Vapor barrier attic, insulation Styrofoam EPS 035 Deo, concrete ceiling

Hello everyone,

I am new here and have a question right away.

I am currently planning to insulate the top floor ceiling in our house. I have already been to several building material suppliers, but I received different information regarding the vapor barrier. The ceiling is about 25cm thick and made of concrete/screed. Styrofoam (EPS 035 Deo/honeycomb with step joint) is to be used for insulation. Parts of the area are to be later covered with OSB boards for walkways. Now I am not sure whether a vapor retarder is needed or not. I have attached 2 photos from the attic.

Regards, Marcel

Hello,

...Now I am not sure whether the vapor barrier is needed or not.

A vapor barrier is always on the "warm" side, here therefore below the insulation layer. The insulation of the knee wall is incorrect and also largely useless.

Best regards

Your reinforced concrete ceiling is already a great vapor retarder. But it is not a vapor barrier. It therefore depends on what comes "from below" – wet rooms? And how the minimal moisture on the vapor diffusion side above can possibly "escape." If a vapor barrier is omitted, a diffusion-open construction in the insulation layer is required. Here, I would, quite layman-like, point out EPS and OSB boards as the least suitable building materials... But there are also EPS boards with a chipboard glued on top. However, you should have this calculated specifically by a professional. Insulating the attic/the top floor ceiling is not trivial and there is a lot that can go wrong.

Hello,

below are living spaces with internal bathrooms. I was offered the following membrane: vapor barrier film blue B2 200my. The film must then be glued seamlessly to the knee wall and the ridge walls? Or? So do I need a vapor barrier or a vapor retarder? The attic is not supposed to be fully covered with OSB boards, but only the walkways. Of course, I can also use chipboard here. Covering the entire attic with Komi boards makes no sense because the attic is not used, and you only need access for maintenance work on the chimney, satellite system, etc. Possibly for storing balcony furniture in winter.