The following piece is an excerpt from the report, Embodied Carbon: A Clearer View of Emissions.
Overview
When architects and engineers consider the environmental impacts of building enclosures, we typically think about reducing operational impacts through more efficient building envelopes. Efficient envelopes are essential to carbon reduction goals, however, they are also responsible for significant embodied or “upfront” carbon—emissions that come from extracting, manufacturing, and transporting building materials. Common enclosure materials such as glass and aluminum are significant sources of emissions. The construction industry must reduce near-term carbon emissions to meet the goals of the Paris Agreement. To achieve this, we must reduce both operational and embodied carbon.
Measuring Carbon
The terms “embodied carbon” and “global warming potential” are often used interchangeably. We measure total global warming potential (GWP) because it includes other greenhouse gases in addition to CO2. Because other greenhouse gases have different levels of global warming potential, overall GWP is measured in kg CO2e or kilograms of CO2 equivalents.
New Tools
Several new tools have become available recently that help designers consider upfront environmental impacts when specifying building enclosure products. Walter P Moore utilizes multiple LCA (life cycle assessment) tools, including Tally (a plugin for Revit) and The Athena Impact Estimator, as well as the Embodied Carbon in Construction Calculator (EC3) tool, which focuses on material procurement.
A recent LCA for a Walter P Moore project further illustrates how these tools better inform design decisions. Team members utilized Tally to analyze two common opaque cladding systems—aluminum composite material (ACM) panels and aluminum plate panels—as well as several insulation options for the metal stud backup wall supporting the cladding.
Thermal Bridging
When designing a wall buildup, it is important to consider thermal bridging to determine how much insulation is needed. In our project example, the backup wall in options 1 and 2 used mineral wool continuous insulation on the exterior of the wall to avoid thermal bridging through the studs while options 3 and 4 used spray foam insulation in the stud cavity as well as a thinner layer of mineral wool continuous insulation on the exterior. The LCA study illuminates the fact that the material with the greatest global warming potential is spray foam insulation using an HFC (hydrofluorocarbon) blowing agent.
However, spray foam can be installed using different blowing agents. Performing an LCA allows the designer to assess the impact of switching to a spray foam product that uses HFO (hydrofluoroolefin) as a blowing agent, showing a significant impact reduction, bringing the global warming potential of wall options 3 and 4 much closer to options 1 and 2 (see graphic, above).
Continuous Insulation
Where there is adequate space for a thicker wall buildup, continuous insulation may be a better choice as it reduces thermal bridging, thus reducing the overall amount of insulation material required and producing better envelope performance and lower global warming potential.
The ACM panels have a lower global warming potential than aluminum plate panels due to lower weight and less aluminum needed in the panels. However, they have higher impacts in other categories such as acidification and eutrophication potential.
Information about the upfront environmental impacts of building materials is becoming more accessible, empowering architects and engineers to use data to make better choices during design. These analyses allow teams to have more robust discussions with owners, find hot spots within systems, and achieve the reductions in upfront impacts essential to meeting climate goals.
