Insulation height?

[Ed209]

The height I have between the wooden ceiling and the underside of the man made slates /breathable roofing membrane is 115mm should i just put 50mm celotex in or could i make it up to 75mm with additional 25mm but this would only leave 40mm air gap.
This is a summer house by the way


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[Ed209]

Just looked and realise that you can get celotex etc. In 75mm


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[skipdiver]

Don't think you need an air gap if you have breathable roofing membrane?

 

[Ed209]

Thank you that makes sense


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