The NHBC has announced within its’ Technical Guidance 6.1/38 that from 1 January 2023 Polythene Damp Proof Course made to BS 6515:1984 will not be accepted over window and door openings on all plots starting or at DPC level on that date. The NHBC announcement aligns with the usage/restrictions stated within the British Standard, that qualifies such a DPC is not suitable where there is downward movement of water
An alternative way forward is to use a preformed Cavitray. When horizontal preformed Type C Cavitrays from Cavity Trays are used with lintels, one eliminates the variances of a site-fabricated approach. Preformed Type C Cavitrays are ready-shaped to harmonise with the window head construction/lintel choice, so the build detail is always consistent and always correct.
Type C Cavitrays are also self-supporting, which means they hold to profile and do not require building into the inner skin (unless you request otherwise). So, no seeking out a bedding joint at an appropriate height to hold up the protection. Full cavity width arrestment is provided by the preformed tray that is biased to take up the cavity width encountered. Both skins remain independent of each other. Adverse thermal bridging is avoided.
The Type C Cavitray extended ends that project beyond each side of the wall opening shelter whatever reveal closing method is deployed, while also ensuring a naturally-occurring perp is always locatable to accommodate stop ends in the optimum position.
CPD silent study tutorial provides some interesting data; https://www.directcontactexhibitions.com/ select CPD academy, press Cavity Trays 3.
