I recently took down the ceiling in my small back bedroom. Before putting up the new plasterboard I put celotex (like kingspan) insulation boards between the joists. Where the roof slopes down near the eaves there is only a 2 inch gap between the top of the joist and the roof underfelt, so at these points, approaching the eaves, there is similarly only this 2 inch gap between the celotex and the underfelt.
Now, having had the ceiling plastered and the walls reskimmed and having emulsioned it all I’ve found a brown stain at the bottom corner of the ceiling, near the eaves. Since the roof is very sound, I believe that I’ve got some condensation forming there, possibly because where I’ve jammed the celotex in I may not have maintained the full 2 inch gap to provide air flow. Obviously it’s impossible to rectify this without taking down the ceiling! So what I was wondering is: could the condensation problem be solved by putting in some sort of roof vents, to increase the air flow above the insulation and joists. My roof is made up of pantiles. Thanks.
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