Preformed cavity trays running parallel with the roofline are incorporated in the masonry where a gable abuts a cavity wall. In the case of brickwork, standard 75mm coursed trays are used. But where the walling material is of different coursing, different depth or built against a backing block, an alternative approach is required.
Multicourse cavitrays are manufactured by Cavity Trays of Yeovil and are available in an infinite combination of dimensions to suit the walling material being used to build the gable.
Trays are first sized to match the course height. The cavitray layout must provide continuous unbroken protection throughout the slope. The finished installation is best described as a dpc staircase. The tray base being the stair tread and the tray end upstand being the riser. Masonry above the tray line will be exposed to the weather but the staircase of trays prevents dampness from continuing permeation downwardly.
The depth of each tray accommodates the entire outer skin of masonry. This includes any backing block against which the outer skin is being raised. Once the tray base reaches an appropriate position in the cavity it rises upwardly, to provide protection across the cavity width. This upstand is actually hinged so it can span the as built cavity width as opposed to the as intended.
As the flashing is already attached to every tray, the usual task of raking out joints and cutting/fitting separate flashings is eliminated. Having the flashings attached also means there is no need to return to point-in afterwards.
Cavity Trays will schedule all requirements and provide the complete solution for all abutments. Multicourse cavitrays benefit a performance warranty and are supplied labelled and ready for immediate installation by the mason.