Comparing the most common decking material, solid lumber, with WPC decking – a material without a long-term track record of use – requires a bit of a leap of faith.
The qualities of WPC decking, on the other hand, are largely defined at this point by manufacturer’s claims and those of various NGOs and other organizations. The EPA is quoted by Fox News as reporting that WPC products last indefinitely (Cant 2009). The EPA’s GreenScapes website , in fact, appears to wholeheartedly endorse plastic lumber over traditional materials for a wide variety of applications. But is sweeping endorsement justified? Is everything that is being said, in fact, true? A bit of investigation into WPC performance to date suggests that caution may be in order when considering such products. For instance, various sources document a number of problems that have been encountered with plastic composite decks and a recent study offers new information to help evaluate environmental impacts.
Before examining problems that have been encountered with WPC products it is worth noting that such products are relatively new, and that ongoing R&D is focused on addressing current problems. Morrell et al. (2010) and Breslin (2010) describe additives and processing modifications that have already helped to reduce performance problems. Shut (2005) also discusses efforts to improve product performance. Continued effort can be expected to improve the performance of these products going forward.
While there have been detractors (Platt et al. 2005), plastic lumber is often promoted as a green product based on the fact that it is typically manufactured from recycled plastic and also because of perceived longevity and relative freedom from maintenance. Up until recently, however, there has been no systematic analysis of the environmental impacts of WPC lumber production and use. A new report from FPInnovations (Mahalle and O’Connor 2009) details the results of a life cycle assessment of western red cedar vs. WPC decking. The study was commissioned by the Western Red Cedar Association, but performed independently by FPInnovations-Forintek Division. It is the only known LCA conducted to date on solid wood vs. WPC decking.
Comprehensive life cycle comparisons of treated solid wood and WPC lumber products have not yet been conducted. However, an indication of how treated solid wood lumber might compare to WPC lumber with regard to environmental measures can be obtained by studying life cycle comparisons of treated and untreated lumber, and then considering findings in light of the comparison of naturally durable lumber and WPC lumber discussed previously.
For instance, a life cycle comparison of treated and untreated lumber is included in the Building for Environmental and Economic Sustainability (BEES) program of the Building and Fire Research Laboratory of the National Institute for Standards and Technology (National Institute for Standards and Technology 2007). This analysis shows higher impacts for treated wood than those associated with untreated wood in every environmental performance category. However, the weighted environmental performance score across all categories shows impacts only marginally higher than for untreated wood (Figure 5). As a result, a comparison of solid treated wood with WPC composite lumber can be expected to show similar results to the comparison of naturally durable, untreated solid wood to WPC lumber. An important difference relates to the presence of added chemicals in treated wood that are not present in either untreated wood or most WPC lumber products.