Optimizing Carbon Emissions in Insulating Glass and Aluminum Frames

Buildings are responsible for a staggering 39% of worldwide carbon emissions – from both building operations (28%) and building construction (11%). At a recent Façade Tectonics Institute (FTI) forum in Los Angeles, members of the FTI carbon working group provided insights into the biggest levers for reducing carbon emissions related to fenestration. These insights are important because it focuses action on the most impactful strategies.

Embodied Carbon vs. Operational Carbon

Recognizing the dual impact of embodied and operational carbon emissions is vital as trade-offs between the two forms are often required.

Embodied carbon represents the carbon emissions generated during the construction process, including the manufacture of building materials. Operational carbon accounts for emissions incurred during a building’s use.

Insulating Glass and Carbon Emissions

Insulating glass units (IGUs) are fundamental components of modern building envelopes, providing thermal insulation, solar control and daylighting, reducing a building’s operational carbon. Yet flat glass is a carbon intensive product to make because of the high-temperature gas-fired float glass process. Emissions from making flat glass comprise 75% or more of the total embodied carbon of an IGU.

The biggest theoretical levers for reducing the embodied carbon for flat glass are renewable fuel and high quantities of post-consumer recycled content. While there is progress in these areas, the technical barriers are high to rapid supply chain transformation. Currently, the most impactful levers for minimizing embodied carbon are:

Design: The number of glass panes and their thickness determine an IGU’s embodied carbon, as well as quantity used. However, this is not a window-to-wall-ratio trade-off since opaque walls can also have high embodied carbon. Whole life carbon assessments are critical to understanding the balance between operational carbon improvements and embodied carbon investment for triple pane glazing. IGU lite thicknesses are based on the strength requirements of the largest unit. This configuration is then replicated throughout the building, irrespective of size. Designs with many unique sizes increase glass waste at the manufacturer. Both strategies increase embodied carbon.

Durability: Investing in IGU durability is critical to preserving the carbon investment in flat glass. While the edge seal material’s impact on emissions is minimal (around 5%), material choices and quantities significantly affect the IGU’s lifetime and should be specified wisely.

Aluminum Frames and Carbon Emissions

While it is challenging to move the needle on embodied carbon in glass, for aluminum there are easier levers:

Energy Sources: Carbon emissions from the smelting of alumina depend on the electricity grid energy source. Smelting processes using hydropower results in significantly lower carbon emissions. Aluminum sourced from regions with gas and coal-powered grids, such as China and the Middle East, has a higher embodied carbon.

Recycled Content: Increasing recycled content of aluminum reduces its embodied carbon. However, this must be balanced with the availability of recycled aluminum and the impact on surface finish quality.

Integrating complex thermal barriers into aluminum frames improves building operational carbon, adding approximately 10% to the embodied carbon of aluminum extrusions. Typically, this is a wise investment.