In some instances timber doesn’t need preservation treatment at all. Take the two medieval barns at Cressing Temple in Essex, just featured in a Sunday Times travel supplement. One of these giant oak-framed buildings dates back to the beginning of the 13th century. The second is a mere strippling, built in 1250. Taking into account the age of the trees when they were felled, the wood could be pushing 900-years old, and it’s still tough as old boots.
That said, though, in many applications where timber is exposed to the elements and particularly when it’s in ground contact, it does need some form of treatment to back up it’s natural durability. And for the last 70 years, or so, that has commonly meant a dose of copper chrome arsenic solution (CCA). Inevitably with arsenic in the mix, this treatment has received quite a lot of bad press and close scrutiny from governments and health organisations worldwide. Despite the fact that, according to bodies like the British Wood Preserving and Damp-proofing Association, the treated timber has caused no recorded health or environmental problems, it’s now official that the EU will prohibit it from specified residential applications next year . The treatment industry has seen this coming and developed highly effective alternatives to CCA. But a risk which has been highlighted is that the latest EU ruling, and similar legislation in the US, could persuade the timber sector to drop CCA completely, even for the “higher hazard and critical end use” industrial and commercial applications where CCA Type C is still allowed. In turn that could result in a headlong rush to alternatives in areas where, unlike CCA, they have not yet been tried and tested by the treatment sector. If problems result, it could tarnish the industry as a whole.
The solution, says the BWPDA, is an “orderly transition” to newer preservatives, with the industry continuing to use CCA where it’s permitted. That way, timber’s centuries old reputation for durability will last even longer.
