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Caviclosers and Cavitrays – Specification Adherence is Important

Author/Issuer: Cavity Tray Standards    Added:

Part L has focussed attention to detail on site and an understanding of how and where thermal transmission losses occur. Both ventilation losses and fabric losses must be addressed.

Thermal bridging commonly occurs wherever a cavity wall is punctuated by a window or door opening. But construction methods have changed, and it is now possible to construct such openings in a different manner. One can abandon using conventional DPC and conventional DPC methods when constructing common openings within cavity walls. Instead, by using a multi-functional vertical caviclosers, one can enjoy considerable benefits and satisfy the regulation demands including Part L and the accompanying trend to introduce a wider cavity.

Closers of various shapes and sizes have been available for many years, but the latest models can offer an additional quality – fire integrity. A specification enhancement that is desirable at all times whilst being essential within certain constructions and those of multi-occupancy. With cavity widths becoming wider, there are now new models to suit cavities as wide as 200mm.

The advantages of using a preformed cavicloser are numerous:

  • 1)  It physically closes the reveal. There is no need to cut and return blockwork at 90°.
  • 2)  It acts as a vertical DPC, so conventional roll DPC is not required.
  • 3)  It insulates the reveal, thus addressing the requirement to reduce thermal bridging.
  • 4)  It permits a variety of frame positions within compliant parameters.
  • 5) Finally, use of the right preformed closer can result in the construction benefiting resistance against the spread of fire.

The Cavi 60 Type WCA is an example of a multi-functional cavicloser.  The Cavi 60 prefix signifies 60 minutes fire integrity rating whilst the WCA stands for Wide Cavity Applications. The robust profile acts as a DPC and is filled with a rock-based mineral insulant. The reveal face benefits anti-capillary veins to interrupt the natural water ingress path whilst allowing the building designer a variety of frame positions within the compliant parameters. The Cavi 60 Type WCA is available to suit any specific width up to 150mm maximum and has been independently tested.

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The Cavi 60 Type WCA.
Cavi60 signifies 60 minutes fire integrity.
WCA stands for wide cavity applications.
This model is available for cavities up to 150mm wide.
Caviclosers are available from Cavi 60 up to Cavi 240 (four hours) rating.

 

Every time a roof surface finishes against cavity masonry the wall must be constructed in such a manner that everything below the roofline is isolated against permeating dampness.

The task of keeping out the wet originally involved lots of dpc material being cut and laid in every course immediately above the roofline. The dpc would then rise up in the cavity and be built into the inside skin. This was accompanied with much folding and bending of the dpc to seal the inboard end.  Flashings were then cut out from a roll of lead and wedged into the masonry under each dpc. The result was generally inconsistent and necessitated several trade visits including a final one to point-in the flashings. All in all the exercise involved considerable labour, materials and much wastage.

One also had to keep ones fingers crossed the now hidden pointed flashing /dpc union was watertight.  One mistake, anywhere, could result in the arrangement failing.

In comparison there is now an-off-the shelf method of achieving perfect gable abutment integrity. The Type X cavity tray for sloping roof intersections is manufactured by Cavity Trays of Yeovil, the only tray manufacturer in Europe awarded European Technical Approval.

The Type X is a ready-moulded dpc cavitray that provides the perfectly shaped unit for building into the masonry. The cavity upstand on each tray is self-supporting with a memory-hinge that takes-up whatever cavity width is encountered on site. Being self-supporting means it does not have to be built into the inside skin. It makes the tray ideal for use with both traditional and timber frame construction. The wider cavities encouraged by Part L are automatically accommodated, as are unintentional variations or deviations in width! Each Type X tray has its own attached lead flashing which is pre-shaped to suit the angle of the roof.  The tray is simply bedded and flush-pointed as the wall is raised. There is nothing more to do other than dress the flashings at a later date. You can choose short flashings if you have flat tiles or slate, or long flashings if you wish to dress them directly over contoured tiles. The result is an easier, better and consistent way of joining roofs to walls.

The self-supporting memory hinge means there is no need to build into the inside skin – which remains undisturbed so air leakage issues associated with interrupted block work does not arise. The Type X cavity tray is accompanied with product liability protection for the benefit of Architect, Builder and Client. The trays can be used to satisfy the regulation requirements including applications with wider cavities as promoted within Part L. Cavity Trays of Yeovil stands alone in being the only tray manufacturer awarded European Technical Approval.

Type X Cavitray from Cavity Trays of Yeovil
Type X Cavitray from Cavity Trays of Yeovil

 

 

Type X Cavitray with ready-shaped lead flashing.
Note the cavity upstand is hinged and self-supporting and adjusts to suit cavities up to 140mm wide.

 

Extract from Specifer Profile, article by Peter Roper

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