GLOBAL TECHNOLOGIES AND TRENDS GAINING TRACTION
baseline design. WBLCA can help designers understand where the embodied carbon hotspots are in their design and where there are opportunities for reduction. While there are many ways to reduce the embodied carbon in a building project, the façade is an untapped component as it lies at the intersection of several strategies for reduction of building industry carbon emissions. Well-designed high-performance facades can lead to reduced energy use through thermal efficiency and by balancing shading with daylighting, depending on climate zone and time of year. However, many common façade materials are highly carbon intensive to produce. Being more intentional about where and how to use them can hold the key to optimization. A Closer Look at the Impacts of Façade Materials To illustrate the effects of façade design choices on embodied carbon, we have completed several design exercises to assess the embodied carbon of various wall assemblies per square foot of façade area. In an assessment of opaque wall assemblies prepared for Walter P Moore’s Stewardship Report Embodied Carbon: A Clearer View of Carbon Emissions, we found that insulation and cladding choices can make a big difference in the embodied carbon of a wall assembly. Our next step was to look at glazing assemblies. We used Tally, a life cycle assessment (LCA) tool for Revit, to assess three different options for a 20-foot-high atrium curtainwall. We wanted to understand how three different mullion strategies would impact the embodied carbon of the overall wall. The first strategy we looked at was to minimize the size of the aluminum mullion by using a secondary steel hollow structural section tube at mid-span. The second strategy was to use a steel reinforced mullion to achieve the span, and the third option was to use a deep aluminum mullion with no reinforcing that was also capable of achieving the desired span. Our goal was to find out how much of an impact do these structural and aesthetic choices have on embodied carbon. In this design exercise, we found that the deep mullion option had the lowest embodied carbon. However, a deep mullion is not 86
OPTION 1: 6” Mullion, no reinforcing HSS 6x6x3/8 supporng at mid span 3 transoms at 6” depth
OPTION 2: 8” Mullion with steel reinforcing 3 transoms at 6” depth
always favored by designers who want to minimize the depth of the system. The next best option, in this case, is to use secondary steel to break up the span and enable the use of a smaller mullion. The steel reinforced mullion had the highest impact of the three options we studied, with embodied carbon approximately 20% higher per square foot. Once multiplied across an entire façade, this can make a significant difference in a building’s overall embodied carbon. It could be the difference that enables the project to get a LEED point for environmental impact reduction. It is important to note that each project is unique, and these results are specific to the conditions studied in this design exercise. This highlights the importance of using LCA to assess the embodied carbon impact of the design decisions that result from each project's unique conditions.
intelligent glass solutions | summer 2021
OPTION 3: 10” Mullion, unreinforced 3 transoms at 6” depth
Diving deeper into each assembly, we can identify carbon hotspots and understand how much embodied carbon each component of a glazing assembly is responsible for. Looking at the curtainwall only from the first strategy, we wanted to find out the embodied carbon contributions of the insulating glass units (IGU), aluminum, and steel, normalized per square foot of façade area. In this example, the glass is the biggest contributor to embodied carbon; however, the aluminum has carbon impact disproportionate to its share of the mass of the system. It represents 21% of the mass of the system but is responsible for 32% of the embodied carbon. As a result, reducing aluminum quantities may be a good place to start in order to reduce the overall embodied carbon of this system. This design exercise provides one example of how embodied carbon can be considered as a metric, balanced with aesthetic concern and cost.