External Cavity Wall Moisture Management

if the wall is an external cavity wall (see Diagram 6.2), the cavity should be taken down at least 225 mm below the level of the lowest damp proof course, or a cavity tray should be provided to deflect penetrating water towards the outer face so as to prevent precipitation passing into the inner leaf. Weep holes should be provided every 900 mm to assist in the transfer of moisture through the external leaf. A cavity tray may be used where a cavity wall is constructed directly off a raft foundation, ground beam or similar supporting structure and it is impractical to continue the cavity down 225 mm.