Sarking - Materials
Only vapour permeable building paper should be used. Sarking must be impermeable to moisture yet still allow the free flow of water vapour from the back surface of the cladding. If sarking restricts the flow of vapour, timber cladding that has taken up moisture in wet weather may tend to cup as the outside face dries.
Never use non-permeable materials, such as polyethylene film or foil as sarking immediately behind timber cladding. Perforated foil insulation should not be used as sarking immediately behind timber cladding.
Where board cladding is used it is good practice to use a vapour permeable sarking on the outside of studs and directly under the timber cladding.