Cavity Trays Ltd –  higher resistance specification solution

The impact of wind-driven rain on roof/wall intersections can be significant. A critical consideration therefore, is how to flash these intersections and to what extent they will be able to perform and maintain functionality with undulating pressure variances around the top of a building.

Driving rain accompanied with wind will breach a conventional running stepped flashing where pressure forces the water into the leading edge of the flashing. Once under the leading edge, water is immediately in contact with the back of the flashing and the (outer skin) fabric of the building, which becomes an internal wall below the roofline.

Running stepped flashings cannot provide the level of protection enjoyed by the alternative: individual stepped lapping flashings. But most importantly, it is how such individual flashings are shaped, lapped, positioned and secured that dictates their capability.

Preformed Type X Cavitrays from Cavity Trays are manufactured specifically for stepped and staggered gable abutments and have individual stepped lapping flashings already attached. The flashings are shaped to suit the angle of the roof, and following building-in of the Cavitrays, require dressing only.

The relationship between individual tray flashings provides an overlapping arrangement wherein should water drive under the leading edge, it is arrested by the underlapping layer and safely discharged away from the masonry area that remains protected. The flashing choices include lead, copper and synthetic options. All flashings are factory bonded onto the Cavitray via a bosem jaw, the most effective anchoring medium of all options tested by the Company.

The tray itself has a self-supporting cavity upstand, that transverses the cavity and terminates against the inner skin. It does not require support to hold it to shape, so the inner skin can be blockwork, brickwork, timber-frame, SIPS, etc. Additionally, the upstand is hinged so adjusts to suit the as-found cavity width, as opposed to the as-intended. Compatibility every time.

Cavity Trays has a history dating back to the 1920’s, and is the only cavity tray manufacturer awarded European Technical Approval. Manufacturing over 400 different tray designs including preformed trays for concave and convex walls, the Yeovil-based Company offers an appraisal service and a bespoke manufacturing service. Its products benefit a performance warranty.

A spokesperson for Cavity Trays Ltd commented “The use of preformed trays in cavity wall construction can ensure best practice build details are present and consistently formed, every time. Preformed tray volumes have increased since the NHBC announced they should be used for all complicated junctions and similarly, commercial schemes are making greater use of preformed trays, recognising the practical and financial advantages of so doing. Cavity Trays Ltd continues to invest in research and development of its products that are approved for use in the UK and Europe.

Cavity Trays Ltd, Yeovil, Somerset, BA22 8HU
www.cavitytrays.co.uk