-
Yeah I would say the room is normally 70% and up.
On the wall it goes away in summer, but even during the 40 degree heatwave and no rain for 2 months there was a small (5mm) tide line around the window.
If it is condensation we need to increase ventilation but also keep the house warmer (insulation) so air can hold more water?
apc-
Yeah I would say the room is normally 70% and up.
Yeah that's fairly high.
If it is condensation we need to increase ventilation
Yeah. If you have trickle vents make sure they are open and clean them out if they are blocked with gunk. Is the room near a bathroom by chance? If you keep the room at about 18 deg + you'd expect it to be hard enough for condensation like that to form on the surface of the paint, but it might be water in the brick or plaster itself condensating then pushing outwards through the paint.
Howard
Does that room have any ventilation?
Is the humidity unusually high (~70% up)?
I wondered if the brickwork is getting damp somehow - crack in the render or borked seal between window and mortar - and it’s getting trapped behind the render but then it would fuck the plaster and it doesn’t seem to have done that.