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wezza79 · Joined: 22 Dec 2007 Posts: 4 Location: London

We moved into our first floor flat last year, and have some problems with damp under the main bedroom window. It's a large sash window, in reasonable condition, except for the bottom right hand corner of the frame, which is slightly rotten.

A patch of wall just underneath and to the left of the window seems to be suffering from damp. When we moved in there were some pale brown swirly stains on the wall, and it felt cold/clammy to the touch. We recently decorated the room, which has covered those marks - but a patch of lining paper came away from the wall in that spot, which we've since patched up with filler.

The mortgage surveyor who first highlighted the problem said it was due to the rotten window frame/sill and that the frame should be replaced - but we find that a bit odd, given that the area of damp is on the opposite side to the corner of the frame which is rotten. Meanwhile our structural engineer (who we had to call in to check out something else entirely) had a look and said he thought it was caused by condensation.

We've had a look outside, and all the drains that run along that bit of wall seem in good condition, with no evidence of leaking. If we get up very close to the wall under the sill though (on the inside), you can see some tiny holes and feel a draft coming through - does this suggest the bricks are porous in some way?

Any advice or thoughts on what might be causing the problem and how we treat it, gratefully received.

Many thanks.