/p>\n

Although monolithic and IGU spandrels are typically specified to enhance the building\u2019s appearance, it is usually impossible to create a seamless color match between spandrel glass and vision glass on a fa\u00e7ade with these types of units. However, because they can be fabricated with an almost limitless palette of opacifier colors, monolithic and IGU spandrels are ideal for complementing vision glass and other building finishes such as metal, brick, concrete, and stone.<\/p>\n

If a strong color match between vision glass and spandrel glass is desired on a building exterior, using shadow box spandrels is recommended.<\/p>\n

Monolithic glass spandrels
\n<\/strong>Monolithic glass spandrels are the most basic spandrel variety, consisting of a coated or uncoated glass substrate to which an opacifier is applied, as seen in Figure 1.<\/p>\n

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Monolithic spandrels feature light-blocking materials such as ceramic enamel frits, silicone-based paints, or plastic or metal films affixed to a single pane. This material is applied to a surface facing indoors (Surface 2 in Figure 2). <\/span>
Images courtesy Vitro Architectural Glass<\/span><\/em><\/figcaption><\/figure>\n

Most manufacturers recommend all glass specified for monolithic spandrels be heat-strengthened to provide the mechanical strength needed to resist wind load and thermal stresses. The inherent break pattern of heat-strengthened glass is another reason for this recommendation, as broken heat-strengthened glass is much more likely than annealed (i.e. <\/em>non-heat-treated) or fully tempered glass to remain in place until it can be replaced.<\/p>\n

Whether heat-strengthened or fully tempered, heat-treated glass products are produced in a similar fashion and using the same processing equipment. The glass is heated to approximately 650 C (1200 F), then force-cooled to create surface and edge compression. The cooling rate of the glass determines if it is heat-strengthened or fully tempered\u2014to produce the latter, cooling is much more rapid, creating higher compression; for the former, cooling is slower, resulting in a compression lower than fully tempered glass, but higher than annealed.<\/p>\n

As indicated in Figure 1, insulation is often used in conjunction with spandrel glass. When the insulation is to be applied directly to the opacified surface of the spandrel glass, it is important to work with a glass spandrel fabricator, as well as the adhesive and insulation suppliers, to ensure these products are compatible with the opacifying material. These suppliers can also recommend the best installation procedures for ensuring long-term performance and appearance.<\/p>\n

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Insulating glass unit (IGU) spandrels are fabricated with two panes of glass to improve a building’s insulation and energy efficiency. Opacifier (light-blocking) material is typically applied to Surface 2, Surface 3, or Surface 4 of the unit.<\/span><\/figcaption><\/figure>\n

Insulating glass unit spandrels
\n<\/strong>IGU spandrels are fabricated with an opacifying material applied to the third or fourth surface of the indoor glass lite, labeled 3 and 4 in Figure 2.<\/p>\n

As these types of spandrels are designed to function like conventional IGUs, with the goal of improving a building\u2019s energy efficiency, they are commonly specified with low-emissivity (low-e) coatings.<\/p>\n

When this is the case, specifiers must give special consideration to which surface locations of the IGU are specified for the low-e coating and the opacifier because of the potential these materials have for elevating temperatures within the assembly. For IGU spandrels with low-e glass, the recommended location for the opacifying material is the indoor surface of the indoor lite of glass (Surface 4 in Figure 2).<\/p>\n

Another design alternative is to place the low-e coating on Surface 2 of the IGU and the opacifier on Surface 3. As the low-e coating, opacifier, and sealants occupy the same space in this type of spandrel assembly, it is critical to confirm their compatibility with their respective manufacturers.<\/p>\n

In some instances, it is possible for an improper combination of materials in the IGU air space to produce volatile organic compounds (VOCs), which can then condense on the low-e coating and cause it to degrade, voiding any applicable warranty.<\/p>\n

Precautions should also be taken with spandrel assemblies combining low-e coatings and medium- to dark-colored opacifier coatings. Depending on their location and orientation to sunlight, it is possible for these spandrel designs to generate exceedingly high glass temperatures that can expose the assembly\u2019s interior lite to potentially destructive levels of thermal stress.<\/p>\n

Proper design will mitigate the potential for excess concentration of solar heat within the spandrel assembly. The location of the insulating material can be adjusted, and suitable levels of air circulation behind the IGU enabled.<\/p>\n

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Spandrels create a pleasing geometry on the facade of the Louisa, a 16-story apartment building in Portland, Oregon. <\/span>
Photo \u00a9 Kris Vockler. Photo courtesy ICD High Performance Coatings<\/span><\/em><\/figcaption><\/figure>\n

As with monolithic glass spandrels, using heat-strengthened glass for both of the lites in the IGU is recommended. Additionally, if the outdoor glass lite of any vision unit on a building fa\u00e7ade is tinted, the outdoor lite of any adjacent spandrel units should be the same tint, and a neutral-color opacifier should be specified for Surface 3 of the indoor lite. Doing so is primarily for appearance, although it is important to note tinted glass can contribute to a thermal stress risk because of its increased solar absorption. For this reason, it usually requires heat-treatment.<\/p>\n

Insulation and glass recommendations
\n<\/strong>As the name suggests, insulating materials are typically used in spandrel IGUs. Depending on the glass type and the recommendation of the spandrel fabricator, insulation may be applied directly to or positioned 25 to 50 mm (1 to 2 in.) from the glass surface.<\/p>\n

Similar to monolithic glass spandrels, if the insulation material is to be applied directly to the glass surface, specific recommendations regarding its compatibility with the glass, sealants, and other materials inside the spandrel IGU should be solicited from the participating suppliers.<\/p>\n

Given that insulation is typically designed to trap and potentially enable solar heat buildup, design professionals should consider using fully tempered glass for the interior lite of the spandrel IGU. This reduces the probability of thermal stress-related breakage, and even if breakage does occur, the exterior layer should prevent fall-out. However, fully tempered glass should not be used for the exterior ply of an IGU unless mandated by code, because of the fall-out potential if it breaks. As always, heat-strengthened glass is recommended for the exterior lites of these units.<\/p>\n

Shadow box spandrels
\n<\/strong>Shadow box spandrels are typically specified for applications where achieving a color match between the vison glass and spandrel glass on a building fa\u00e7ade is desired.<\/p>\n

As shown in Figure 3, a shadow box spandrel will typically incorporate:<\/p>\n