I've just stripped the wallpaper from the bedroom wall. Above the
window is a patch of black mould / mildew.
On closer inspection I found there is an airbrick venting the cavity
above the window. I suspect that driving rain gets blown into the
cavity and has caused the damp.
My thoughts are to put a louvred vent over the airbrick to allow
ventilation, but reduce water ingress.
I can then treat the mould and decorate.
Any other ideas?