Work is starting on my flat to pitched roof conversion on a semi third bedroom extension next week, the builder has recommended 150mm thick kingspan to fit in between the existing flat roof rafters which are 150mm deep, seems a bit OTT to me as I have read kingspan is at least twice as efficient as rockwool.[/b]
Kingspan Insulation thickness
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C
cmother1
That's the same as I had to fit on my extension a couple of years ago, but it had to be 100mm between the rafters and 50mm continuous sheet below them. This was to provide an air gap above the insulation (100mm in the case of the timbers we were using).
It depends upon how good the insulation is elsewhere in the property.
Was this a calculation or an educated guess?
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Why would it make a difference how good the insulation is elsewhere in the property, please explain.
He said he'd worked it out and it's better to over insulate than under but @£49 a sheet it's expensive.
Anyone know where it can be bought cheaper
BTW the insulation is not up to spec but I plan to replace it with 75mm between the ceiling rafters and 75mm between the roof rafters, when funds allow.
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