What is an acceptable DPC for cavity trays in cavity wall construction? NHBC Technical Guidance 6.1/38

Using the right grade of DPC for cavity trays is important in order achieve the NHBC Buildmark warranty.

On 11th November, the NHBC published technical guidance note to clarify what was already in the standards.

Here’s a brief summary of the guidance note and help on selecting the right product:

What DPC can’t I use as a cavity tray?

Polyethylene DPC made to BS 6515: 1984 (categorised as low-density polyethylene). This IS suitable for use as a DPC to prevent moisture rising from the ground but NOT as a cavity tray.

What DPC can I use as cavity tray?

The product selected must meet ALL of the following criteria:

  • Material: Flexible (plastic or rubber) DPC
  • Designed: To prevent the downward passage of water or moisture through the tray
  • Performance: Meets the requirements of BS EN 14909
  • Certification: Third-party certification that confirms their suitability for use as a cavity tray
  • That sounds expensive!

    A high performance DPC can cost up to four times the price of a standard DPC. When comparing quotes, it’s useful to bear this in mind to ensure you’re receiving the right product for the application.

    When does this guidance come into force?

    Whilst this has been part of NHBC guidance for some time (Standards clause 6.1.17), on “all plots starting or at DPC level as at 1st January 2023, the use of appropriate flexible DPCs (as described above) will be required and use of low-density polyethylene DPC conforming only to BS 6515 will no longer be accepted.”

    What’s the right product to select from Multifix?

    We stock the Visqueen Zedex CPT high performance damp proof course as 20m length rolls in widths 100mm, 450mm & 600mm. We also carry a range of Brickwork sundries including pre-formed cavity trays for corners and ridges

    If you already have a Multifix account, roll your mouse over any of the product sizes or references above to see your rates.

    How can I be sure this is the right product?

    The products meet the requirements of BS EN 14909 and Visqueen carry third party accreditation specifying its use as a cavity tray, as per the NHBC technical guidance. Download BBA 94/3059 and their DoP here

    How do I open a Multifix account?

    Click here to open an account.

    Where can I find the full technical guidance note?

    Technical guidance notes can be found on the NHBC website. Here’s a link to note 6.1/38