Floor construction without screed directly on basement ceiling

We will execute such a floor construction. Depending on how much insulation you need on the floor (possibly specified by the energy consultant depending on the desired goal), this is possible. Apparently, you have a basement underneath, so you could even do without a vapor barrier, but it would probably be safer to lay such a foil. There are systems, for example from Steico and others, called SteicoFloor, where the joist layer is not screwed down but laid almost floating and decoupled because the fiber insulation boards rest on the floor, but the wood beams are a few millimeters above. You can then lay anything on top, such as screwing down floorboards, which is what we will do. If you want or have to install different insulation, I was recommended, in my opinion, a sensible method, namely to lay a layer of Styrofoam immediately after the vapor barrier, as it compensates well for small stones or cement residues. Then lay the joist layer floating on top, i.e., a squared timber with insulation boards in between. Due to the KfW standard, we need a certain insulation class there, so we will probably execute it that way. Instead of Styrofoam, you can just as well use fiberboards. It also depends on the desired insulation result. But you can also screw the joists directly to the floor; however, you should make sure that they are screwed down firmly permanently, as otherwise they might creak individually over the years. You can also decouple the joists with a layer of felt or similar in this case. I had it like this in the old house, and it worked well. Now we will probably do the floating solution as described above. We will also not have a screed; the discussion about that is pointless; for a floorboard floor, you certainly don’t need one and it is rather a hindrance.