Basement Waterproofing Membranes - The Difference Between an Insulated Membrane and Insulating One

I have just come away from a meeting with a major supplier of basement waterproofing membranes.  Like most suppliers in the industry they have always supplied the plastic dimpled membrane for cavity drainage, and condensation has always been a potential hazard with such membranes.  The industry has wrestled with this problem for decades, ever since this generic type of waterproofing became prevalent.

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In the 1970's and '80's it was industry standard practice to recommend that the air space between the membrane and the plasterboard lining be ventilated top and bottom so as to prevent condensation.  During the '90s and early part of the 21st century this advice was generally changed to 'don't ventilate the cavity' as it can actually increase condensation on the membrane by bringing a constant stream of humid air into contact with the cold surface of the membrane itself.  So the advice changed but the problem did not go away.

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Whilst the development of good quality and affordable dehumidifiers which are now readily available in most electrical stores has helped, the potential for condensation on a cold plastic surface is still a real risk.  This risk is made worse by insulating in front of the membrane.  'Why?' you may ask, 'surely if i insulate something I will keep it warmer?'  I t was hearing that very same quote today that inspired me to write this article especially as it came from a major supplier of plastic membranes.

I am not a physicist, I don't even know whether it is the first or second law of Thermodynamics and it doesn't really matter which, but i know that energy cannot be created or destroyed - that much is accepted wisdom.  So... If you are going to make something WARMER by putting in an insulation barrier, then you must also be making something else COLDER by the same amount.  insulation does not generate heat.  It does not make anything warm.  It just stops the transfer of heat from one place to another, or at least slows it down.  So if the room is warm and the ground outside is cold and the membrane is on the outside wall and you then put insulation in-between the warm room and the cold wall you make the wall and anything else on it (the membrane) COLDER and at the same time you keep the room WARMER.  And if, by doing this you make a vapour barrier colder then you increase it's risk of condensation.

Now the difference between insulating a membrane as described above and an 'insulated' membrane is that in an insulated membrane the insulation is an integral part of the membrane, not a separate element in front of it, in fact the insulation is actually BEHIND the vapour barrier, i.e. in-between the cold wall and the vapour barrier itself so that the vapour barrier is actually kept warmer rather than colder.  It is as simple as that.  Insulating in front of a membrane and thinking that you are keeping it warmer, is an easy mistake to make I guess but with a little careful thought also an easy one to avoid.

Read more on thermally insulated membranes and waterproofing basements

Basement Waterproofing Membranes - The Difference Between an Insulated Membrane and Insulating One

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