hi this condensation prob in loft, just riped the kingspan off i only got 30 mm air gap dont think this is enough ? shall i increase it to 70 mm and see how it goes ?
I'm not sure about that. if the kingspan forms a good barrier then warm damp air should not be getting behind it, so you just need to ventilate the cold space well. I don't see that the size of the gap is the cause of your problem.
however, if the kingspan does not form a complete barrier, then you need to add some other material to keep the warm moist air away from the cold side, and ventilate the cold side.
the vapour barrier should be on the warm side of the insulation.
cheers thanks 4 that. i think i will add polythene sheet between the t and g and the kingspan, the kingspan is a good fit between the rafters but warm air could be getting through(a few small gaps where i cut them and butt up to each other)
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