Section 6.1.9
Stepped Cavity Tray
To minimise the risk of water ingress below an abutment, preformed cavity trays should be used where the roof meets the main structure.
The primary cavity tray requires two stop ends and a weep hole.
Use a profile or template of the roof to allow for accurate installation of the step cavity trays.
Take from the position of the roof truss, an additional depth measurement of the thickness of the roof batten, the roof covering and a minimum 65mm water mark for the lead covering.
The cavity tray must follow this guide as demonstrated, breaking the bond of the brickwork to allow for accurate installation.
Small pieces of brick should be used to ensure brick bond is not broken throughout the rest of the structure.
Cavity trays are laid on a thin bed of mortar with a minimum of 25mm raked out at the face to allow for the installation of the lead covering.
Where ever possible look to build proprietary horizontal and stepped cavity trays with lead work already attached.
The same principles applies when using render.
Convert to brickettes to allow for installation of cavity tray.
Ensure that the weephole in the design is used and positioned to allow for the thickness of render.
