Sarking Slate Roofs - Waterproofing & Insulation
Sarking is a term originating from the UK that was used to describe boards that slate was fixed to - as in "sarking boards". These days, sarking has a more general defintion e.g. "The foil sheet used in roofs to assist with preventing water intrusion; generally in high winds" or "A layer of boarding and/or a layer of waterproofing material fixed underneath the roof tiles".
Sarking may also combine insulation properties with its function as a waterproofing material. There are various product names and grades for sarking materials commercially available in Australia.
According to Standards Australia (www.standards.org.au ), sarking should be used on all roofs exposed to wind velocity in excess of 47m/sec (AS4200.2). Sarking prevents roof damage caused from droplets of water being driven up under the slate at high velocity. The application of sarking will depend on roof pitch, rainfall and wind velocity. Most architects and builders recommend sarking be used under slate providing it is (1) not too close to the slate under-surface (sometimes cross battens are used to create a larger air cushion) and (2) it is not stretched too tightly and allowed to sag slightly so that droplets of moisture fall between, rather than on the rafters.