Cavity Trays Ltd

 Type P Cavitray
for parapet walls

in brief...

  • DPC integrity regardless of wind direction
  • Enhanced parapet structural stability
  • Takes up cavity variances
  • Unobstructed cavity compartment area

use
To weatherproof parapet walls.

introduction
The function of a parapet wall cavitray differs form that of a conventional tray, because both skins of a cavity parapet are outer skins, and accordingly accept moisture.  The purpose of any parapet DPC is to prevent rainwater travelling down the exposed inside skin, which becomes an internal wall below the roof level.  The preformed Type P cavitray is designed to overcome this problem.

type P cavitray
The Type P cavitray is a rigid horizontal DPC, manufactured in long lengths.  Preformed angles enable the complete installation of 

 

 

a parapet damp-course to be carefully planned and controlled.  It is self-supporting and requires building-in to one skin only.  Accordingly, the structural stability of the parapet is enhanced when compared with parapet standard details and related problems.  Water collected within the cavity can discharge against the inside face of the building's exterior skin.  Penetrating water therefore discharges regardless of the direction of the prevailing wind or rain, whilst also permitting the cavity to breathe.  The likelihood of interstitial condensation, common to many parapets, is thus reduced.

 


 Such a preformed damp-coursing method is not possible with traditional lead, felt or polymer materials, which sag, being soft and unsupported across the cavity.  These materials are forced to adopt a diagonal line in crossing the cavity, with the upper and lower edges secured within the mortar beds.

sizes
2400mm x 25mm lip x 110mm x 150mm cavity drop Angles 450mm x 450mm

material
2mm securtex finished tensioned polypropylene.

colour
Black

installation/sitework
Product should be built into masonry observing usual requirements of laying damp-course.  Incorporate lead flashing to inboard side.  Full instructions accompany all supplies.

bill of quantity
wording
Type P cavitray from Cavity Trays of Yeovil, Somerset BA22 8HU (01935) 474769.  Lay preformed Type P parapet cavitray lengths and angles within appropriate mortar bed as work proceeds.  Clove lap and seal adjoining lengths.  Incorporate roof lead flashing to detail.  





 Observe accompanying fitting instructions at all times.
Metres run including overlaps
= ................... No of angles
= ...................

building regulations
Building Regulations, British Standards and NHBC requirements may be satisfied with use of this product.  See page listing references.

ordering
See inside back cover for immediate service throughout the United Kingdom.  Merchant distribution network.

related products and
applications
For parapet closer and DPC support, see Type J.  For parapet DPC, see Caviroll.  For ventilation at high level of a parapet, see Type W.  Lead flashing for dressing over the roof upstand is listed under Lead Fabrications and Supplies.

      
   designers'
   comments
    
    Type P was originally 
    subjected to much 
    criticism because it 
    promoted the crossing if 
    the cavity outwardly 
    rather than inwardly.  
    Tests indicated the 
    outward stepping profile 
    was safer - and 
    eliminated the possibility 
    of water tracking on the
    underside of the profile.  
    It is interesting to note 
    that the outward profile
    is now the only parapet
    profile featured within
    BS8215:1991. 
    Furthermore, BS5628-3.
    2001 within 5.5.7.10 
    states: "it should be
    noted  that the DPC or
    cavity tray structurally
    separates the
    parapet from the wall 
    beneath, and the coping 
    from the parapet.  
    Structural stability of the 
    parapet should be 
    considered in
    accordance with
    18.4.1."  This 
    reasoning underlines our
    tensioned profile, which 
    steps outwardly yet 
    enhances parapet 
    structural stability as the
    external leaf is not 
    interrupted.  Parapets 
    normally have a stress 
    factor of less than 
    0.1N/mm˛.

   technical 
   observations
   All dimensions including 
    cavity size suitability,
    can be altered to suit a
    client's requirements.
    Eliminates danger of
    underside water
    tracking associated with 
    up-turned profiles.  
    Branded with name and
    logo as proof of type and
    accompanying warranty.