Converting garage - dealing with damp

26 Apr 2011
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United Kingdom

I know there are many posts on garage conversions but I have searched the forum and cannot see any prior answer to my question.

I am converting a garage, built in 1962, into a bedroom. It already had an office built in half of it in 2009. It has never smelt damp there at all. However upon demolishing the office and taking up the laminate floor (laid directly on the concrete) there was a very strong damp smell. Subsequent moister traps have revealed that there is damp there on that half of the garage ( not really bad, but definitely there)...but not the half that has always been exposed concrete.

I decided that a raised timber floor would be the best way to go, but I am unsure on how to protect from damp. I had planned to place a vapour barrier ontop of the joists, thinking that if I ventilate the void between the concrete floor and the wooden floor, any damp that does come up through the concrete will evaporate. But reading so many posts about insulating that void has made me think again. A vapour barrier laid directly on the concrete floor, then insulation then the raised wooden floor seems OK...but wouldn't that just encourage and moisture to spread out to the walls? The garage was an add-on to the Victorian house so one wall is the house external wall, the other is two bricks thick but solid, no cavity... the walls show no sign of any damp, but cant see a DPC on the 1962 brick wall. I plan to use plasterboard with the foil backing on the walls attached via timber stud framework.

The garage has two radiators in it already and was really warm in winter, so insulating the floor wasn't ever in my mind.... I guess too much reading various forum posts has instilled doubt ((

Anyone having faced this problem before?
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