| I have just come away from a meeting with a major | | | | the first or second law of Thermodynamics and it |
| supplier of basement waterproofing membranes. Like | | | | doesn't really matter which, but i know that energy |
| most suppliers in the industry they have always | | | | cannot be created or destroyed - that much is |
| supplied the plastic dimpled membrane for cavity | | | | accepted wisdom. So... If you are going to make |
| drainage, and condensation has always been a | | | | something WARMER by putting in an insulation |
| potential hazard with such membranes. The industry | | | | barrier, then you must also be making something else |
| has wrestled with this problem for decades, ever | | | | COLDER by the same amount. insulation does not |
| since this generic type of waterproofing became | | | | generate heat. It does not make anything warm. It |
| prevalent. | | | | just stops the transfer of heat from one place to |
| In the 1970's and '80's it was industry standard | | | | another, or at least slows it down. So if the room is |
| practice to recommend that the air space between | | | | warm and the ground outside is cold and the |
| the membrane and the plasterboard lining be | | | | membrane is on the outside wall and you then put |
| ventilated top and bottom so as to prevent | | | | insulation in-between the warm room and the cold |
| condensation. During the '90s and early part of the | | | | wall you make the wall and anything else on it (the |
| 21st century this advice was generally changed to | | | | membrane) COLDER and at the same time you keep |
| 'don't ventilate the cavity' as it can actually increase | | | | the room WARMER. And if, by doing this you make a |
| condensation on the membrane by bringing a | | | | vapour barrier colder then you increase it's risk of |
| constant stream of humid air into contact with the | | | | condensation. |
| cold surface of the membrane itself. So the advice | | | | Now the difference between insulating a membrane |
| changed but the problem did not go away. | | | | as described above and an 'insulated' membrane is |
| Whilst the development of good quality and | | | | that in an insulated membrane the insulation is an |
| affordable dehumidifiers which are now readily | | | | integral part of the membrane, not a separate |
| available in most electrical stores has helped, the | | | | element in front of it, in fact the insulation is actually |
| potential for condensation on a cold plastic surface is | | | | BEHIND the vapour barrier, i.e. in-between the cold |
| still a real risk. This risk is made worse by insulating in | | | | wall and the vapour barrier itself so that the vapour |
| front of the membrane. 'Why?' you may ask, 'surely | | | | barrier is actually kept warmer rather than colder. It is |
| if i insulate something I will keep it warmer?' I t was | | | | as simple as that. Insulating in front of a membrane |
| hearing that very same quote today that inspired me | | | | and thinking that you are keeping it warmer, is an |
| to write this article especially as it came from a | | | | easy mistake to make I guess but with a little careful |
| major supplier of plastic membranes. | | | | thought also an easy one to avoid. |
| I am not a physicist, I don't even know whether it is | | | | |