Fixing Information

Nail fixings should be at least 55mm from the end of the boards. This may require wider or additional fixing battens behind. For all boards to be left without a surface coating austenitic stainless steel nails should be used in order to avoid long term rust stains on the wood. This is especially important on woods with high tannin content such as Oak, Western Red Cedar and Larch, where the reaction between the tannin and any ferrous metal will produce purple-black staining which is difficult to remove.

Stainless steel will weather to a matt grey colour similar to that of bleached wood. Using diffracted nail heads will help reduce the visibility of nails. Even if the cladding is to have a surface coating, stainless steel nails are preferred, rather than plated steel, because galvanising or other plating can be damaged when the nails are driven home, leading to corrosion. With annular ring shanks nail penetration into the battons should normally be 2.5 times the thickness of the board being fixed.

Secret nailing with single nails is not recommended for tongued and grooved boards because of the risk of the tongue splitting. Vertical overlapping boards 100mm wide or above should be double nailed. Nails should preferably be located at quarter points in the board width, but it is important that where boards are overlapped, or in a board-on-board pattern, that the nails fixing the outer boards do not penetrate the inner boards, as this can lead to splitting of these boards.

Overlap - Vertical Board on Board Cladding

It is advisable that the natural tendencies of the board to change shape due to moisture variation are taken into account. Quarter sawn boards have the least risk of changing shape as they dry, but it is generally uneconomic to use quarter sawn boards only. For most types of cladding, any boards in which the growth rings run tangentially to the section, should be used heart-side out. However, with board-on-board cladding there is some advantage in using the inner boards heart-side in as this will give better contact between the inner and outer boards if the boards shrink. An overlap or open-jointed cladding design is more tolerant of movement than rebated or tongued and grooved profiles. If there is any distortion of tongued and grooved boards it may even make it difficult to engage the tongues in the grooves during installation and any subsequent movement can result in the tongues splitting off. If tongued and grooved boards are to be used, the width of board should be further restricted and only kiln dried wood at the recommended moisture content should be used.