Using naturally resistant woods for outdoor applications makes a lot of sense. It allows us to avoid, for example, environmental risks from CCA-treated wood. Even with highly resistant wood, however, we can often take measures to increase durability. For fences and decking, for example, the USDA's FPL recommends treating the lumber with a clear, low-toxicity preservative, such as copper naphthenate or IPBC, then coating the wood with an exterior-grade, water-based finish such as paint or opaque stain. This finish forms a film that sheds water but allows water vapor to escape.

Alternatively, you can avoid wood altogether, choosing instead one of the new recycled-plastic or wood-plastic composite products on the market.

Alex Wilson is editor and publisher of Environmental Building News, a monthly newsletter about environmentally responsible design and construction. He lives in Brattleboro, Vermont.