There is always a risk that water can penetrate the external leaf of a cavity wall and find its way into the cavity. This risk is greater in geographical areas that are exposed to harsh weather conditions and/or where a more porous brick has been used for the external leaf of the cavity wall. As the
cavity exists as a moisture barrier, it is vital that water does not cross the cavity and penetrate the internal leaf of the cavity wall.
Fig. 190 Examples of plastic weephole inserts.
Fig. 191 Plastic weepholes inserted above a door opening.
Wall ties are provided with a ‘drip’ to ensure that water falls off into the cavity and all bridging points across a cavity such as lintels and airbricks are provided with a DPC tray, which deflects water back towards the external leaf. Another bridging point is where the cavity is filled below ground with a lean mix of concrete and finished with a sloping surface (towards the outside), at finished ground level. Around the base of a building, weepholes should be installed and horizontally spaced every 890mm. Above cavity trays over the tops of door or window openings, they should be spaced every 450mm.
Traditionally, to form a weephole, an open cross-joint would be left, but this tended to look untidy, was sometimes ineffective if the open joint was not completely clear of mortar, and also often got forgotten anyway. Nowadays, proprietary plastic inserts designed to fit into a cross-joint provide a much more satisfactory solution. They are available in a range of colours, to tone with the bricks being used.