Options now increased within 2011/2012 technical manual
When building-in a stone or precast sill, there is an accompanying requirement to prevent damp ingress, where the sill closes or impinges the cavity.
By using a preformed dpc Undersill tray this task can be simplified and at the same time thermal and acoustic qualities can be maximised.
The Type U Undersill Cavitray by Cavity Trays of Yeovil is available to suit both solid sills and sills formed on site from brick tile or stone.
There are versions for traditional construction and timber frame construction.
When used for site-formed sills the Type U Cavitray acts as formwork onto which the sill is constructed.
The projecting sill front is aligned against the front upturned edge of the tray that acts as a guide.
Once the sill has cured this upturned edge is removed along a separating line, leaving a visually unencumbered sill externally but protected and enveloped internally.
With solid sills the Type U Cavitray encapsulates the sill on three faces and projects downwardly to ensure no tracking inwardly of penetrating water can occur.
The cavity face of both styles of Type U Undersill Cavitray can incorporate a bonded acoustic and thermal isolation strip that permits contact with the inner leaf without compromising the isolation qualities.
In the case of timber-frame construction the tray design additionally includes provision to accommodate some differential movement.
This is necessary because of the differing expansion and contraction rates between timber and masonry.
As the cavity width grows wider all sills can be subjected to greater rotational pressures because of the see-saw effect.
Type U sills are available to suit the customers desired sill deflection angle and dimensions.
The designer is not limited to popular permutations only offered by alternatives and Cavity Trays Ltd will be pleased to provide assistance.
See pages 49, 50, 51 of new 2011/12 Technical Manual for details.