Insulating internal cavity wall

22 Dec 2015
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United Kingdom
I'm building an extension and I'm wondering whether the insulation will work properly for my internal wall. I have a heated room and a garage, but I want the option to convert the garage in the future, so I want it insulated.

I'm using rigid "full fill" insulation, which is 90mm with a 10mm cavity. It's this 10mm cavity that I'm having doubts about. I'm wondering whether the garage will be insulated properly if there is a 10mm gap between the wall and the insulation. This is more of an issue at the end of the wall where it meets the other cavity as there is a gap below the insulation where air/heat could get through.

There are two options I can think of. The first option is to close the cavity with a block and then cavity closer, which should eliminate/reduce the thermal bridging from the side. The other option is using a proper full fill insulation like DriTherm32, but that would result in a much lower U-value (0.22 instead of 0.16).

Does anybody know what is usually done and whether closing the cavity would solve the problem (if it's allowed)?


  • Garage Cavity Detail.png
    Garage Cavity Detail.png
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