With the heavy rain recently I noticed this under the wallpaper. With a section removed the damp is concentrated in a line: Above the window (inside) the top is a wooden lintel. Along this line is a crack (horizontal along) where damp is coming through and has spread up slightly by circa 15cm's. Nothing else around.
Looking at the wall from outside I can't see any damage to the brickwork but directly above the window the pointing looks newer than the rest.
This leads me to think its lacking any of those little plastic drain-fixtures that you fit into the mortar.
If I self-fit drain fixtures (vertically in the mortar - say 2? Above the window frame would this help?
If its a builder-only thing is a fix a big job???
I know the house has had loft insulation and cavity wall at somepoint - I doubt it can be the lack of circulation in the loft- why? The moisture/wetness is concentrated along the line above the window.
Please feel free to correct me! (I'm trying to download pics but can't find my camera cable)
The best guess I can give you is that the outer brickwork was and is now, supported on the window. The brickwork has cracked and been repaired hence the new mortar. When you had ventilated cavities water penetrating the outer brickwork skin evaporated in the cavity before it got inside but the cavity wall insulation has stopped evaporation.
You really need a cavity tray and weep vents to solve this problem.
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