Our house has a side extension over the integral garage.
There is a 'legacy' cavity wall between the original house and the garage and the extension rooms over the top of this garage.
This cavity wall has never been filled (i.e. the whole original air gap is present) except where cavity wall insulation has 'leaked round' for about half a metre of cavity at each end where it meets the perimeter walls.
At the top this entire cavity is open into the loft space.
It seems to me that a cavity wall that essentially opens out into air which is effectively as cold as the air outside, is not a very effective cavity wall! (but then again I'm not a builder so what do I know!)
I've read elsewhere about using blanket insulation (ideally the stuff with foil surround - space blanket) to seal the top of the cavity by ramming it in.
I) Is this a good idea? ii) Where in the approved building regulations documents is sealing the top of wall cavities talked about?
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