Which is the more sustainable structural material, steel or concrete? Can wood products actually negate carbon dioxide emissions? Is it better to renovate an older, less-efficient building or tear it down to build a high-performance new building? What are the most effective sustainable design strategies that a structural engineer can pursue?
Until recently, a structural engineer could find only anecdotes as answers to these questions. Today, life cycle assessment can provide detailed metrics on the environmental impacts of many products and processes. The assessment of environmental data starts with demands on natural resources, energy consumption, and creation of waste. And from there one can forecast the effects on human respiratory health, ozone depletion, water quality, smog formation, and global warming.
To answer these and other common questions about sustainability, the Structural Engineering Institute’s Sustainability Committee researched recent life cycle assessment case studies. Our goal was to provide reputable research with quantifiable data on the sustainable alternatives. We discuss these questions in 10 blog topics at http://tiny.cc/SEItop10LCA.
Life cycle assessment research shows that the proportion of energy needed to manufacture a building’s materials, much of which is structure, accounts for 5 to 30 percent of its total life cycle energy. The rest of the energy is used to operate the building: heating, cooling, and powering. One of the best things a structural engineer can do is integrate the structural system into the optimization of the building operations. As energy codes continue to restrict operational loads toward “net zero,” structural engineers will need to do more by reducing the embodied energy footprint of the structure.
Saving building materials is one tried and true method. Renovating older buildings usually saves energy, materials, and emissions compared with a standard new building. It may take 50 years for a new building with 30 percent better energy efficiency to outperform a renovated building.
Regarding steel and concrete, there is no clear winner. Our blog delves into the strategies to optimize both. Wood structure gets more complicated. When one measures the carbon dioxide emitted during its harvest and manufacture, wood products can be “carbon negative” because trees absorb carbon dioxide as they grow. But at the end of a wood product’s life, the sequestered carbon dioxide will be released through decay. This is one of the many reasons one should compare materials throughout the entire life cycle, preferably within the same data set or study.
So what are the best sustainability practices for structural engineers? Visit our blog for strategies with measured benefits backed by life cycle assessment research.
Adam Slivers, S.E., is a consulting engineer at Lund Opsahl LLC and a member of the SEI Sustainability Committee. The committee’s website is www.seisustainabiltiy.org. Slivers can be reached at firstname.lastname@example.org