Little known fact: Chicago Principal Bill Bast, when he’s not making sustainable design decisions, is out saving the world.
Sustainable design has commonly been the realm of architects, but structural engineers make design decisions every day that influence the impact of buildings on the environment. At Thornton Tomasetti, we asked, “how can we as engineers help to create a more sustainable world,” when we became members of the AIA 2030 Commitment in 2010.
At that time, we were the first primarily structural engineering firm to join the Commitment, and the reporting requirement for calculating your projects’ operational energy didn’t seem to be an accurate measure of our work. Structural engineers can have a large impact on decisions about structural materials, and therefore we decided to instead report on the carbon embodied in the lifecycle of the materials used in our projects. Thornton Tomasetti recently submitted its fifth year of reporting on embodied carbon to the AIA.
According to Architecture 2030, presently the embodied energy of building materials represents anywhere from 15 to 20 percent of the total energy used by a traditional building over a 50-year period. Moreover, the reduced operational energy demands of new and retrofitted high performing buildings mean carbon dioxide emissions coming from the production of its materials and products represent a larger fraction of the total lifetime energy used.
One way structural engineers can help to reduce embodied carbon is to use less cement. According to the American Society of Civil Engineer’s Sustainability Guidelines for the Structural Engineer (ASCE-SEI), on average, for every ton of cement produced a total of 0.9 tons of carbon dioxide are emitted. This combined with its widespread use makes concrete one of the largest sources of greenhouse gas emissions in the construction industry.
Structural design can have some impact on the operational energy of a building as well. A significant amount of energy transfer typically occurs through a poorly detailed building envelope as a result of thermal bridging, the flow of heat through building materials via conduction – and structural engineers have the opportunity to make a big impact. For example, in a prototype, 3-story, 9,000 SF steel-framed structure analyzed by SEI/AISC, as much as 4% annual energy savings could be theoretically realized by accounting for thermal bridging in the structural design. While that may not seem like much, as building envelopes are designed to meet higher energy performance levels and mechanical systems become more efficient, the impact of thermal bridging will be an increasingly important consideration.
There are a number of other ways structural engineers can be sustainable designers, including designing for deconstruction and longevity, or maximizing daylighting with appropriate framing layout. A good resource for structural engineers who would like to do their part in saving the earth is the book “Sustainability Guidelines for the Structural Engineer,” co-authored by Kestner, Goupil, and Lorenz (2010) and published by the American Society of Civil Engineers (ASCE).
Thornton Tomasetti wishes you a Happy Earth Day!
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