Feature Article

Treated Wood in Transition: Less Toxic Options in Preserved and Protected Wood

During a major renovation of the Frederick, Maryland, town library, the main entrance was moved from the town’s main street to a courtyard near the back of the library. The architect designed a covered walkway completely detached from the original building; it was simpler and faster to build, honored the continuity of the existing wall’s water management, and was less expensive than any attached walkway would have been.

Photo: Peter Yost
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 (see

EBN

Vol. 11, No. 3). 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 (140 million m

3) 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 (92 million m3) of softwood lumber per year, of which roughly 8.4 billion board feet (20 million m3) are being treated for outdoor decks, sill plates, interior framing in termite-prone locations, 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. While particularly relevant to residential building, where decks are the main use of treated lumber, this article applies to any building type in which treated wood is used.

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% of all treated wood volume in North America, including some non-residential building applications.

Published July 31, 2006 Permalink