Words: Tiffany Coppock, AIA, NCARB, CSI, CDT, LEED AP, ASTM, RCI, EDAC, Commercial Building Systems Specialist at Owens Corning
Photos: Owens Corning, stevegeer
Masonry construction has long been valued in America’s mission critical buildings for its inherent durability, redundant properties, compressive strength, heat/moisture/vapor resistance and ecological profile. Now, cellular glass insulation is reintroducing these same qualities to the rooftops of mission critical commercial buildings. In June at the “AIA Conference on Architecture 2019” in Las Vegas, Owens Corning announced FOAMGLAS® cellular glass rigid board insulation is returning to America.
What defines a “mission critical” building? While every building has a mission, the potential cost of a disruption can inflict may be devastating in a building deemed “mission critical”. Viewed through this lens, a mission critical building might be a data center, critical care hospital, or a national security facility. Even a casino could be considered mission critical, given the amount of hourly revenue at stake. For example, when Typhoon Mangkhut struck Macau near Hong Kong in 2018, Bloomberg reported the thirty-three–hour shutdown of the world’s biggest gambling hub cost operators as much as $186 million in revenue1.
Chapter 16 of the International Building Code provides some objective guidance for designating mission critical buildings. Table 1604.5 specifies “Risk Category of Buildings” and classifies the various code-defined occupancies contained in buildings. Structures that provide critical communications or functions essential to public welfare, such as water filtration plants and utilities, as well as hospitals, are categorized as buildings that require additional factors to make them more durable and damage resistant. Because strength and redundant protection are key to long term durability, it should come as no surprise that many of these buildings are commonly constructed with masonry. The same high-performance and endurance properties that make masonry ideal for enclosures also apply to cellular glass rigid insulation. What makes this material unique, and why is the longstanding material returning to the U.S. commercial roofing market after a long absence?
A Unique Chemistry Supports Strength and Stability
The primary reason cellular glass performs so well from a strength, stability, moisture and heat resistance perspective is simply that it is glass. Cellular glass insulation rigid board is produced using sand as the primary ingredient, along with other ingredients including limestone and soda ash. The ingredients are melted into a molten glass. When cooled, the mullet glass – called cullet – is mixed with carbon black and crushed into a fine powder which is heated in an oven creating a chemical reaction. This reaction results in a glass matrix that foams or “bubbles up” during the process, resulting in a product comprised of millions of completely sealed glass cell bubbles. ASTM C552, Standard Specification for Cellular Glass Thermal Insulation, provides an overview of the essential physical property requirements of cellular glass insulation. The ingredients and the process that creates cellular glass allow the material to offer some powerful performance benefits unmatched by other roofing materials.
A Proven Material for Performance and Endurance
Developed in Europe more than seventy years ago, cellular glass has an interesting history and has been part of high performing buildings in Europe for decades, where longstanding performance is a key priority. In the U.S., the vapor resistance, compressive strength, and dimensional stability of cellular glass made it popular for industrial applications. During the 1960s through the mid 1980s, cellular glass was widely used in commercial building roofs. In fact, there are thousands of existing assemblies listed in RoofNav, the Factory Mutual Research Corporation public database, that include rigid cellular glass used in conjunction with a variety of membranes.
The introduction of new roofing material options in the late 1980s led to a market shift in the U.S. toward less expensive insulating materials for commercial roofs. However, as the mission critical marketplace looks for insulating materials that deliver the “gold standard” when it comes to commercial roofing applications for mission critical roofs, cellular glass offers unmatched performance across a number of categories.
Ultimately, specifiers must focus on using the best solution to meet the needs of a project. Several of the performance attributes that make FOAMGLAS® well suited for mission critical roofing applications are noted below:
Redundancy: Reliability is non-negotiable in mission critical buildings. Redundancy supports reliability by duplicating critical components in a system, typically in the form of a back-up material or mechanism. In commercial roofing applications, cellular glass provides a back-up layer of watertight protection to help protect a facility in the event a leak occurs in the roofing membrane. Cellular glass is typically adhered to roof decks with asphalt or cold adhesive, and joints are also sealed with the same material to create the redundant waterproof layer. And, unlike foam plastic, cellular glass tolerates solvents and bitumen that may be present in the roofing system. These characteristics allow cellular glass to effectively act as a secondary waterproofing membrane, creating the building’s redundant roof systems.
Compressive strength: The highest levels of compressive strength available with foam plastics are merely the starting point for cellular glass insulation. The high compressive strength of cellular glass allows the material to support high loads without deflection or movement, and without compressive creep even under sustained load. This ability to tolerate heavy loads, plus the redundancy of a secondary waterproofing layer, makes cellular glass a good choice for rooftop plazas exposed to vehicular or pedestrian traffic. Some examples include plazas or rooftop parking decks, as well as rooftop equipment such as HVAC, communications equipment or solar arrays that are costly to move for membrane repairs. Cellular glass can also be tapered and is easy to cut/handle on the jobsite.
