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Damp Floor in Outhouse Possibly Caused by Insulation not Letting Wall Breath

Posted: Wed Nov 22, 2017 1:12 pm
by Crashland
Hello.
I own a mid terrace house with an adjoining outhouse which I wished to convert to a cloakroom/utility room. The outhouse was originally divided into a toilet, a presumed coal house and a small utility area.
I removed the old toilet and cistern and knocked down the dividing wall between the toilet and coal house and have reinstalled a new close coupled toilet. The dividing wall had a dpc but I can't see a dpc in the outer wall.
Anyway, the toilet had wooden cladding on the walls which I removed, which was damp and rotten in places. In an attempt to make the area less uninviting I battened the walls and roof area and installed polystyrene sheet insulation with the intention of cladding the walls and ceiling with uPVC cladding panels. However, with the recent rains, I have found the concrete floor is now very damp, particularly along the external wall.
Is this caused by the insulation preventing the wall from breathing? If so, what is the best way of moving forward with the project?
Thanks.