Type X Cavitray (Cavity Trays Ltd)

   designers'
   comments

    The original code of
    practice 121:101:1951
    showed a cavity DPC
    arrangement with a 75mm
    upstand. We always
    considered this far too
    small an upstand in our
    experience for new work
    applications. Eventually
    the new code of practice
    revised the upstand
    height to 150mm, a
    dimension which is now
    prominent in BS5628 and
    BS8215:1991.
    However, it is interesting
    to note that not all
    manufacturers produce
    to this stipulated height.
    Type X cavitrays have
    always been produced
    to this dimension, prior to
    any BS enforcement,
    following our own
    evaluation. Tests have
    also established that
    water can be forced
    under some damp-proof
    courses constantly high
    pressure differentials
    exist. Thus the
    requirement for all trays
    to be bedded on mortar
    to achieve solidity of
    bond and to ensure
    wind-driven rain cannot
    penetrate beneath same.
The base of every Type
    X cavitray us unique as it
    incorporates water bars
    which act as drips to
    prevent discharge
    run-back.

use
Preformed cavitray complete with integral lead flashing, to form a stepped cavity DPC and flashing at the abutment of a pitched roof with a cavity wall.

introduction
Every stepped and every staggered gable abutment must be so constructed to prevent rainwater and dampness from penetrating below the abuting roof line. This is because the external skin changes status below the roof line and becomes an internal skin. Accordingly, any preformed system must meet three basic requirement:
1 It must prevent dampness from penetrating below the critical stepped roof line.
2 It must extremely weatherproof and flash the physical roof/masonry intersection.
3 The arrangement must always protect the inside skin also from becoming damp. The high performance Type X cavitray fulfils all such functions, whilst speeding up operations on site and ensuring a good and known quality of build.

type X cavitray
Type X cavitrays combine the functions of cavity DPC and roof lead flashing. Tray installations is very straightforward and in a typical brickwork application the bricklayer lays one tray in every course, following the slope of the roof. All trays and the projecting lead flashing are flush-pointed as the masonry is raised. Thus the usual requirement to rake-out joints and return to point-in flashings at a later date is eliminated.
The bricklayer having built-in the trays whilst raising the wall has completed his work.

Trays are manufactured with two choices of lead flashing lengths. Short lead flashings are suitable to dress over the upstand of a secret gutter or soaker. Alternatively, long lead flashings may be dressed across the roof tile. Under such circumstances, roof tiles must be suitably 'shaped' (ie: not flat). At a later date when the roof surface is complete, the plumber has only to dress the flashings.

cavitrays suit all cavity widths
Type X gable abutment cavitrays incorporate an adjustable hinged back upstand which is rigid and

self-supporting. Accordingly, upstands do not require building into the inside skins.

The cavity upstands automatically adjust to suit the cavity width in question. This is a most important consideration when one appreciates that the as-built cavity width is not always the as-intended cavity width.

The standard Type X cavitray will suit cavity widths from 50mm up to and including 140mm automatically. This feature also eliminates the necessity to raise both skins of the cavity wall together, thus overcoming the problems experienced with some systems which rely on course levels with both skins always harmonizing.

course sizes
The standard Type X cavitray is designed to suit standard brickwork with approximately 75mm courses. Type X cavitrays are also supplied to suit other walling materials such as reconstructed stone courses, blockwork courses, modular blocks, etc. Please refer to separate pages.