As a damp proofing specialist I regularly use membranes to avoid damp. However, the use of cavity drain membranes is increasing and on many occasions I find that they are incorrectly specified and cause problems.
This is not the fault of the materials, merely poor knowledge of the specifyer. Sometimes a builder, sometimes a customer and even surveyors and architects get this wrong now and again. I see it all over Yorkshire, particulaly in many of the student lets in Leeds.
Anyone can apply a membrane to a wall, but think…what is the purpose of it? Is holding damp back? Holding damp in? Both?
This video, shot in Chapel Allerton, Leeds, is an example of a membrane being used without an appreciation of it’s limitations and the potential for problems, if the membrane is not integrated into a complete system.
What went wrong here?
Well, for starters, the membrane was not used in conjunction with any drainage, so it would not hold back water (which I suspect was the original aim)
No account of the humidity in a below ground kitchen was taken, so water condensed between the membrane and the back of the linings, leading to copious mould growth and an unpleasant smell.
Ventilating the linings only made this worse
The floor was not integrated into the waterproofing system so the skirtings were damp and beginning to rot.
If you are considering using a membrane, think about what it can do, what it can’t do and what any unforeseen consequences of the installation may be. These are normally installed in older properties, with poor insulation, possibly solid walls. The vapour check caused by the new membrane must be taken into account. Causing a draft down the face or reverse of the membrane is not the answer – good control of humidity is.