Comparing EPDs
Given numerous thermal insulation EPDs have now been published, is it possible to make meaningful comparisons among the data they report? The answer must be qualified. As stated, EPDs for similar products must use the same PCR so the scope, methodology, data quality, and specific environmental indicators are equivalent. However, several other important caveats should be noted.
LCA and the development of EPDs is a very young practice, especially in North America. Although there are well-established ISO standards, considerable variations within the actual application of those standards can be found. Additionally, the underlying LCA databases are evolving constantly as new data becomes available. It is possible the newest LCA data may contain different levels of impact—simply due to improvements in measurement precision.
The way similar materials are installed within a building may also affect the validity of comparisons. As an example, insulation may be installed either continuously over the wall framing or roof deck, or it may be installed within wall or roof cavities. When it is installed continuously, the R-value provided is uniform. However, when installed within a cavity wall, the overall R-value is reduced by the lower R-value of the framing materials, such as 2x4s or concrete masonry units (CMUs). This means the functional R-value per square meter of wall or roof area will be lower than the functional unit of the insulation EPD and, as a result, an effective comparison between an insulation product installed continuously and one installed within a cavity is impossible.
Perhaps most importantly, minor differences among small building components may not yield significant impact savings when applied to an entire building. The concept of size versus the effect of any particular impact is very important. In many cases, the measured impact may be so minute that even when you scale up from the functional unit to an entire building, the overall impact remains relatively minor.
| ADDITIONAL RESOURCES |
| For a look at how the data disclosed through environmental product declarations (EPDs) will be used in lifecycle databases, whole-building lifecycle assessments (LCAs), product manufacturing improvements, and green guidelines and codes, visit www.constructionspecifier.com/more-on-epds to read a feature by this article’s author.
For the reader looking for additional information about EPDs, the following resources may be very helpful:
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The use of scientific notation for very small measures of impacts in EPDs may help to illustrate the issue of impact size and effect. To expand understanding of size and effect, let’s go back to the example of the impact of eutrophication in the generic polyiso roof EPD previously discussed. In the EPD impact table for polyiso roof insulation shown in Figure 6 (page 32), the eutrophication impact of one square meter of polyiso roof insulation at the prescribed functional unit is 1.40E-03 or 1.40 thousandths of a kilogram of nitrogen. If this measure is then extrapolated to a 929-m2 (10,000-sf) building with R-20 roof insulation, the net eutrophication potential for the roof insulation would amount to slightly more than 4 kg (8.8 lb) of nitrogen.
Converting this amount of nitrogen into a more tangible example, those 4 kg of nitrogen would be equal to the amount of nitrogen in fertilizer needed to produce approximately four bushels of corn. So, if you were able to find a roof insulation with only half the eutrophication potential as in this example, the net environmental savings over the entire lifetime of the building would be equal to the net impact of two bushels of corn. This is not to say every bushel of corn is not important, but there are probably many other energy and environmental impacts to consider before making a definitive judgment regarding the use of a particular insulation material based on eutrophication potential alone.
For the construction specifier, it may be important to remember whenever comparisons are available, someone typically will use them to differentiate products in the marketplace. In some cases, comparisons may come from product manufacturers, but it is also likely green building advocates will employ comparisons to promote the use of ‘green materials.’ Consequently, it will be important for every building envelope consultant to fully understand the EPD process so comparisons may be accurately analyzed and interpreted for clients.
Conclusion
Based on this brief overview of EPDs, several conclusions may be suggested. First, it is likely the environmental product declaration will become an important tool in sustainable material selection and building design. Additionally, EPDs are obviously destined to play an important role in future building standards and codes. Finally, this review provides considerable support for the proposition that EPDs are being developed under rigorous standards to help assure scientific accuracy and functional comparability. However, there are a number of limitations in comparing EPDs at this time, partly due to the relative infancy of the EPD itself as well as issues involving the significance
of differences observed. As a result, the better informed a construction specifier is in regard to EPD processes, the better value the consultant can provide to the end-user.
Given the number of EPDs that will become available within the next year or two, specifiers will likely be able to learn much more about the tool’s usefulness in the near future. In fact, as a building researcher, this author admits he is personally interested in digging deeper into EPD data and providing additional analysis for the consulting community. Based on an initial look at many of these EPDs, there will be real value—and a few surprises—as the industry continues to move to a more quantifiable approach to sustainable material selection.
James L. Hoff, DBA, is an experienced executive and researcher in the building materials industry, retiring as vice president of technology for Firestone Building Products in 2007 after 23 years of service. Hoff currently serves as president of TEGNOS Research, a consulting organization dedicated to expanding understanding of the building envelope. He holds undergraduate degrees in psychology and architectural design, as well as a master’s and doctorate in management. Hoff has published numerous articles on building system performance, quality management, and lifecycle analysis (LCA). He can be reached at jhoff@tegnos.org.
