by Claire McConnell and Sean Cryan
Linking Research, Development, and Projects
Mithun’s commitment to reducing carbon emissions in the built environment is a key tenet of our integrated design practice, informing project approach, firm culture and advocacy efforts. Increasingly, research and development plays a valuable role in advancing evidence-based decision making in our work, transforming projects and design through meaningful inquiry and exploration. This iterative cycle of discovery and application accelerates design for positive change.
In 2004, while creating a sustainable development framework for Lloyd Crossing in Portland, Oregon, the one component not readily available for analysis was the embodied carbon related to construction. This gap inspired Mithun’s development of the free, online Build Carbon Neutral (BCN) calculator to offer high-level insight into the embodied carbon impacts of early design decisions. Widely referenced for 15 years, the BCN calculator is now being updated to incorporate advanced structural, architectural and site design factors, synthesizing what we as a practice and an industry have learned since its release in 2007.
A more recent R+D project, Embodying Change, marked Mithun’s deep dive into embodied carbon through study of the application of Life Cycle Assessment (LCA) software and methods to our design workflows across multiple scales and project types. This effort provided a running start in integrating embodied carbon accounting into our design process, including the development of an internal project database to track performance across our design portfolio. We have benchmarked more than 15 projects over the past year that are below the 500 kg CO2e/m2 emissions limit set by the International Living Future Institute in its Zero Carbon certification. One-third of these projects have a global warming potential (GWP) of less than 350 kg CO2e/m2.
As we continue to learn how to design for a low embodied carbon footprint, this database enables us to identify trends across our portfolio, translate lessons learned across projects and develop best practices, in addition to encouraging further investigation into low carbon design strategies. This study built capacity at Mithun for the easy incorporation of LCA into design phases on specific projects.
For The Bush School, the owner, architect and contractor collaborated to find a structural solution that provided embodied carbon performance in parallel with conventional criteria such as constructability, schedule and overall cost. Throughout the design process, the team used targeted studies of early structural options and whole-building LCA to engage in discussion about the merits of each system in meeting carbon goals. The project landed on an efficient hybrid structure using wood, steel and concrete. The design combines a concrete basement level with light-gauge steel framing topped by two levels of mass plywood floor construction to reduce embodied carbon and optimize efficiency. This hybrid approach served to reduce embodied carbon by 50% compared to the initial design. The final calculated GWP is 227 kg CO2e/m2.
Innovating LCA Practice, Inside and Out
Our use of LCA in design started with architectural design, but these efforts have also helped identify gaps in our knowledge and design-thinking around carbon. As an integrated design firm, Mithun aims to understand embodied carbon impacts across architecture, interior design, landscape architecture, urban design and planning.
Interior Design: We are actively working to understand the embodied carbon trends in our interiors work and the relative impacts of finish materials, casework and furnishings. Over the past year, we have benchmarked three of our recent tenant improvement (TI) projects, including our own Seattle office, with a GWP range of 25-50 kg CO2e/m2. A roadmap for carbon reduction in interiors is critical. Embodied carbon impacts of TI work aggregate over time with tenant turnover or refurbishment; by providing low-carbon design standards to our clients we can achieve carbon reductions at scale.
Landscape Design: In a recent study benchmarking embodied carbon in an industrial warehouse facility, we found site hardscape contributed 25% of the overall carbon impact. Our landscape team is evaluating embodied carbon as a performance metric alongside other site sustainability goals. This includes developing ways to measure the embodied carbon and carbon sequestration potential of site materials, as well as the carbon impacts of site work and site maintenance requirements, planting details and material sourcing. This innovative design-thinking inspired a specific site element at the University of Oregon: the “stumpery” nurse log garden. Prompted by a discussion of the feasibility of upcycling existing landscape items slated for removal, the team harvested fallen trees from campus, selectively removed trees from the site for reuse as nurse logs and created specifications and nurse log details for construction.
As with so many elements of sustainable design, our knowledge and understanding of the problems to solve is continuously evolving. Success in one area exposes the next layer of construction practices that need to be addressed. We believe that an integrated design process—combined with R+D, and transparent sharing of knowledge and practices—will catalyze design solutions to the most important issues of our time.
Our membership in CLF has been a great opportunity for that sharing, building a community of practitioners to lead the way.