Level Threshold Cavitray (Threshold Isolation DPC)
Type LTT Level Threshold Cavitray (Threshold Isolation DPC)
The new British Standard BS 8102 released in December 2009 provides the Code of Practice for the protection of below ground structures against water from the ground. Section 6.2 states waterproofing protection falls into three classifications:
1 – Barrier protection.
2 – Structurally integral protection.
3 – Drained protection.
A new preformed dpc tray has been launched (by Cavity Trays Ltd) to make easier the integration of elements at level thresholds and in so doing address the above new Standard.
The Level Threshold Tray (Type LTT) whilst technically a cavity wall dpc, performs twixt levels below and above ground. In so doing it embraces the three qualities above, promoting combined protection as highlighted in BS 8102, 6.2.2. Cavity masonry is able to drain conventionally yet be isolated against damp transference whilst permitting interfacing with the adjacent structure.
The Level Threshold Tray (Type LTT) provides an effective way of isolating both external and internal threshold skins to great advantage:
The Type LTT can be introduced to either one or both skins of a cavity wall. It encapsulates the threshold masonry so the transmittance of damp from the exterior skin inwardly or from the inner skin upwardly is prevented regardless of the manner the flooring is interfaced.
The Type LTT is manufactured in solid polypropylene dpc and is available in a range of sizes to suit the dimensions of all standard openings. If you happen to be building to a non-standard dimension, a bespoke service operates.
The Type LTT acts as a threshold dpc, and also extends downwardly over both faces of the masonry. At either end of the tray the protection rises, and wraps around the reveal masonry*.
In isolating one of the areas most susceptible to damp transference, the Type LTT permits abutting flooring, abutting insulation and dpc’s / membranes to continue over an inner skin and converge with an exterior skin that itself is isolated from dampness at the point of convergence.
Importantly, the Type LTT also regularises the manner in which the vertical closing of the reveal interfaces. It is compatible with proprietary Caviclosers and together they provide a systematic and consistent approach to construction of openings within cavity walls. Given that the merging of reveal protection with floor and sill dpc’s can be problematic, the LTT is the first product to provide a standardised solution in the form of a preformed cavitray.
Once bedded on the inner skin, the Type LTC requires no further attention. Interfacing may proceed.
The same applies with the external skin, where no further work is required of the mason unless the arrangement calls for the dpc to rise up behind the sill in which case an accompanying optional attachment strip is applied.
Aesthetically the installation may be finished off on the external face in several ways:
The visible downward projecting section below sill level can be left in position to interface between any abutting paving or ramp.
Alternatively it may be removed along a separation indentation just below the sill, leaving a small protective bedding lip, as highlighted within BS5628 A.184.108.40.206.
With regards the externally visible end wraps, these are beneficial as they challenge any wind-driven rain (pooling at the threshold level) where masonry and entrance paving/ramp surface meet. Following installation of the frame, the wraps may be trimmed to some extent at either side of the opening, – pending the sill profile.
The name: Level Threshold Cavitray might be considered a misnomer, as it can actually be used in most styles of threshold. It provides a systematic way of protecting thresholds and in so doing reduces risk. The bedding of Type LTT trays to both skins also expands integration options of the designer.
Product name: Type LTT Level Threshold Tray
Purpose: Isolates threshold masonry and permits integration options.
Material: Solid polypropylene dpc.
Manufacturer: Cavity Trays Ltd Yeovil Somerset UK BA22 8HU
Cavity Tray Standards