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Hi, The general consensus is that 12.5mm thickness is better than 9.5mm for plasterboard because it is sturdier. However, what about when you are using warm board. So 9.5mm plasterboard and 20mm insulation? Does the the 20mm foam help make the 9.5 plasterboard sturdier and less likely to give you hassle? Thanks a million

Thanks for feedback. The warm roof u-value guideline is now 0.18, I think https://www.enviroplyroofing.co.uk/u-value-changes-for-flat-roofing/#:~:text=This type of insulation is,need to increase to 150mm. So if you have150 rigid on top, which is thermal conductivity 0.022 / 0.150 = 0.146 which is well below 0.18. So wondering, is it worth the risk of adding more fibre glass underneath? I don't think it will make much difference and just incurs a risk. Thoughts appreciated.

Hi, We are in the middle of building a flat roof extension. Builder is doing 150mm rigid insulation warm roof insulation In the actual room there are 300mm joists and engineer has advised to make this even better to add 100mm wool or fibre glass. A friend is saying this could cause condensation but I am not sure how Could anyone advise? Thsnks