Natural Wood Durability Studied to Estimate Wood's Performance
Naturally durable wood (NDW) has been offered as an alternative to chemically treated wood for the environmentally conscious consumer. Extractives contained in certain wood species are thought to impart natural durability, but extractive content varies drastically based on a variety of factors making performance estimates of NDW difficult. The goal of this research is to provide analyses of the role of extractives, how they improve the durability of certain wood species, and provide reasonable field-based estimates of performance of these materials.
The use of naturally durable wood predates treated wood by thousands of years. Many structures thoughtfully constructed of these NDW materials have endured for centuries. The removal of chromated copper arsenate, or CCA, a common chemical wood treatment, from the residential market in 2006 drew attention to the limitations of treated wood in environmentally sensitive areas. As a consequence, several NDW types, such as redwood and western red cedar, were marketed to consumers as alternatives to treated wood.
Understanding of the actual mechanisms of the natural durability of wood is limited; however, extractives are believed to be key factors. Forest Service scientists are working to gain a better understanding of the role of extractives as NDW weathers in the natural environment, and the effect of extractives on the microbes that drive wood deterioration.
Nine candidate NDW species are being evaluated in aboveground and laboratory tests to develop recommendations for consumers interested in using NDW in nonstructural applications. DNA (deoxyribonucleic acid) extracted from fungi and bacteria that are colonizing the woods is being analyzed to see if different microorganisms attack different wood species. Chemical analyses are being conducted to determine the different chemical components found in NDW and how those components change during outdoor exposure.