Should I insulate cavity in bay?

14 Jan 2005
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United Kingdom
Hi, We have a 1930's house with semi-circular bay windows. The outside being tiled. We're having the Windows & window sills replaced, so it would be an ideal time to add insulation into the cavity if it were a sensible thing to do. There is quite a gap and we could easily put the rolled insulation down it. I know that houses are supposed to breathe and am bit worried by insulating the gap we could end up creating damp /condensation where currently, none exists.
Any advice?
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I would urge caution. Bay windows are notorious for letting in water. I would be reluctant to bridge the gap and so allow penetrating damp or leaks around the window to find a route to the inside wall. But maybe I'm being over cautious!
That's kind of what I was thinking. Someone suggested using a Kingspan type of insulation with a membrane on the outside. Perhaps we could put that down the gap towards the internal side, leaving a smaller cavity towards the external side?
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