I will post the link to the author of the drawing below when I find out who it was as this is a very good diagram.

This viewer sent me photos of his sweating cold flat roof that hadn't been build incorrectly and was now sweating so much that water was dripping through into the room below. He hadn't fitted ventilation to between the joists and he hadn't added an AVCL (air vapour control layer)  he had cut lights into the ceiling and air was pouring into the cavity. Mould on the timbers and on the back of the roof decking was starting to grow. So the question is "Can I save my sweating cold flat roof" Using information from some ware on the internet I took some research that shows that plasterboard has a good vaper resistance and the fact that the ceiling is airtight should solve the problem. airtightness in flat roofs is always the biggest problem I come across. People get all hung up about the vapour control layer and forget that more moisture gets into the roof through the movement of air than through a vapour barrier.
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Steven Dickinson
London flat roofing
07802300099
[email protected]

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