The masonry leaf of the external wall is often permeable to wind-driven rain and other elements and may allow the ingress of water. A ventilated and drained cavity between 40 mm and 60 mm thick is installed between the masonry outer leaf and the timber studwork to permit the escape of water and prevent the likelihood of condensation. It is important that the cavity width be properly maintained so that the performance of anchor straps, wall ties, etc. is not affected. Ventilation is achieved through the installation of proprietary vents installed into the perpends of the masonry outer leaf.
The proprietary vents are located at 1.5 m centres both at high level at the eaves/verge, and at low level below the DPC, where they also act as weep holes. It is for this reason that the cavity must be kept clear of debris from construction (e.g. mortar, timber). Proprietary vents located below the DPC level also act as weep holes.
