Calling Piglet John and all other kindly knowledgeable people! 3 weeks ago I painted in the living room - 2 days later noticed this band of damp that has appeared just over half way up my living room wall, next to the front bay window frame. It goes back along the wall and round the corner wall too. Under this band there is a semi-circle of damp at the window frame edge. Long drip stains have now appeared in the wallpaper too. Cannot understand it at all as it was not there prior to painting.
Outside the pebbledash and the window seal seem fine to my untrained eye. I have looked at the guttering in pouring rain, doesn't seem to be spilling over. Upstairs radiator not leaking. Victorian semi.
Have had 2 builders round - first suggested checking out the guttering. Second said it was probably condensation and to put in trickle vents (really not sure on that one...) Have another coming on Friday. But am very worried that no one will work out where it is coming from. Ideas welcomed. Thank you. 