This article gives very general guidelines for applying horizontal external cladding. uPVC and fibre cement cladding materials usually come with their own instructions and include trim pieces (i.e. end sealing strips etc) specific to the manufacturer.
This article is intended for the UK use, other countries will probably have their own building codes which will need to be conformed to.
Timber building materials should never be placed in direct contact with soil or used at a level which may be flooded.
Cladding should always stop some 15cm (6 inches) above ground level, whether it is concrete or soil, this reduces the amount of muck splashed up to them from rain hitting the ground.
The bottom of the lowest plank should ideally be cut at an angle to form a drip line along the front of the lowest plank (see right)
Timber plank sizes
The different plank profiles (see this other article) are usually available in a choice of widths ranging from 200 to 225mm (4 to 9 inches) - the different profiles will have a different choice. The wider the planks (which also generally means thicker), the greater the problem with warping and twisting - 150mm (6 inch) wide planks are often considered to be the widest preferred width.
Generally, the longer the length of cladding, the wider planks look better (the converse is also true, the shorter the length, narrower planks look better) - but there are no hard and fast rules.
Wherever possible, a single plank length should be used across the full width; joints in a horizontal run should be avoided as they offer a route for water to enter behind the cladding. Where planks have to abut horizontally, they must meet in the middle of a batten,
Vapour barrier membrane
Where the supporting wall is not weather tight (i.e. timber frame) or where insulation is to be fitted behind the cladding, a vapour barrier must be fitted to cover the wall or insulation material.
This prevent any moisture which does get behind the cladding from penetrating the building structure.
In the UK, the vapour barrier membrane should comply with BS 4016.
Timber battens should be fitted vertically to the building to support the cladding, the battens should be pressure treated softwood, typically of minimum size 25 x 38mm (1 x 1½ inch) - the thickness of the battens should be at least 1½ times the thickness of the timber cladding to ensure they are thick enough to take the fixings (where overlapping cladding planks are used, this means 1½ time the thickness at the overlap).
Battens should be fixed vertically (either nailed or screwed) on top of the vapour barrier to the structure, the horizontal spacing between the battens should be no more than 60cm (2 ft).
A horizontal batten should be fixed just above the bottom line of the cladding to close off the space behind the cladding - this denies entry for pests and small animals.
Where the cladding is to be put onto a gable end, a batten should be fixed parallel to, and just in from the gable lines. In a similar manner with a sloping roof, a batten should be fixed parallel with the roof line.
As battens are being fixed, each one should checked to ensure that the front face of all are level horizontally and vertically, small pieces of treated timber may need to be fitted behind some battens as packing to overcome irregularities in the wall. It usually helps to start by fixing the extreme end battens, and then using a line stretched between them to line up the front faces of the remaining battens.
There are three possible ways from cladding planks to end:
- A stop, either where the cladding stops at a point where it abuts a return or just where the cladding stops.
- An external corner where the next cladded face goes away backwards from the corner
- An internal corner where the next cladded face comes forward from the corner.
Each of these is illustrated to the right; the method for 'closing' each is:
- A vertical piece of timber is used to close off the end of the cladding, either in front (as illustrated) where the cladding meets a return, or down the side where the cladding ends.
- At an external corner, a vertical timber should abut the end of the cladding on each side face.
- A vertical timber should be fixed before the cladding is applied so that the cladding on each sides buts up to it.
Cladding planks can generally be nailed to the battens, usually there is no need to pre-drill - but pre-drilling pilot holes may be needed with hardwood cladding or for the nails near to the end of the planks to reduce the chances of the timber splitting.
Fixing nails should be at least 2½ time the thickness cladding, including any overlap
Avoid using steel nails, instead use hot galvanised dipped, marine quality or other non-corrosive nails. Using annular ring nails will hold the cladding more securely but are generally unnecessary.