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A Life Cycle Assessment (LCA) is a methodology to determine the environmental impact of a product, process, or service. It is analogous to environmental accounting. A LCA would be useful in answering a question such as, “Is it better to use concrete or steel for a new office building?"
The four stages of a LCA are goal and scope definition, inventory analysis, impact assessment, and interpretation (see Figure 1). These steps help define what is included in the study, the environmental ‘costs’ (e.g. CO2 emissions) of each item, how these impacts relate to larger scale environmental concerns (e.g. global climate change), and final how do we use this information (e.g. climate mitigation strategies for green building).
The International Standards Organization (ISO) 14040 and 14044 set forth the framework for performing a LCA. They define options in methodology and scope, uncertainty analysis, and peer review requirements. Delving into these standards is not mandatory to performing an LCA-based calculation though. Even a simplified LCA that uses material quantities and life-cycle inventory information alone will benefit building designers who are looking to make decisions that better sustain our environment.
Environmental sustainability has been widely accepted as a criterion for development in the twenty-first century and beyond. At the same time, several environmental systems (e.g. the atmosphere’s ability to absorb greenhouse gas) are reaching, or have reached, their capacity. Thus, the desire to have a green society is no longer sufficient; improved environmental perform is necessary. LCA offers the tools to move beyond simplistic assumptions and determine true environmental impacts.
LCA takes into account impacts over a full life-cycle, not just a snapshot that vendors will often focus on to claim sustainability credentials. For structural materials, the life cycle generally includes extraction, manufacture, transport, construction, maintenance, and end-of-life. Thus LCA provides the most complete picture of environmental effects inherent to choosing certain structural materials.
Furthermore, an LCA allows one to evaluate performance across a variety of impacts. It is common to see manufacturers touting environmental merits based on a single characteristic, like recycled content, but when it comes to materials, there are often trade-offs of between impact categories. LCA recognizes this, 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.
The best way to learn more about LCA is to do a LCA yourself! Often simply doing the Life Cycle Inventory (LCI) is sufficient to understand the resultant magnitudes under consideration.
A good place for US data is at the National Renewable Energy Laboratory – U.S. Life-Cycle Inventory Database (http://www.nrel.gov/lci/).
For assessing embodied impacts of building structures in the US, there are two prominent software packages, both of which have freely downloadable versions.
More sophisticated software, geared for products, is available through larger companies who provide more detailed information on performing a LCA that meets the ISO 14040 and14044 standards.
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