When it comes to performance and the good looks of your timber cladding, the handling, storage and installation are just as important as the specification
Handling and Storage
Care should be taken when handling and storing cladding boards on site prior to being fixed. The boards must be protected from moisture, sunlight, dirt, scratching and mechanical damage, and should not be left in contact with the ground. Boards should be stacked on timber bearers with the top of the pack covered to protect against rainfall, left open at the sides allowing air to circulate freely and with the external surface of the boards face down. Cladding should ideally be fixed within two weeks of delivery, so establishing your supplier’s lead-in time and programming this accordingly into your build is a very good idea.
Your structural warranty provider or architect/surveyor engaged to provide a certificate acceptable to your mortgage company will insist on a ventilation gap behind the timber cladding which should be a minimum of 19mm (but I would recommend 25mm). Low and high level ventilation is required, behind the allowing cladding, the enabling free flow it to of dry air out after having been exposed to rain or snow; this will also improve the lifespan of the cladding. Particular care has to be taken above and below window and door openings to ensure adequate low and high level ventilation is provided at these points. Anti-insect/ vermin mesh should be fitted at both the low and high ventilation points.
Detailing at Openings
As with all forms of cladding, the devil is in the detail at perforations or changes of direction in the cladding and it is imperative that you/your architect/ cladding supplier agree the details for these areas so that the correct materials are supplied accordingly. Do ensure that the tradespeople employed to fit the cladding are given a copy of the details and advised that they have to be strictly followed.
How the timber cladding is fixed is fundamental to its long-term performance both in terms of appearance and durability. In my experience, a large percentage of detrimental issues with cladding are due to the timbers being incorrectly fixed. I would recommend using the best available grade of stainless steel nails/ screws in order to eliminate corrosive leaching, which is very unsightly and can completely spoil the look of the cladding. It is important that the nail/ screw is not overdriven into the board, as this will produce a ‘ bullet-hole’ effect which may compromise the durability of the board; ideally the head of the nail/screw should finish flush to the timber preventing water ingress at the point of fixing. Screw fixing generally gives a better end result as more care is taken in positioning and finishing the screw head flush with the timber surface. In order to prevent splitting at the board ends, pre-drilling is recommended for certain species of timber, or alternatively you could use one of the proprietary screws on the market that boast no pre-drilling being necessary due to their unique design, thus saving time on site.
Horizontal and Vertical Cladding
For horizontal cladding for timber frame and masonry builds, vertical regularised treated timber battens, a minimum 25 x 50mm (forming a 25mm ventilation cavity), should be fixed at a maximum of 600mm centres to which the timber cladding is then fixed. Boards should always be joined on a vertical batten, with the joints being staggered. The bottom edge of the bottom board should be chamfered to allow water to run off freely. The same goes for vertical cladding, except that horizontal battens, a minimum 25 x 50mm at a maximum of 600mm centres, are then fixed to the vertical battens and in turn the timber cladding is fixed. Vertical cladding should always be fixed with the growth rings pointing downwards and the bottom edge of the boards should again be chamfered to allow water to run off freely. Cladding should ideally be kept 300mm above the finished ground level and never less than 150mm, to avoid ‘splash staining’ caused by heavy rainfall on bare soil and moisture absorption by the cladding when there is excessive snowfall.
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