Design for life: The Role of Insulating Glass in Sustainable Buildings

By Helen Sanders

The most sustainable building is the one that is not built. It has no operational carbon footprint, and it takes no resources and emissions (embodied carbon) to construct. The next most sustainable building is the one that is renovated and repurposed. However, sometimes buildings must be built.

Insulating glass units (IGUs) are a key component of a building envelope. According to Mic Patterson of the Façade Tectonics Institute, through this adoption we have turned a material with a 1,000-year lifetime (single-pane glass) into one with a lifetime of 25 to 30 years. Embodied carbon has been traded off with reducing operational carbon emissions.

Since a 1,000-year IGU has yet to be invented, and since we need its operational energy efficiency, the immediate focus should be on maximizing the IGUs lifetime.

Material Selection and Design

Dual-seal polyisobutylene (PIB)/silicone systems are ubiquitous in commercial applications because of silicone’s water and UV resistance and structural strength. Because silicone does not provide a gas or vapor barrier, choosing a high-quality spacer is important since it has no back-up. Ensuring excellent adhesion between silicone and spacer is also crucial to preventing failures due to water pooling next to the PIB, spacer movement (for flexible systems), and over-extension of the PIB.

Quality & Climate Considerations

Manufacturing quality can be managed by choosing fabricators who make IGUs under certification programs such as the IGCC/IGMA and IGMAC programs. Contractors certified through the North American Contractor Certification program can help support installation quality.

The impact of climate stress can also be mitigated with application-specific edge seal analysis. Silicone contact width is always sized to prevent glass from falling off the building in structural glazing applications. Rarely is the silicone contact width sized to manage its strain, and the accompanying PIB elongation.

Water vapor and gas transmission increases with the cross-sectional area of the PIB and with shortened path length, both of which happen when the PIB is stretched. The more elongation, the higher the permeation, and higher risk of reduced service life. Small IGUs with thick lites, those with wide air gaps, or triple glazing are at highest risk for high edge loads. To support long service life, IGU configuration and silicone contact width should be designed routinely with a consideration of climate loads.

Helen Sanders is in strategic business development for Technoform North America Inc. in Twinsburg, Ohio. Read her blog each month at usglassmag.com/insights.

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