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American Society of Landscape Architects


November 2006 Issue

Treated Wood in Transition
Alternative wood treatments can be less toxic for the environment and humans.

By Tristan Roberts

Treated Wood in Transition Wood Treatment Products Inc.

The treated-wood industry is in the midst of major changes today. The leading treated-wood product, chromated copper arsenate (CCA), was taken off the market for many uses at the beginning of 2004. The mainstream, copper-based replacements for CCA corrode fasteners more rapidly than CCA, increasing the risk of collapse for thousands of decks and other structures. Some of the new chemical treatment systems are entering the market with very little scrutiny from regulators, while one of the most promising treatment alternatives, TimberSIL, is the target of a campaign by the industry to get regulators to reclassify it as a toxic chemical—even though it isn’t toxic. And meanwhile, the 60 billion board feet of CCA-treated lumber that’s been put in service over the past 40 years is getting old; huge quantities are coming out of service and being disposed of, posing an environmental nightmare.

Wood is a natural resource, and there is much to be said for increasing its durability. In North America, we produce roughly 39 billion board feet of softwood lumber per year, of which roughly 8.4 billion board feet are being treated for outdoor decks and other uses. Treating softwood lumber with preservatives can make the difference between complete disintegration within months, in the worst conditions, and the same wood lasting decades, saving billions of board feet over time. The challenge is to gain this benefit in a way that doesn’t replace one environmental concern—cutting down trees—with others, such as heavy-metal pollution and toxic leachate from landfills.

There is much to consider among the various treated-wood alternatives. This article examines the world of protected and preserved wood: positive trends, growing concerns about disposal and toxins, and both promising and troubling materials entering the market. Two conventional wood preservatives, pentachlorophenol (“penta,” or PCP) and creosote, are outside the scope of this article, though it is worth noting that despite well-documented health risks and environmental problems with both, each still represents 10 percent of all treated-wood volume in North America, including some nonresidential building applications.

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