Cavity Wall Insulation?

29 Aug 2007
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United Kingdom
My house was built circa 1997 so should have cavity wall insulation. I am re-doing my bathroom currently and have reomved a piece of plaster board which form an interior window sill which has exposed the cavity.

I can't really see the insulation in this cavity. About 8 inches from the bottom of the window there is some material but it looks more like rubble. There is a good 8 inches from the top of this material to the window and it extends right along. See the pictures below. It lloks to me that either there is no cavity insulation or it doesn't go all the way to the top. Or is it supposed to be like this?

If not should I fill this void with rockwool / spray foam before closing in?

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Loose fill rockwool or equivalent.
Do NOT use spray foam.

There should be insulation in there, but clearly the builders 'forgot' to put it in.
Isn't that a sheet of insulation fixed to the 'top" half of the wall with a big gouge in it I don't know the standards applicable then, but 50 mm or so of sheet might have been appropriate as it was ( I think ) for my house 10 years earlier.
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Had some on round to inspect the cavity. Apparently it is well know that when our houses were built the certificates were signed to say the cavity walls had been insulated but they weren't! They did a borescope inspection and sure enough the cavities are empty.

Got an ECO subsidy so it is costing £149.

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