Best way to insulate a new 50mm cavity wall

29 Mar 2023
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United Kingdom

We're building up the walls on our old conservatory footing which means I'm stuck with a 50mm cavity.

What is the best way to insulate a 50mm cavity? 25mm celotex on the inner leaf with a 25mm air gap?

We will insulate on the inside too.


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Full fill wool would be cheaper if it's suitable. Do you have a target u value or just whatever is economical?
Thanks for reply.

Building regs don't apply but I want the best performance out of what cavity I've got.

It's not a big space so the difference in cost between options isn't really a factor
If the wall is already there a blown wool fill will work.
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It's currently about 18" but will be built full height with new brick and block work.
Ecotherm EcoCavity full fill PIR is the best insulation value you will get for the cavity. If you want more you will have to line the internal surface with a thermal laminate instead of standard wall board.

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