I'm decorating the bedroom at the moment and have noticed that the wall with the window is damp. The lining paper has come away round the window and there are a few small mould patches near the bottom of the wall.

When we first moved the previous owners had some sort of polystyrene stuff on the walls and had then papered over this.

So, does anyone have any suggestions on some treatment on how to stop the dampness and what was the polystyrene all about ? Would it be a good idea to put this back ? oh and whats thepoly stuff called so I can price it up !

Cheers