Currently at structural engineering stage for building regs submission and looking at roof covering loading. The choice of waterproofing is subjective and well documented; single ply, bituminous, EDPM, GRP - seems that everyone has a preference or horror story. Anyway more fundamentally my design is showing a cold roof design for a new build flat roof extension (parapet roof), however having researched flat roofs the majority of advice is to go for a warm roof to eliminate interstitial condensation (eg Bauder, NFRC) . As I chose the timber frame provider to avoid this issue at the sole plate I'm thinking that I'm walking into this problem up above.
Any experience or thoughts welcome.