January 28, 20215 yr Hi All, My building reg drawings for a new self build, show a pitch roof being insulated with 90mm Kingspan between rafters and 40mm Kingspan with plasterboard to achieve a U-Value of .18w/m2k My plasterer has specified 100mm Xtratherm between rafters and 50mm Xtratherm with plasterboard Would anyone be able to answer my questions? Will I achieve the same U-value? Could there be an issue between the rafters with the xtra depth? I have also noted that 32.5mm Kooltherm 118 is specced around a roof lantern but the plasterer has specced Gyproc thermaline 30mm basic. Any thoughts on this? Thank you Edited January 28, 20215 yr by DerbyLad
January 28, 20215 yr based on the Kooltherm having a conductivity of 0.020 W/mK, that construction is indicated to give you a U-value of 0.18 https://www.uvalue-calculator.co.uk/calculator/pitched roof/insulation between and under rafters (partially filled)/ventilated/no sarking board/150mm/400mm/52.5/90/ Xtratherm has a thermal conductivity: 0.022W/mK, so it should actually be better due to the thickness and give you a U-value of 0.15 (according to the above calculator). You should probably give the Xtratherm technical team on 0371 222 1055 to confirm the u-value. The only thing that i would caution is that with the 100mm between the rafters there is still a ventilation space of 50mm above the insulation (if its a ventilated roof design).
January 28, 20215 yr Author 8 minutes ago, Moonshine said: based on the Kooltherm having a conductivity of 0.020 W/mK, that construction is indicated to give you a U-value of 0.18 https://www.uvalue-calculator.co.uk/calculator/pitched roof/insulation between and under rafters (partially filled)/ventilated/no sarking board/150mm/400mm/52.5/90/ Xtratherm has a thermal conductivity: 0.022W/mK, so it should actually be better due to the thickness and give you a U-value of 0.15 (according to the above calculator). You should probably give the Xtratherm technical team on 0371 222 1055 to confirm the u-value. The only thing that i would caution is that with the 100mm between the rafters there is still a ventilation space of 50mm above the insulation (if its a ventilated roof design). Hi Moonshine, The building spec shows 25mm minimum gap. I've attached a screen shot for you to see Edited January 28, 20215 yr by DerbyLad
January 28, 20215 yr 24 minutes ago, DerbyLad said: The building spec shows 25mm minimum gap. I can't say that i am an expert at roof design but if that is what the architect has specified, go to that. The question is, with the 100mm insulation can you still have the 25mm gap? how big are the rafters?
January 28, 20215 yr 45 minutes ago, Moonshine said: Xtratherm has a thermal conductivity: 0.022W/mK, so it should actually be better due to the thickness and give you a U-value of 0.15 (according to the above calculator). Correcting this is wrong!!!! the calculation of 0.15 is based on 0.020 W/mK, though from my quick calcs 100mm of Xtratherm (thermal conductivity: 0.022W/mK) and 50mm below should give a U-value of 0.18. However i would get confirmation from Xtratherm
Create an account or sign in to comment