Low-Carbon Cladding and Shading Design

In the last few years, the design community has embraced the challenge of reducing embodied carbon in buildings. Several tools are now available for comparing materials and assemblies in the structure and enclosure from the standpoint of product-stage greenhouse gas emissions. However, most tools do not provide sufficient information for designers to be able to compare façade cladding and exterior shading materials and assemblies – two pieces where architects have the most control in terms of product selection. Authors of this paper at Atelier Ten identified this as a research gap, and performed embodied carbon-focused comparisons of material alternates for these applications across several large-scale commercial construction projects in the Bay Area.

Material options included terracotta, aluminum extrusions, cementitious composites like fiber-cement, ‘extruded' glass-fiber reinforced concrete (GFRC) and ultra-high performance concrete (UHPC), fiber-reinforced plastic, and wood. Environmental impact data for these was obtained from a combination of product-specific Environmental Product Declarations (EPDs), industry-wide EPDs, LCA studies published in academic journals, and data from manufacturers. Cementitious composites like UHPC were found to be the option with lowest embodied carbon for both cladding and shading applications.

Furthermore, noting that the enclosure can make up 20-30% of the total embodied carbon of a building, with about half of that coming from aluminum, the authors studied the embodied carbon origins of aluminum. Aluminum extrusion’s embodied carbon is high variable, being dependent on its sourcing location’s electricity grid mix, the proportion of primary and secondary billet, and its finish coating. Designers are recommended to specify aluminum from hydro-powered grid regions, with high recycled content and anodized finishes. Manufacturers are recommended to provide 'green' product lines for project teams are seeking sustainable aluminum, while the industry works towards reducing GHG emissions as a whole.

Finally, exterior shading was evaluated from the lens of a 'carbon investment'. The authors found that even in conservative scenarios, performative shading would 'pay back' its initial embodied carbon through operational carbon savings in less than 5 years - making it a sound design choice for most US projects.