036 RCI 0517

RCI May 2017

CLADDING & SHEETING A thermally modified approach: timber cladding makes its mark 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. With that in mind, Howarth Timber’s Phil Barman explains why he feels the developing trend for thermally modified timber cladding is growing and how it can circumvent these potential issues while retaining its environmental benefits Timber’s sustainability and natural appearance makes it a popular choice for cladding, with local authorities, architects and developers specifying timber for aesthetic and practical reasons. Timber is built to last, with a life expectancy of decades, and there are undeniable environmental benefits of working with a natural, sustainablysourced material. It’s also very easy to work with, being lightweight and easy to trim and fit when compared to alternatives like PVC. Unlike PVC, timber cladding is 100% recyclable, so it can be invaluable to building projects that include firm targets relating to carbon neutrality. 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, untreated timber has a tendency to warp or swell when subjected to moisture and harsh chemical treatments can have harmful environmental effects. In my view thermally modified timber provides a solution to both problems, increasing the durability of the material without the use of chemicals. At Howarth Timber we have noticed 036 MAY 2017 RCIMAG.COM growing interest in these products over the past few years, leading to the development of a full thermally modified timber cladding range in response to this demand. 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 to protect them from the worst of the elements. However, it was in the 1990s when the technology started to develop in its current form. How to treat timber Today, the treatment involves heating timber to over 200°C, with steam used to prevent cracking and burning. Once cooled, the wood is remoisturised to around 5%. The principle is simple: heating timber removes most of the moisture, making it less likely to warp or swell, and as the treatment also removes resin, sugars which fungi would survive on are eradicated. Installers report that thermally modified timber is easier to cut with reduced wear on tools, and as the resin has been removed it’s lighter too, making installation easier. Unlike chemical methods, the treatment penetrates all the way through the wood so thermally modified wood won’t be subject to rot at the core. However, because the cell structure of the timber is permanently altered, installers must take extra care and follow fitting instructions carefully. Thermally modified timber is more brittle than untreated wood, so it’s best to use pre-drilled boards and hand nail boards into place to avoid splitting. Thermally modified timber should be installed using stainless steel fittings only. As a key component of cladding is weatherproofing, thermally modified timber’s increased weather resistance makes it a sound choice. This increased resistance to moisture means that the cladding is suitable for outdoor and indoor use, such as in a bathroom, wetroom or steam room. Thermally modified timber has aesthetic advantages as well, which can make it preferable even to exotic hardwood cladding. Many architects specify Western Red Cedar because of its famously rich colour, but in fact results can vary with some timber showing light pinkish tones rather than the desired reddish brown. Kiln-dried Western Red Cedar is rare, and air-drying results in variance in moisture in the timber so it weathers unevenly, resulting in what I’d describe as a patchy or even grubby-looking appearance. Both thermally treated Redwood and Clear Pine products offer the same rich colour as Western Red Cedar, but the treatment means that the timber will weather evenly, giving a better aesthetic effect with significant cost savings. As both timbers are sourced from Europe and are available with PEFC or FSC certification, there are clear sustainability benefits too. Mercia Marina Howarth Timber cladding section


RCI May 2017
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