My house is around 150 years old and in one of the ground floor bedrooms, we have strange damp spots on all the walls that are external. Have included a picture to show the worst of it. As you can see it starts near the skirting board but does not fully cover the area then it rises into circular patches. Has anyone seen this before? As I would really like to get the walls repaired. The walls are papered in plain white as they were quite rough then painted over. As you can see the paint in flaking off. Any help is greatly appreciated.
I would guess from the location and distribution of the damp patches that, the rain is coming through the wall, the rain is making the wall cold and water vapour in the room is condensing onto the cold patches. Take a careful look at the wall outside. Is it facing the prevailing wind? Is the rain hitting and spreading over the wall? Is the wall in bad condition with cracks, missing render or pointing?