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Building Products April 2017

TIMBER AND TREATMENTS MOISTURE CONTROLS Timber has long been a popular choice for cladding thanks to its sustainability and natural appearance, but some may still harbour concerns about moisture causing swelling, warping or even rot. Phil Barman looks at the developing trend for thermally modified timber cladding and how it can overcome these potential issues while retaining its environmental benefits. Timber’s sustainability and natural APRIL 2017 | BUILDING PRODUCTS 49 appearance makes it a popular choice for cladding, with local authorities, architects and developers specifying timber for both aesthetic and practical reasons. Not only is timber a visually attractive choice with countless varieties and finishes to choose from, most hardwoods and even some softwoods have a life-expectancy of decades. There are undeniable environmental benefits of working with a natural, sustainably-sourced material with the credits to be gained under the BREEAM energy rating and the Code for Sustainable Homes accounting for its popularity in both commercial and residential schemes. Unlike pvc, timber cladding is 100% recyclable, so it can be invaluable to building projects that include firm targets relating to carbon neutrality. It is also very easy to work with, being lightweight and easy to trim and fit. Projects that require temporary cladding can turn to timber for a solution that can be demounted and reused. What’s more, cladding acts as an insulator, reducing the building’s energy costs and muffling outside noise. However, working with a natural material also has its potential drawbacks, and there are issues that architects and project managers should be aware of before specifying timber cladding. The main issue is that untreated timber has a tendency to warp or swell or shrink due to changes in moisture: for example, green oak can shrink by up to 7%. Timber with a moisture content of 20% or more allows acetic acid to be produced which will corrode mild steel and galvanised steel fixings, and can cause staining on the cladding. Timber cladding could also suffer to fungal decay or damage caused by insect attacks. Harsh chemical treatments can have harmful environmental effects which counteract some of the sustainability points won by specifying timber rather than a non-renewable material. The same is true of importing exotic hardwoods: the energy required to transport the timber from beyond Europe reduces its green credentials considerably. Thermally modified timber provides a viable solution to many of the potential drawbacks of untreated wood, increasing the durability of the material without the use of chemicals. There has been increased interest in these products over the past few years, leading to suppliers developing full thermally modified timber cladding ranges in response to this demand with a choice of styles and finishes. It may come as a surprise that a version of this method existed – albeit in a very primitive form – over 1,000 years ago, with evidence that the Vikings burned the exterior of wooden fence posts Continued on page 50 >>>


Building Products April 2017
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