AdaminCymru Posted May 9 Share Posted May 9 Hello I have plans for a cold roof on a loft extension. I believe cold roofs can be problematic with heat retention in warmer months. The rafters that are currently spec’d are 200x47mm and total cold roof thickness 342mm. I am wondering whether a warm roof could be a better option, but I do not want to compromise on head space. If my engineer agrees to say a 125x75mm rafter instead of 200x47mm, what is the minimum thickness warm roof we could achieve here? any input greatly appreciated Link to comment Share on other sites More sharing options...
Dave Jones Posted May 10 Share Posted May 10 you wont have the headroom, it need above your ceiling/wiring. osb deck, vapour barrier, celotex, osb, rubber/felt etc. 200mm needed min really. then below that your 6x2 truss, plasterboard etc etc Link to comment Share on other sites More sharing options...
DevilDamo Posted May 10 Share Posted May 10 Normally, you’d require 150mm on top. Link to comment Share on other sites More sharing options...
EdHat Posted May 24 Share Posted May 24 You'll need 140mm or 150mm depending weather it's refurbishment of an existing element or a new thermal element. When I've needed to keep the height down I've been able to reduce the 140mm down to 90mm by using a multi-foil insulation over the joists first. You could also look at Recticel Deck VQ which has a lambda of 0.008 and I believe you can meet the regs with 90mm but I expect it is expensive. Link to comment Share on other sites More sharing options...
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