My wife and I bought a house with a new but unfinished dormer.
Normally, I know that dormers are closed with OSB boards, or lie flat on rafters. But in the case of our dormer, the external cladding consists only of plastic facade profiles. Then follows a foil and rolled lead. Between the rafters of the dormer is about 6 cm insulation wool provisionally squeezed.
However, what surprises me greatly is that the dormer is completely open at the bottom. When I remove the insulation wool, I look at the roof tiles with poor insulation from the 60s. I can even look outside under the rolled lead. (The roof stays as is for now, though).
If the dormer were covered with OSB boards and "sealed" flat with the rafter, I would know what to do. Short and sweet:
New insulation wool, then vapor retarder, for example Isover Klimamembran and then Fermacell, since it is a bathroom.
But what needs to be done here now? The previous owner or the carpenter had only provisionally put insulation wool between the rafters here and then the project was abandoned.
Should I close the spaces between the rafters with cut OSB boards, fill the crack with construction foam and then continue with the insulation, vapor barrier and Fermacell?