The installation of cavity trays at this critical junction are not being formed correctly, with warranty surveyors noting a range of issues, typically:

• Incorrect positioning
• Cavity trays terminating behind waterproofing or flashing upstands
• Lack of weep vents/holes to facilitate expulsion of water from the wall cavity
• Lack of raking out leading to grinding out of mortar joints and damage to cavity trays

Our concerns also extend to the lack of planning to avoid the issues and solutions that are often presented to warranty surveyors to close out such defects, which are often falling well short of the expected levels of performance required for warranty.

Our stance is that the correct linking of the cavity tray with the horizontal cover flashing is critical, and that the cover flashing must sit directly underneath the cavity tray.

Failure to provide this is considered to compromise the ability of the wall and roof construction in meeting with the functional requirements and performance standards stipulated by the Technical Manual, notably those relating to the avoidance of water ingress into the building.

Developers need to ensure that site teams and sub-contractors installing cavity trays and flashings above horizontal abutments, are fully aware of the requirements for this critical detail.

In order to achieve this correct linking the cavity tray must be bedded on a thin bed of mortar, which is then raked out prior to the mortar curing, this is all in order to allow the cover flashing to be installed correctly underneath the cavity tray.

During their inspections of on-going work on site, the site team and any appointed supervision for the work packages should be ensuring that:

• Bricklayers are setting out to the correct height – 150mm waterproofing upstands to these locations are required – so cavity tray heights should be set accordingly.
• Bricklayers are raking out of the thin mortar bed below the cavity tray to allow the flashing to be dressed under its location by the follow-on trades.
• Bricklayers/roofers are not grinding out the joints after the mortar has cured and risking damage to the cavity tray.
• Leading edges of horizontal cavity trays are visible on completion over any such roof abutments – do not conceal the leading edge with mortar.
  Any sealing work using lead sealants or sealants that form part of the roof waterproofing system should terminate under the cavity tray and not conceal its position.
• Weep holes should be present at the correct centres, be of the correct type for the wall construction and not blocked.

For further information about cavity trays and detailing, please refer to the ‘External Walls’ section of the Technical Manual.