The level threshold is an everyday feature in construction that can be problematic. It is not just marrying of the external and internal levels that can prove challenging, it is doing so in a manner that protects against wetness permeating and permits a functional interfacing with the method of reveal closing/insulation and the oversite membrane.
There is now a new product manufactured specifically for this purpose. It regularises this specific area of construction. It permits internal and external floor levels to interface at an opening within a cavity wall.
Cavity Trays of Yeovil has come up with a Level Threshold Tray (Type LTT). It provides an effective way of isolating both external and internal threshold skins to great advantage:
Type LTT details
The Type LTT 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 with the tray.
The Type LTT is manufactured in solid petheleyne 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 additionally 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 dpcs/membranes to continue over an inner skin and converge with an exterior skin that itself is isolated from dampness at the point of convergence.
The oversite membrane is able to terminate against the Type LTT and maintain functional integrity. Importantly, the Type LTT also regularises the manner in which the vertical closing of the reveal interfaces. It is compatible with Cavity Trays' range of Caviclosers, and together they provide a systematic and consistent approach to construction of openings within cavity walls.
After Being Bedded in Position
Once bedded on the inner skin, the Type LTT requires no further attention. Interfacing may proceed. The same applies with the external skin, although the following options apply regarding how the installation is finished off on the external face:
Externally, the visible downward projecting section below sill level can be left in position to interface within the gap provision 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.220.127.116.11.
*With regards the externally visible end wraps, these are beneficial as they challenge rain pooling at the threshold level from permeating where masonry and entrance paving or ramp surface meet. Aesthetically these wraps may be trimmed to some extent at either side of the opening, following installation of the frame - pending the sill profile.
The name: Level Threshold Tray 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 removes risk. It has already been identified as a welcome solution to anyone who has had to address a problematic entrance arrangement or remedy an existing opening.
Permits floor finishes to interface
Sizes for all opening dimensions
Ready-shaped solid petheleyne DPC
Interfaces with vertical closing
Addressing Standards Both Above and Below Ground Level
A new British Standard was released in December 2009. BS 8102 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:
A Barrier protection.
B Structurally integral protection.
C Drained protection.
The Type LTT Level Threshold Tray whilst technically a cavity wall dpc, performs twixt levels below and above ground. In so doing, it embraces the qualities of A + B + C, 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.
Manufactured: from solid petheleyne dpc.
Opening sizes: Over twenty sizes to suit all standard opening dimensions and thicknesses of masonry skin.
Bespoke option: Tailor-made service operates for non-standard dimensions.
Average lead-time from receipt of order is three days.
Available from 1st February 2010, throughout UK, Ireland, Netherlands, Belgium.
Associated Further Reading/References
Building Regulations Approved Document C
NHBC chapters 5 & 6