Fixing thermal bridging in masonry foundation walls

Cellular glass insulation has long been trusted in the roof of the Jardine water treatment plant.

Installing cellular glass structural insulating block

A particularly attractive feature of cellular glass is it presents no interruption during installation. Rather than installing additional courses of masonry, implementing a deeper foundation wall, or alternating between trades and materials, this material is simply laid in mortar as the first course of masonry. This course should butt the cellular glass block end-to-end with no mortar joint, to maintain thermal continuity. The blocks should be laid in the direction indicated (with facers on the top and bottom), so the cellular structure is oriented to support the maximum load and provide thermal resistance. No special tools are required for the mason to install the product as part of the process. However, efforts are underway to help support training and familiarity with the product for future installations.

As with all materials, there are specific requirements. As mentioned previously, the block must always be installed horizontally and is limited to one course. Bearing should be continuous across the surface, requiring solid masonry to be used at this location (although hollow units may be used in subsequent courses) and ensuring the veneer is not cantilevered off the surface. Due to very high compressive strength with no deflection, the material is not intended for flexural strength and must be continuously supported—taking care not to puncture or apply impact loads to the surface. For this reason, cellular glass block should not be left exposed. This can be addressed, as shown in the example details, by providing positive drainage to relieve hydrostatic pressure—a requirement not only for this product but as a best practice for below-grade waterproofing, insulation, structure, and any other material—and by protective flashing and counterflashing already typically integrated in foundation details to protect from ultraviolet (UV) and physical damage to any material in this location

As with all structural materials, bearing loads limit how tall and wide a building can be—often referenced using the American Society of Civil Engineers (ASCE) standard for verifications of these materials. Masonry veneer is limited in height, bearing on top of the cellular glass material, based upon the designer’s calculations considering live and dead loads, and generally limited to three or less stories—approximately 11 m (37 ft) in Canada. As this is project-specific, it is critical for the engineer to be included at the earliest point in the design process for accurate integration.

Previous projects across the pond

Cellular glass insulation has a successful history in Europe, where it was specified in three different sizes to match the width of the masonry walls in which insulation was installed—100 mm (3.9 in.), 140 mm (5.5 in.), and 215 mm (8.4 in.). This product was used for foundation applications and for separation of conditioned spaces. This was determined appropriate through more engineering by designers according to Europe’s prevailing building codes.

Moving forward with continuity

As the design and construction community in North America becomes more familiar with the use of cellular glass structural insulating block, it is anticipated more testing and analysis will be developed for use in additional locations to address thermal bridges—much like Europe. As many codes and standards vary from continent to continent, this integration will take time.

As designers strive to improve comfort, reduce energy use, and achieve performance which goes beyond code, addressing thermal bridges presents a path forward. Improving on the benefits brought about by ci and air barriers in buildings is an opportunity to further reduce their energy use. Many North American designers and installers are at the forefront, leading the way in discovering how cellular glass insulation can be deployed in new applications and how to close in on the performance gap.

Author’s note: The article was based on a study in Alaska using U.S. codes, but considering implications based on Canadian building codes.

Notes

1 See “The Critical Role of Buildings: Perspectives for the Clean Energy Transition,” published by International Energy Agency, April 2019. For more information, visit https://www.iea.org/reports/the-critical-role-of-buildings.

2 Consult “A Review of the Energy Performance Gap and Its Underlying Causes in Non-Domestic Buildings,” by Chris van Dronkelaar, Mark Dowson, E. Burman, Catalina Spataru, and Dejan Mumovic, published in Frontiers in Mechanical Engineering, 1, 2016. For more information, visit www.frontiersin.org/article/10.3389/fmech.2015.00017.

Author

Tiffany Coppock, AIA, NCARB, CSI, CDT, LEED AP, ASTM, RCI, EDAC, is the commercial building systems specialist at Owens Corning.

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