Or well, a wet patch about the size of an A3 piece of paper. It's next to and up against an external wall on the carpet, the wall seems dry though. The house is about 300 years old and we have lived here for just coming up to one year. When we moved in we had some damp treated but not that wall. Could it be damp/ground water coming up? What else could it be and what should we do about it? We have no money for expensive treatments.