5 Aug 2014

How good does a Damp Proof Membrane have to be?

A reader asks how to detail a damp proof membrane (DPM) on a solid floor where there is a service penetration. The clever-dick answer is that you should avoid service penetrations through ground floor slabs but, in reality, that's rarely possible. The question is then do you go for the full gas-barrier treatment with proprietary fixtures and fittings like Top Hats, as shown on the Visqueen website, or do you do something more rudimentary with sticky tape and plastic bags? Or maybe even just cut a hole?

Interestingly the building regs guidance (Part C in England) is silent on the matter. Neither do the NHBC's technical standards have anything to say about it. They both indicate that a DPM must be installed and that overlapping sheets should be taped together, but the fiddly issues like corner details and service penetrations are ignored.

What should we make of this? That DPM's don't really matter very much? Or that they matter but that you don't have to go overboard on the detailing? They are not gas barriers and therefore there is no danger should they not work perfectly? I'd be interested to hear how others treat their DPMs.


  1. Don't use em - insulating downstand french drain around the perimeter instead

  2. I think there's a lot to be said for painting on the DPM e.g. synthetic rubber/bituminous sludge like Synthaprufe or similar (as long as you get someone else to do it!) - you can then concentrate extra attention/coats on the most vulnerable bits like around pipework etc..