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Building Products July 2017

ROOFING, CLADDING AND ACCESSORIES watching the weathering journey that such a natural material presents during its service life, others are keen to create a more uniform colour that gives some level of consistency over time. The trend for products offering colour durability is gathering pace and manufacturers are rightly focusing on adding solutions to their product range. Whilst Western Red Cedar continues to command the greatest share of the timber cladding market, coupled with other popular choices such as larch and pine, we are seeing high growth of niche brands in the modified wood sector, designed specifically to satisfy the demands for low maintenance and maximum durability. Accoya is such an example. Introduced just over ten years ago there is now some compelling performance evidence from cladding trials and early installations, reinforcing the credentials associated with the Accoya brand. Claiming a 50 year service life, sustainability and minimal requirements with regard to maintenance, this modified timber cladding product appears to be ticking many boxes for those prepared to invest in its long-term performance. More recently and quite innovatively, Accoya has been combined with Shou Sugi Ban, an ancient Chinese method used to darken the surface of the wood. The use of these two techniques in tandem is ideal as Shou Sugi Ban is applied over an already durable substrate. 28 BUILDING PRODUCTS | JULY 2017 The TDCA exists to provide the construction industry with comprehensive information and guidance regarding timber cladding, coupled with a source of high quality manufacturers and suppliers, many of which have achieved the industry recognised CladMark quality assurance scheme that is assessed and audited by third-party experts. Seeking to educate the industry and elevate the standards for the manufacture and installation of timber cladding, here are just three examples of the most common questions asked, with a brief explanation. Does larch cladding have to be preservative treated? As a general preservation industry rule, timber cladding should be manufactured to achieve a 30 year service life. To take Siberian Larch as an example, it is assigned to durability class 3: moderately durable which, if uncoated, equates to a desired service life of 15 years. Therefore, to achieve the desired 30 year life, preservative treatment is necessary. What type of membrane should be used for open jointed cladding? An open jointed arrangement will allow UV light to pass through to the breather membrane behind and so the first thing is to limit the spacing between the cladding joints to no more than 15mm. Furthermore, the membrane should be a good quality, UV stable product and matt black will certainly be less conspicuous. Insect mesh may also be necessary across the entire face of the wall and this will also reduce moisture penetration and ventilation into the cavity. Why can black streaks appear on cladding? Cladding should always be installed using corrosion resistant fixings suitable for outdoor use such as stainless steel, to prevent any potential for iron staining. The black staining seen here is most likely due to a chemical reaction between acidic natural tannins or extractives in the wood and iron present in steel products such as nails, screws and other fasteners. Product quality control and education regarding installation best practice are both paramount to ensure the long-term effective use of timber cladding. We saw the arrival of a brand new British Standard specifically for timber cladding in 2014: BS8605 Part 1. Covering all aspects under the manufacturer’s control, up to the point where the cladding leaves the factory, we are now looking forward to Part 2 of this Standard, due to be published in 2018. This will cover the installation of timber cladding and prove to be an excellent guidance document to help specifiers and installers provide an optimum result and further develop the positive reputation of timber cladding as a sustainable and highly adaptable building material. Janet Sycamore is Director of Operations at the Timber Decking and Cladding Association <<< Continued from page 27


Building Products July 2017
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