As building codes and green building rating systems evolve, lifecycle assessment (LCA) is gaining in popularity as a sustainable design metric. A few examples illustrate this trend:
- International Green Construction Code (IgCC) 2012 offers multiple project elective points if a whole building LCA is conducted;
- In the development of upcoming LEED v4 (previously titled LEED 2012), whole building LCA is a materials and resources credit option that has been maintained through four rounds of public comment;
- American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) 189.1 allows the use of LCA as a performance option for selecting a building's materials in lieu of prescriptive minimums for recycled, regional, and bio-based materials;
- Living Building Challenge 2.0 requires an embodied carbon calculation of the project within the materials petal;
- Greenroads and the Institute for Sustainable Infrastructure's (ISI) Envision, both infrastructure rating systems, contain prerequisites and/or credits for LCA-based evaluations; and
- International rating systems such as the UK's BREEAM, Germany's DGNB and Hong Kong's BEAM Plus all contain tools to evaluate building material impacts using LCA.
Why is LCA important?
LCA moves beyond simplistic assumptions to determine more accurate impacts to the environment and human health. LCA has two principal benefits:
- It can account for impacts over the full lifecycle of a building, not just a narrow snapshot that vendors may focus on to claim sustainability credentials. For structural materials, the lifecycle generally includes extraction, manufacture, transport, construction, maintenance, and end-of-life. Thus, LCA provides the most complete picture of environmental effects inherent in choosing certain structural materials, which is just one part of the larger building LCA.
- LCA also allows one to evaluate performance across a variety of environmental and human health impacts. It is common to see manufacturers touting environmental merits based on a single characteristic (e.g., recycled content), but there are often tradeoffs for materials between types of environmental impacts. LCA recognizes this and provides the most complete information through the inventory and allows the user to make choices weighted by goals and priorities on a case-by-case basis.
How can I perform my own LCA?
The best way to learn more about LCA is to do an LCA yourself. An LCA is useful in answering fundamental design questions, such as: How much energy is saved by adding supplementary cementitious material to a concrete mix? Often just the first step of an LCA, a lifecycle inventory analysis (LCIA) is sufficient to understand the magnitudes of design decisions under consideration. An LCIA tabulates the material and energy inputs and waste and emission outputs for a specific product or manufacturing process.
It is essential to remember that LCA is a methodology to determine the environmental impact of a product, process, or service. It is analogous to environmental accounting. Results are only as reliable as the data going into the accounting, and comparisons can only be made across studies following the same set of assumptions. This is why we often see a range in final impacts, and sometimes conflicting conclusions, particularly when comparing similar buildings constructed with different structural materials. LCA is more useful for indicating what can be done within a given system to reduce impacts (e.g., reducing cement or sourcing locally).
The International Standards Organization (ISO) 14040 and 14044 set the framework for performing an LCA. They define options in methodology and scope, uncertainty analysis, and peer review requirements. However, delving into these standards is not mandatory for performing an LCA-based calculation. Even a simplified LCA that uses material quantities and lifecycle inventory information alone will benefit building designers who are looking to make more sustainable-oriented decisions.
Assessment of the embodied impacts of building structures, materials and simple assemblies in the U.S. can be carried out using three well-known online software tools:
- Athena Impact Estimator (www.athenasmi.org)
- Athena EcoCalculator (www.athenasmi.org)
- BEES (www.nist.gov/el/economics/BEESSoftware.cfm)
If one has a material takeoff, it is straightforward to have Athena Impact Estimator report impacts for unit material quantities using the Additional Bill of Materials function.
More sophisticated software, geared for products, is available through larger companies that provide more detailed information on performing an LCA in accordance with ISO 14040 and 14044 standards:
It is essential to remember that LCA is a methodology to determine the environmental impact of a product, process, or service. It is analogous to environmental accounting.
A good source for inventory data in the U.S. is the National Renewable Energy Laboratory – U.S. Life-Cycle Inventory Database (www.nrel.gov/lci/).
Turning 'the inevitable' into an opportunity
The transition from simple assumptions regarding environmental design to LCA offers structural engineers several opportunities. It allows for recognition of a wider set of design and specification choices, which shifts more weight of decisions from the contractor and architect to the structural engineer. With LCA, higher-level design decisions (e.g., design for deconstruction, resilient structures, and utilization of thermal mass) can potentially be taken into account. While the tools and use of LCA in practice are continuing to improve, structural engineers can position themselves better by engaging in these changes. Structural engineers can utilize this as an opportunity to illustrate their contribution to sustainable design.
John E. Anderson P.E., LEED AP BD+C, is a Ph.D. candidate at the Technical University of Munich, at the Institute of Energy Efficient and Sustainable Design and Building. Frances Yang, S.E., LEED AP BD+C, practices structural engineering and sustainability consulting between the Buildings and the Energy & Resources groups at Arup, San Francisco. Adam Slivers, S.E., is an Associate at KPFF Consulting Engineers. All three are members of the SEI Sustainability Committee. The committee's website is www.seisustainabiltiy.org