Window reveal condensation

18 Oct 2016
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United Kingdom
Hi All I have had condensation in a back bedroom window causing black mould.
I have cavity wall insulation, but the horizontal window reveal is always wet after central heating etc.
So the black mould has been removed, I have cut back the wall paper and used Zinsser perma white anti fungal paint.
I have put window vents to reduce the condensation build up, but I still get the same problem.
The upper window reveal has no brick above it, it is the same level as the Uvpc soffit so there is no insulation above the reveal itself and the exterior sealant is sound.
Can I use on the interior 6mm Xps insulation board and bond it in place with a adhesive, if so can this Xps board be plastered over as I will most probably use the Xps board on both vertical reveals as well. firstly i will remove the uvpc strip and use expanding foam to fill in any gaps then replace the strip.
I was tempted on removing the the top horizontal reveal and buying some insulated plasterboard to replace it, but its all hollow behind the reveal itself and I would not know where to fix the board to with it sitting inside the window frame and the reveal is 2.5 meters long and could turn out to be nightmare.
Or is there a better way that this can be done.

Thank you


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