Adam Taylor, University of Tennessee and Richard Bergman, US Forest Service.
The environmental advantages of wood products are important and may be common sense to many; however, not everyone recognizes and understands these merits. Life cycle assessment (LCA) is method for evaluating the environmental impacts of products. LCA is a holistic, scientific approach that considers the resources consumed and the emissions released during a product’s manufacture, use and disposal. LCA studies consistently show that wood products are better than alternative materials in terms of their environmental impacts.
Life cycle assessment procedures are standardized and described in the ISO14040 series (Figure 1.) Briefly, LCA begins with definition of what is to be studied and why. The product of interest, its function, the parts of the life cycle to be studied and the purpose of the study are all explicitly described. Then, a life cycle inventory (LCI) is generated, which is a detailed account of all the inputs and emissions associated with the product of interest. A life cycle impact assessment (LCIA) is used to help simplify and interpret the detailed and lengthy LCI. Models are used to organize the components of the LCI into groups with similar effects (e.g. both carbon dioxide and methane emissions contribute to climate change). These models report potential impacts in commonly-used categories of interest such as Global Warming Potential (GWP) and Acidification Potential. Accessing the meaning and significance of the LCI data and the LCIA results is a complex and iterative process depending on the goal of the study. LCA does not provide a single number or qualitative evaluation.
Figure 1. The generalized process of life-cycle assessment (LCA). Source: http://en.wikipedia.org/wiki/File:PhasesOfLifeCycleAnalysis.png
Life cycle assessment can identify manufacturing stages with higher environmental impact (“hot spots”). For wood products, the impacts of the manufacturing stage (especially drying) that focus primarily on energy and material usage usually are substantially higher than those associated with forestry practices such growing and harvesting trees. However, other environmental impacts related to forest resource activities such as biodiversity and land-use changes have become more of a concern and can be difficult to quantify with standard LCA framework although LCA has made progress in this endeavor. Regardless, sustainable forest management schemes like Sustainable Forestry Initiative or Forest Stewardship Council ought to be incorporated to aid forest landowners in dealing with these complex issues. Life cycle assessment also can be used to compare the environmental impacts of products; consumers can use this information to choose products with better environmental profiles. Many cradle-to-gate LCA studies have been made of wood products (see www.CORRIM.org) and their non-wood alternatives. These studies consistently show a low emission environmental profile for wood, compared with non-wood products that can serve the same function.
Performing an LCA for a product is a detailed, data-intensive process and the results may be difficult to interpret for non-experts. Thus there is a need for simplified metrics from LCA studies of wood products, especially to enable consumers of building products to choose materials with favorable environmental footprints. Environmental product declaration (EPD) is the term that is used to describe a summary of the environmental impacts associated with a product and as with LCAs, EPDs’, follow an internationally-accepted standard in their development, ISO 14025. An EPD is based on a life cycle assessment (LCA) and can be used to compare products on an equal basis if the units for the different product serve the same function for the same time. EPDs for structural building products such as wood and steel studs are good examples that could fall under this approach. EPDs are meant to communicate standardized LCA information in a way that is meaningful to people who may not be familiar with LCA. An EPD is analogous to a ‘food label’ for products (see Figure 2).
Figure 2. Life cycle impact assessment data for a wood ‘2×4’. Such information would be listed in an EPD.
EPDs are a recent development and are being promoted as a way to improve the quality, credibility, and transparency of environmental impact information available to consumers and businesses. This trend is already affecting wood producers in the United States that exports to countries in Europe that are starting to require EPDs or a sub-set of EPDs for products sold in their countries.
Because EPDs are based on LCA, they have some of the same weaknesses of that methodology. These include the static (snapshot in time) nature of the evaluation, the burden of data collection and analysis and the potentially large importance of underlying assumptions such as product geographical source and the allocation of environmental burdens to co-products. However, the LCA and EPD development processes are transparent, so these potential weaknesses should be readily apparent, and the significant data demands reflect the effort to base the evaluation on objective measurements.
EPDs could provide a way to communicate the environmental benefits of wood to consumers. EPDs could relatively easily be incorporated into purchasing preference programs and green building rating systems. For example, if EPDs for cedar and vinyl siding were available, the smaller global warming potential of the wood siding product would be readily apparent to a potential customer, construction specifier or building impact evaluator. The ATHENA Institute, a North America-based non-profit, currently uses life cycle information from CORRIM and other sources in its databases and analysis tools that help architects, engineers, and other to evaluate the environmental impacts of whole buildings made from different materials.
The need for credible and transparent environmental product information is likely to increase. LCA-based EPDs can provide this information and help consumers to understand that “wood is good.”