The old upvc windows are double glazed but not to modern standards. However, even though the energy savings would be good, the cost of replacing them was far too high. What I did though was to have them overhauled. They had not been maintained and the hinges needed oiling or replacing and the rubber strips around had perished in places.
The Velux window in the attic would probably be worth replacing at some stage. It may be possible to just replace the glass, for although it is double glazed, it is not low E glass which would make some difference in this room. As ever, it is a question of cost.
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Windows