Here is the problem: Warm moist air migrates to the cold wall surface and forms a mouldy appearance. Your option is to dry line the exterior walls by using a Kingspan product, get technical advice from them. You will now find that the warm moist air will settle more on the next coldest surface, ie the windows. Each morning you may dry off the windows with an absorbent cloth. Get yourself a dehumidifier, and use it each day in cold weather, it will collect a lot of the moisture from the atmosphere and help to allay the problem. Please note that even double glazing still does not prevent the moisture from forming, but at least it is easy to dry the window(s) every morning, less than 5 minutes work. There is now a vent available which helps to air the room without subjecting the occupants to a very uncomfortable draught, a bit pricey but anything worthwhile is worth it. There should be a regular heat source used in the room, perhaps not all the time but when occupied at least. The worst room in the house for producing condensation will usually be the bedroom;it is incredible the amount of moist warm air produced by , say 2 persoms sleeping in a bedroom, you will see evidence of this every morning. This happens even if you have the window open.