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Actually, it's not in the bathroom at all! It's in the living room which is a 100+ year old cottage with huge thick walls, so there's no cavity walls in that part of the house. It's in the bedrooms (which is a new part). I've been wanting to change the windows for ages 'cos they're just 2 big panes and don't a small opening part. I'm always terrified of the cat falling out so they don't get left open much at all. That may well be the good excuse to get them replaced now. Thank you all again.