Development schemes replicating past construction styles demand an innovative approach to damp protection over the window heads.
Cavity Trays of Yeovil has produced an option for the builder that provides warranted modern damp protection in the form of ready-shaped cavitrays that can be incorporated without being externally visible.
Timber lintels over external openings are currently popular where a traditional cottage style elevation is sought. The innovative approach is to build in the timber lintel so it is purely a visual element, and provide support via a steel lintel immediately above the timber. The steel lintel is of a longer length than the timber under it, so it bears and all loads subsequently bear on masonry. No structural demands are made on the timber under the steel that adopts a visual presence only. The arrangement also provides opportunity to introduce enhanced thermal insulation adjacent to the window head, so the opening can benefit higher overall thermal integrity (provided using sleeved insulation barriers also from Cavity Trays of Yeovil).
In such applications damp protection in the form of Type C cavitrays is provided at two levels. A Type C cavitray bedded on the steel lintel arrests most of the penetrating rain. Complete with stopends, this cavitray discharges the arrested water via discreet caviweeps incorporated towards either end the tray away from the window opening.
At a lower level under the timber is located a second smaller cavitray. This provides protection against water tracking inwardly in and around the timber lintel, acknowledging that eventually shrinking and settlement will occur where timber and masonry abut.
A company spokesman commented: We recommend the two level/two cavitray approach. It overcomes a common weakness that manifests if one positions the timber directly on a steel lintel. So doing results in all penetrating water being routed behind the timber where the water can pool as well as sponsor rapid decay. It also means all loading effectively rests on the timber first not an ideal arrangement given the circumstances.
Our two level/two cavitray approach avoids this hazard and no structural demand is made on the timber. And in the event the timber should ever require replacement, it can be done without affecting any load bearing aspects of the structure.
Type C Cavitrays are available in profiles and dimensions to suit all opening styles. Whether the requirement is traditional, modern or classical, there are preformed trays to protect the detail.
View Product guide: Damp-proofing, Closers, Membranes Volume 21 PDF