Condensation behind insulated plasterboard

13 Jul 2011
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United Kingdom
Hi all

Sorry if this is a bit long winded but I want to describe exactly what I've done so that I can get the best advice. I've then put some questions at the end:

I've renovated a few properties in my time and the usual M.O. in regards the walls is to steam off the old paper and skim. This latest project, however, had a sort of foil and clingfilm backed wallpaper on the external walls that I can only presume was a form of vapour barrier. It was an absolute bugger to get even a small section off, we're talking an hour for a patch the size of an A4 sheet of paper! So I decided that this would be a good time to batten out the walls and add some insulated plasterboard, therefore improving the insulation and negating the need to get the wallpaper off; particularly as this is a Victorian end terrace with solid walls and so a bit nippy in winter.

I used Gyproc Thermaline Plus fixed to 2X1 treated battens and put a piece of DPC behind the battens. The Thermaline is advertised as "the closed cell structure of the foam provides integral vapour control". This is why I used it as I thought it would save me messing around with various different layers.

Before fixing the insulated plasterboard I fixed some new metal boxes to the battens for double sockets, then lined up the boards, pressed them against the wall then turned them back around and I could see the imprint of the box in the foam so I could cut it out. I then fixed the boards and the rooms were then skimmed by my plasterer.

All going well so far, but today (about 2 weeks after plastering), I noticed that there is a fair bit of condensation in the metal boxes.

1) it has dawned on me now that perhaps I have totally buggered the integrity of the vapour barrier by cutting holes for sockets. Thoughts?

2) of course there will be a lot of damp air in the house what with no central heating, 2 guys working 10 hours inside, only 2 weeks since plastering and the fact that it hasn't stopped raining in ages; do you think that when work is finished and the central heating is on then it will get rid of the problem? There is also the fact that there is no skirt and the socket plates aren't fixed yet so the insulated plasterboard will be better sealed when this is done.

3) the problem only really seems to be occurring on one of the external walls, although others have been boarded in exactly the same way. The house is an end of terrace but then another terrace starts less than a meter away (there is a side path between the two). It is this external wall that is suffering from the condensation.

Any advice/criticism greatly received. This may have been an expensive learning curve!

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