The Role of Insulation in Mission-Critical Design

Improve moisture control and fire performance with the right material
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Sponsored by Owens Corning
By Jeanette Fitzgerald Pitts

Cellular Glass

Cellular glass insulation is a lightweight, rigid insulation that is known for its durability, moisture resistance, and the non-toxic elements it contains. The primary ingredients in cellular glass are recycled glass, sand, and other glass batch ingredients, which are combined and then melted. This mixture is ground and mixed with a cellulating agent, then heated again. CO2 is used as the blowing agent, which creates the cellular structure in the material that makes it an insulator.

Cellular glass has a closed-cell structure, which means that the material is filled with cells that are self-contained within their own walls and maintain their own shape. A closed-cell structure offers greater insulation value and better moisture resistance than the alternative open-cell structure, allowing this material to be air and watertight.

Recent innovations in manufacturing have allowed cellular glass to reach an R-value of R-4 per inch, giving it an insulating power that is on par with many of the rigid foam plastic insulations while delivering a superior moisture resistance and compressive strength.

One of the reasons cellular glass offers such an incredible resistance to moisture is the way it is installed. Cellular glass is usually installed by embedding and sealing in a liquid adhesive, such as hot rubberized asphalt, and is then covered with the roof membrane such as a built-up roof (BUR) assembly. Beyond the roof, design teams today are specifying cellular glass into the walls, floors, perimeter, and under slab in a wide variety of commercial and industrial projects.

Cellular glass also supports sustainable design goals in many important ways. It is manufactured using more than 60 percent recycled glass. Beyond the impressive amount of recycled content contained within cellular glass, this inorganic material contains no ozone-depleting propellants, flame retardants, or binders and is free of volatile organic compounds (VOCs). Another green aspect of cellular glass is that zero waste is sent to the landfill during the manufacture of this material.

Matching Insulation Solutions with Mission-Critical Needs

Mission-critical buildings have special needs. They are structures that cannot fail. They have operations that cannot be interrupted. The right insulation can offer the optimal mix of performance characteristics to help safeguard the interior from extreme events, and the typical ones like aging components, leaking, and use. For example, roofs with heavy overburden can benefit from insulation with a high compressive strength, water impermeability, and durability. Insulation selected for exterior walls behind combustible claddings should exhibit superior fire performance and be resistant to incidental moisture in the wall cavity. Let’s take a closer look at the various needs of a mission-critical envelope and the insulating materials that are best equipped to meet them.

High-profile buildings such as One World Trade Center have been constructed using mineral wool perimeter fire-containment system products that are Safety Act designated.

Moisture Resistance

Unfortunately, building materials located within the building envelope will at some point encounter water in the form of either rain, snow, or ice. While some materials are only briefly exposed during construction, others are left to encounter intermittent moisture throughout the life of the building, as is the case for continuous insulation in the exterior wall cavity. Other materials are exposed to more moisture pressure when placed on a horizontal roof surface or below grade.

According to a study of Zurich insurance companies, the number-one insurance claim filed for construction defects is water intrusion. Common moisture management weaknesses in the envelope include rain or groundwater leaking through the roof, walls, windows, or foundation; the infiltration of water vapor through the building envelope during warm, humid weather; or the exfiltration of humidified air from the interior to the exterior in dry winter climates.

These moisture problems can have significant and negative effects on the efficiency, safety, and health of the interior environment. Moisture can degrade the performance of the thermal insulation and even damage the insulation material. It can cause the deterioration and failure of roofing and flooring adhesives and damage wood, brick, concrete, and metal building materials. Damp conditions can also result in the proliferation of molds, mildews, and bacteria, which can threaten the indoor air quality of the interior space. All of these issues can be especially problematic in a mission-critical building that cannot be contaminated or afford the exposure or the downtime to correct them. Selecting an insulation with greater degrees of moisture resistance can help to equip the envelope to perform as needed in these sensitive interiors.

Mineral wool continuous insulation has been engineered to be hydrophobic, which means that it is highly resistant to liquid water absorbing into the surface. However, should the material ever absorb moisture, its resiliency is demonstrated by how quickly it drains and reliably returns to its previous thermal properties.

For environments with heavier moisture exposure such as low-slope roofs, cellular glass is impervious to liquid water due to its closed-cell structure. Because it is watertight, cellular glass, when combined with watertight adhesives, may be installed with the actual roofing membrane to introduce multiple waterproofing layers into the assembly. One advantage to this design redundancy is that when the roof membrane reaches the end of its life or needs to be repaired, the cellular glass insulation, if incorporated into an assembly designed for removal and replacement of the roof membrane, may be left intact and prevent disruption to the critical functions of the building during repair or replacement.

 

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Originally published in Architectural Record

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