Resists acid and chemicals: Rooftops can be hostile environments for roofing membranes. The inert composition of cellular glass allows it to tolerate chemically aggressive agents and harsh conditions. The James W. Jardine Water Filtration Plant located next to Chicago’s Navy Pier provides a good example of cellular glass insulation’s ability to withstand chemical and environmental elements. Five years ago, the plant’s fifty-year-old structural deck and graveled coal tar pitch roof was replaced with a new thermoplastic single ply roofing membrane including more than 712,000 board feet of highly stable, chemical and moisture resistant cellular glass insulation. The new cellular glass roof insulation will provide the roofing membrane a highly stable base, even in Chicago’s extremely variable weather conditions. It is also vapor impervious and able to withstand exposure to chemical agents in the plant, and any leaking of acidic deposits of bird flocks that congregate on the rooftop. A second water purification plant in Chicago is being re-roofed in a similar manner.
Impervious to moisture: Just as a glass container will not permit water to escape, the glass bubble composition of cellular glass insulation provides a barrier against water intrusion. FOAMGLAS® insulation is both water and vapor resistant and provides an all-glass closed-cell insulation structure retaining all the water–resistant properties of glass. Each glass bubble or cell is hermetically sealed during the manufacturing process, ensuring that FOAMGLAS® insulation is totally impervious to water vapor and to other gases.
Ecologically responsible: The material composition of cellular glass can help support sustainability objectives. Cellular glass is an inorganic material and contains no blowing agents with high global warming potential, flame retardants, or binders. Its trim materials are re-used in the manufacturing process. Finally, cellular glass does not support the growth of microorganisms or bacteria, and is not subject to rotting or vermin infestation.
Delivering value below the rooftop: The benefits of cellular glass insulation extend beyond the rooftop, even to the foundation of a building. The high compressive strength of cellular glass insulation coupled with zero deflection under load, along with its R-value, makes it useful for eliminating thermal bridging through masonry walls where the load path through the masonry must cross over the continuous insulation (ci) path in the wall assemblies such as at parapets (Figure1).
The performance benefits cellular glass brings to the walls of the enclosure also extend to below-grade areas in the building’s foundation. For example, brick veneer on a bearing ledge has long been accepted as a necessary thermal bridge to accommodate load resolution into the structure’s foundation. Without a structural insulation, it is not possible for the ci path and the load resolution path to cross in the enclosure. The load path must always take priority. Cellular glass solves this challenge and provides a structural solution to permit the ci path to cross over the load resolution path. Figure 2 illustrates cellular glass insulation crossing the load resolution path, thus connecting the ci path to provide uninterrupted insulation. As it does so, the approach avoids a thermal bridge from occurring between the brick veneer and the building foundation.
In addition to providing strength for weight bearing purposes, unlike concrete, cellular glass delivers the required R-value to meet insulating needs and provides an efficient means of interrupting the thermal bridge in the enclosure walls.
While most of the large opportunities to recoup thermal bridging have been tapped by today’s building science technologies, small micro-efficiencies such as minimizing thermal bridging present an opportunity to optimize energy performance in the building enclosure. Improvements such as the use of cellular glass in select enclosure and foundation applications can complement and enhance the energy saving benefits of other thermal innovations.
In a tight labor market, an important factor when considering materials will always be ease of use on the job site. Cellular glass insulation requires no special training to install, is easily cut and may be installed using methods familiar to contractors such as mechanical attachment, or adhering with hot asphalt, cold applied asphalt adhesives, or two-part polyurethane adhesives.
Evaluating Cost vs. Benefits
When does it make sense to choose cellular foam glass to help protect the commercial roof membrane? As noted earlier, mission critical buildings cannot be allowed to fail. Some processes and treasures are truly irreplaceable. For example, an archivist shared with this article’s author that the archive housed original documents developed in the founding of the United States of America. Even the best insurance policy cannot provide protection enough to guard against the loss of such treasures. For stable, water resistant, vapor impervious, non-combustible applications, cellular glass is an ideal commercial roof insulation material.
Of course, similar to masonry, cellular glass insulation is chosen based on its performance benefits and not based on low-cost, especially when compared to foam plastics. However, if an architect specifies materials with a mindset to add value and deliver redundancy in the mission critical environment, cellular glass can boost confidence in the material’s enduring performance. And over the long run, cellular glass can contribute to the overall value of a project. For example, cellular glass can replace other layers in the construction system such as vapor retarders, moisture barriers, and radon-control components. It may also enhance longevity of the roofing membrane and support environmental benefits desired by building owners, occupants, and third-party environmental certification organizations. Installed under load bearing concrete slab applications, the high compressive strength and zero deflection under load properties of cellular glass could even present an option to install a thinner or more lightly reinforced concrete slab.
Yet another factor that should be considered are the challenges that may be associated with replacing a roof in the future. Gaining access to tear off and replace a high–rise roof in Manhattan, a very dense urban environment, can present extreme logistical challenges when replacement is required. Designed to endure for decade after decade, cellular glass insulation provides a highly stable and durable base to support a high–quality roofing membrane, and a long-standing approach to reliable performance.
For American architects designing mission critical rooftops, cellular glass rigid insulation makes it possible to achieve performance objectives and complete buildings with confidence.