Compliant Cavitrays for Curved Cavity Walls
Curved cavity walls and spherical corners have in the past posed problems for designers requiring sloping roofs to converge with the shaped masonry, be it concave or convex. Wind-driven rain striking curved masonry will flow diagonally, causing increased water volumes to transverse across and around the masonry. As well as affecting the extent of localised rain washing over the surface of the masonry, curved cavity walls also change the behaviour of water and its permeation of the outer skin.
Sloping roofs abutting curved masonry must take into account the following;
The DPC within the cavity wall and the actual flashing change in shape and dimensions at every intersecting course. Whilst the pitch of the abutting roof may remain constant, the actual angle of intersection alters at every course as the wall turns.
One has to determine the optimum dimensions at each course so every tray integrates with the tray above it in a manner that is watertight and continuous, to create a protective ‘DPC staircase’.
Curved outer and inner masonry skins necessitate the protective DPC medium curves and shapes to match the radii of the masonry faces – conventional roll DPC cannot elongate or contract to achieve this.
If the DPC requires building-into the blockwork inner skin to provide support, blockwork 225mm coursing means there is not always a convenient or corresponding course available, being too high or too low compared with the brickwork outer skin course from which the DPC commences its rise.
Externally the flashing is required to act as a waterproof medium to link roof finish, wall and DPC. Creating a positive consolidated union between flashing and DPC within a mortar course can be difficult to achieve, especially in and around a curved skin.
Wind-driven rain will blow under the leading edges of stepped flashings where dressed against the masonry, and the increased volume of water-wash traversing a curved wall compared with that flowing over a straight wall necessitates measures are in place to manage this curved ‘windscreen effect’.
Cavity Trays of Yeovil has the solution.
It manufactures preformed individual curved components that address all the considerations above, resulting in an assured build detail, fulfilling Building Regulation requirements.
Each Cavitray is designed to exactly match the requirements at every intersecting course. These are called Type X curved Cavitrays and are based on the proven design awarded European Technical Approval.
The advantages of using preformed curved Cavitrays are numerous:
Fabrication on site is eliminated – there is no measuring, no cutting and no wastage. Preformed also means the shape is already determined – installer mistakes or oversights can be eliminated.
Each Cavitray has its own adjustable cavity upstand.
There is no requirement to locate and build into an inner skin course as upstands are self-supporting.
Self-supporting and adjustable also means each tray upstand can adjust to suit the ‘as-found’ cavity width, as opposed to the as intended. Compatibility is thus assured.
Additionally, at the inboard end of every tray there is an integral end upstand that rises within the masonry provide a vertical link with the tray above. Thus, as each tray is laid it integrates with the previously laid tray forming a DPC staircase – with connecting treads and connecting risers.
Where trays are supplied with the flashing already attached the traditional need to rake out joints and introduce flashings separately is eliminated. The union is pre-established.
Because each Cavitray and flashing overlaps the next Cavitray and flashing, wind-driven rain blown behind a dressed flashing leading edge does not come into contact with the masonry under (unlike conventionally cut running flashings). The overlap configuration provides a secondary layer to arrest such water, preventing it from permeating towards and downwardly beneath the adjacent sloping roofline.
Cavity Trays Ltd undertakes to calculate concave and convex abutment requirements / schedules for clients. Each tray is numbered and the mason has only to numerically build-in trays as the wall is raised.
Cavity Trays Ltd is the longest-established company in its specialised field and can claim a proven history dating back to the 1920’s. The Yeovil based Company operates a free design and advisory service and in addition to over 250 standard solutions, Cavity Trays Ltd operates a bespoke service with products being exported worldwide. Cavity Trays remains the only UK tray manufacturer awarded European Technical Approval with products accompanied with a performance undertaking for the benefit of architect, builder and client.
Specify clearly Cavity Trays of Yeovil to secure benefits and accompanying warranty.
T 01935 474769.