NHBC standards now state that a preformed cavity unit must be used instead of bending or folding DPC at complicated junctions, which was previously common practice on traditional housebuilding projects.
Changes of direction of a cavity tray or interfaces with other elements in the cavity are more complicated than simple joints and would involve complex bending, folding, or cutting and sealing if fabricated on site.
At complicated junctions, clear drawings and the design should be provided, and preformed cavity trays used.
Complicated junctions can include:
- Pitched roof abutments (i.e., stepped trays)
- Steps in horizontal levels
- internal and external corners
- T-junctions (ie, intersection of parapet wall)
- Door thresholds (in conjunction with gas membranes, flat roofing detailing etc)
- Penetrations in horizontal cavity tray arrangements (ie, telescopic vents, services etc)
- Interfaces with windposts, balcony supports, balustrading or guarding.
The benefits of Preformed Units:
- Off-site manufacturer – reduces the risk of water ingress.
- Three dimensional shapes – simplifies detailing at complicated junctions.
- Extensive range – suitable for both built-in and surface fixed cavity tray applications.
- Versatile – suitable for both damp and gas proofing applications.
- Multifunctional – compatible with all our damp proof courses and membranes.
Grayson can supply a full range of preformed units for all projects, whether these are from a High-Performance DPC or a Gas-Resistant DPC for traditional builds or non-combustible for taller projects.
Contact your account manager today on 01709 786100 and we will ensure you get the correct item for your job.