That would interest me too. We are currently planning our roof structure in the Kfw55 house. Our energy consultant suggested 22 cm rafters with insulation between the rafters + 6 cm wood fiber insulation above the rafters. He says there is NO foil between the wood fiber boards and the roof tiles... The wood boards are both the sealing layer and at the same time vapor permeable. hmm...??? You have a foil... maybe that’s the reason? What procedure is correct now? Foil yes/no?