We've started to get a couple of damp spots around the house. 2 on the bedroom ceiling, 1 small one in the bathroom ceiling and now I've noticed 2 small patches in the recently painted dining room on the external wall. (which is a small extension). I've checked in the loft and the ceilings are bone dry where the stains are. There is no ventilation in this house what so ever, I've been leaving windows on half lock thinking that would be enough. Obviously not. Would you say this is the main cause of the staining? If so I thought I'd just just drill some 100mm holes, use some 100mm pipe and stick a vent on externally and internally.Will that fix it or have I got other problems?