Life Cycle Assessment of Building Products

New tools increase environmental transparency for verifiable sustainability
This course is no longer active
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Sponsored by CalStar Products, Inc.
Peter J. Arsenault, FAIA, NCARB, LEED AP

Cradle-to-Job

This version of an LCA accounts for everything in the cradle-to-gate assessment and adds in the transportation to the jobsite. Obviously there is some variation here given the distance of the manufacturing location to any given jobsite, so some assumptions need be made. There will also be differences in the weight or size of different products that will impact the transportation impacts. Nonetheless, typical shipping conditions can be identified in PCRs that allow reasonable comparisons, and the maximum distances can be determined based on the number of plants and their geographic locations. For example, products that are available from multiple plants around the USA are likely to have less jobsite transportation impact than those made only in one overseas location.

Cradle-to-Grave

This is a full LCA that addresses all life cycle phases beginning with cradle-to-job described above plus construction/ installation, use in the building over time, and the end-of-life phases. Some generalizations and average conditions obviously need to be assumed for the later phases since they are speculative about the future, but it is again the role of a PCR to help identify and narrow down those choices so fair comparisons can be made.

The boundary sets described above are an important element in life cycle assessment and associated EPDs. The PCR specifies what boundaries should be used in the LCA for measurement (such as cradle-to-gate or cradle-to-grave). Simply put, it defines where the assessment starts and stops. Does the LCA consider the electricity used to power the plant and also the energy required to create that electricity? Does the EPD include cradle-to-grave impacts (all life cycle phases) or only cradle-to-gate impacts (raw material extraction and manufacturing phases) but not construction, use, or end-of-life phases? Any of these may be valid, but it is important to know what set of boundaries is being used when looking at different EPDs. From an architect's perspective, the most versatile EPDs present impacts by each of the life cycle phases, which allow us to compare environmental impacts with appropriate boundaries in mind. This is important if one manufacturer has published a cradle-to-gate EPD and another has published a cradle-to-grave EPD. In this situation, for a meaningful comparison the user should look at cradle-to-gate impacts, as that is the information available for both products.

Comparing Green Building Products

Design decisions are often made early regarding the basic materials and products that become part of the building. The best way to ensure that a green construction system is being used and to compare green building products objectively is to request EPDs right up front during the early design process. This is particularly true when considering basic products or materials such as comparing a concrete building to a masonry building or whether to use steel, aluminum, or other metals. Later in the design and documentation process, it is also appropriate to request EPDs from different manufacturers for the same product type to identify any specific differences between one compared to another. It is also now quite appropriate to specify products based on specific declared environmental criteria such as limits on carbon footprint or embodied energy. And of course, making EPDs a required submittal in the project specifications is the best way to verify that the materials used in construction match those specified.

Regardless of the points in time that the comparisons are done, the ideal method is to review multiple EPDs at once and compare them side by side. For a true “apples to apples” comparison, it is important that each of EPD is based on the same PCR since that will set the guidelines and assumptions of the LCA as well as define the functional unit of the material. It is also critical that the EPDs each address the same LCA boundaries so that products can truly be compared on an “apples to apples” basis and selected based on having the lowest actual environmental impacts.

Obviously the use of EPDs makes the green comparison of products rather straightforward and informs decision-making throughout the design and construction process. However, what do we do when we need to compare products where EPDs are not available? In that case, we need to look at the analysis of materials provided by generic LCAs. The best known and commonly available way to do that is to use the BEES Online (Building for Environmental and Economic Sustainability) database developed by the National Institute of Standards and Technology (NIST) Engineering Laboratory. This is a very useful tool that can be used for generic LCAs based on consensus standards and is designed to be practical, flexible, and transparent. BEES Online, aimed at designers, builders, and product manufacturers, includes actual environmental and economic performance data for 230 building products. BEES measures the environmental performance of building products by using the life cycle assessment approach specified in the ISO 14040 series of standards. All stages in the life of a product are analyzed: raw material acquisition, manufacture, transportation, installation, use, and recycling and waste management. Economic performance is also measured using the ASTM standard life-cycle cost method, which covers the costs of initial investment, replacement, operation, maintenance and repair, and disposal. Environmental and economic performances are combined into an overall performance measure using the ASTM standard for Multi-Attribute Decision Analysis. For the entire BEES analysis, building products are defined and classified according to the ASTM standard classification for building elements known as UNIFORMAT II.

 

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Originally published in April 2013

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