Damp under Bay window

15 Jan 2007
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United Kingdom

I have a 90 year old house which has masonry window cills and wooden frames. On the interior wall under the front bay window (ground floor)we have an area of damp running along the front and one side of the bay, the damp stretches down from the window cill and varies in depth up to about 9 inches in one place.

I know the obvious thing to check would be for cracks/gaps around the joint of the frame to the cill but I have done this a number of times and to be honest cannot see where the water is entering. This window cill is painted with exterior masonry paint, but is it possible that the stone cill itself may be porous? if so how can I cure the problem?. Does anyone have any other suggestions as to what may be causing this please?

Any help gratefully received, thanks
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could be condensation running off the window running along the sill and finnishing up on the wall

can also be caused /agrivated by bad air circulation
is there any furniture or even a curtain covering the area!!!!
Don't think so, it happens even when there is no condensation on the windows themselves, and only seem to appear after rain so I have convinced myself that it is penetrating damp.
Leaking gutter? If it leaks onto the wall and onto the ground below it can cause probs.
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Another point to mention is what type of windows are they? Wood? could the wood be rotten? I had this problem pushed a nail into the window frame and it was very soft so hacked it all out and replaced the wood that was damaged and it stopped the damp, before i checked the window frame i was in the same position as you and the frame looked ok but it was rotten right through and only the visible bits were ok
Bay walls that age are usually very thin it could be penetrating damp or condensation. thicker insulation and a vapour barrier covered with plasterboard should cure it.
Thanks for all the suggestions, plenty there for me to try. Will let you know what I find
It sounds like a plain old leak to me, you'll just have to find it.

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