insulation to new external wall

31 May 2006
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United Kingdom
I am building an extension and and would like to know what thickness wall insulation to put in the cavity.

Normal wall section of 100mm block, cavity and then brick.

I have 65mm cavity on my drawings but with nomal rockwall (65mm)would that give me a good enough u value.cheers
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If the drawings have been passed, the what does the specification say?

Unless you are adding extra insulation inside, then 65mm cavity, and especially 65mm rockwool is inadequate with 100mm blocks.

You are looking at 100mm insulation with rockwool
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Is Rockwall preferred over PIR panels like Celotex? Based on the thickness required and it seems 65mm of rockwool isn´t thick enough to insulate sufficiently, what mm of Celotex / Kingspan / Xtratherm is required?

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