Is bitumen on gable end causing this moisture?
I do not think the bitumen is causing “sweat” its possible that there is a lack of ventilation in the cavity these can be inserted in the walls of each room internally at very little cost.I would also make sure the chimney is vented if not in use,and check if its been capped,just look up from outside,whilst at it make sure no slates are missing.G Luck
