Cold roof decks, Europeans have been successful at venting the cold roof deck for a long time, How? Permiter edge vent, along with mushroom vents. They have studied it for years and the venting along with very good vapor retarders and installation, and paying close attention to sealing, these techniques stop the condensation, Venting is a must 2" minimum space. (yes cold climate, vented flat roofs, insulation from below or "cold roof") they got (or can get) it to work, why because many times they must use a cold roof technique since they retrofit buildings that are hundreds of years old. (they also screw up, but again it is about the sealing and craftsmanship) The big problem here is that the mechanical system must move down into its own interstitial space.
Cold roof decks, Europeans have been successful at venting the cold roof deck for a long time, How? Permiter edge vent, along with mushroom vents. They have studied it for years and the venting along with very good vapor retarders and installation, and paying close attention to sealing, these techniques stop the condensation, Venting is a must 2" minimum space. (yes cold climate, vented flat roofs, insulation from below or "cold roof") they got (or can get) it to work, why because many times they must use a cold roof technique since they retrofit buildings that are hundreds of years old. (they also screw up, but again it is about the sealing and craftsmanship) The big problem here is that the mechanical system must move down into its own interstitial space.