Diagram showing an external wall with water repellent treated cladding and sarking (liquid impermeable vapour permeable) behind it to stop moisture from outside.Sarking is a waterproof, vapour-permeable, flexible sheet material. It is fixed directly behind timber cladding or under flooring material.

The purpose of sarking is to direct any water that may have penetrated the cladding back to the outside of the structure. It also provides a draughtproof barrier to keep wind-driven rain or dust out of the wall cavity.

Sarking is not a substitute for well-chosen and properly installed cladding. It should never be regarded as the principal means of weatherproofing.