The exterior skin of a cavity wall is designed to become wet when rain falls. The cavity prevents that wetness from reaching the inside skin. Wherever the skins connect at lintel level, a dpc tray ensures the penetrating water is prevented from reaching the inside skin. Similarly all wall ties are shaped so water tracking along a tie drips off it into the cavity before it reaches the inner skin.
The attachment to an existing exterior skin of an extension results in the original exterior skin becoming an internal wall below the new roofline. If the abutting roof is flashed only, there is nothing to prevent the penetrating wetness from gravitating downwardly into the new extension.
The solution is to install cavity trays. The only cavitray awarded European Technical Approval and designed for insertion into existing walls is the Type X manufactured by Cavity Trays of Yeovil. This approved tray has many novel features that make the task of installation and compliance easy, swift and economical.
The Type X cavitray has its own attached lead flashing, ready-shaped and secured within a protective bosem jaw. Once the tray is built-in, the flashing requires only dressing. The tray back upstand projects upwardly in the cavity and is memory hinged. It is designed to open to take-up the maximum cavity width it encounters. Thus, cavity compatibility is achieved every time. It is possible to install a Type X cavitray by removing only a few bricks. The upstand can fold to a horizontal position permitting the tray to be inserted into an opening of just one brick height.
Inserting a cavitray is not limited to just new porches, conservatories and general extensions. The Type X is also suitable for remedial applications where an existing dpc arrangement has failed.
Authorities regularly specify the Type X cavitray as the guaranteed approved replacement for where dampness persists despite an alternative dpc or system being in position. The performance undertaking given by Cavity Trays Ltd can provide peace of mind for architect builder and client.