For most cladding softwoods, small headed ring shank nails are used but for Western Red Cedar larger heads are recommended to avoid the potential for nails being pulled through this low density species.
On all hardwoods and some higher density softwoods e.g. Siberian Larch, Douglas fir, the use of screws is recommended. For these dense species (and on other species if any potential for splitting around fixing points is to be avoided), the pre-drilling of screw fixing pilot holes 2mm oversize should be carried out to allow for any movement in the board that may occur after installation. On green oak, it is important to use oversize (4mm minimum) fixing points with washers or fixings with larger heads to take up the shrinkage that will occur.
Pneumatic fixing guns should be used with care to ensure the surface is not affected by impact damage or the fixings driven below the surface. Many fixings supplied for gun application come with off centre D shaped heads and designers should satisfy themselves that this is aesthetically acceptable. For screw fixing, hand held “impact” type screw drivers are best as these are less likely to damage the wood or the drive recess and will insert the screw at optimum speed and prevent the coating burn associated with high speed power drivers.
All fixings should finish flush with the surface and should not be punched or countersunk because this can result in splits and surface staining. As such it is important to ensure that the cladding moisture content is around 16% at time of installation to avoid shrinkage that would leave fixings proud of the surface.
Where concealed fixing is required then boards may be back fixed to counter battens or installed using a proprietary metal fastening bracket or support system. Concealed fixing systems are best used in the prefabrication of cladding panels.