Condensation on Insulation

17 Jun 2015
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United Kingdom

I have a lean to roof on the new extension with a vaulted ceiling. Breathable membrane beneath the tiles. 100mm insulation between the rafters leaving a 50 mm gap between the membrane and the top of the insulation.

The whole surface area of the ceiling has been covered with 40mm insulation (As instructed by Building Control) Then the plasterboard.

Where the plasterboard is yet to be fitted I noticed that there is a thin layer of condensation on the 40mm insulation and the old exterior wall is damp near the ceiling. I was working in there yesterday and everything was dry.

Is this simply the early morning sun has heated up the roof and the room beneath was cold? Or is there a problem with something?

Thank for your advice.
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if its foilbacked insulation with taped joits this will act as the vapour barrier
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