Parapet DPC stepping inwardly results in damp internal wall

The company recommends its Type P self supporting cavitray as a safe solution, designed to improve the structural stability of a cavity parapet whilst preventing any staining on the front elevation.

The cavitray is built into the inner skin and has a downward spanning section that crosses the cavity and exits against the inside face of the exterior skin, allowing it to remain unpunctuated as the preformed cavitray does not project through it.

The Type P projects through the inner skin downwardly to form a turn-down exterior lip, providing weathering cover to the bedding course of the cavitray and protection in areas where the roof flashing unites under the tray.

Building into both masonry skins to provide support to cavity spanning DPC’s was introduced as there were few alternative ways to hold a soft or pliable DPC in place, however Cavity Trays warns that the practice can cause structural issues when the DPC is exposed to high levels of wind pressure.

Parapet DPC’s at a high level that step inwardly allow for water to under track the supported DPC and trickle towards the inner skin of the cavity parapet below roof level, resulting in significant damage to the internal wall.