Vapor barrier on screed in the attic?

Hello,

the attic in our house is going to be converted. We have a cement screed that has now been exposed for three years. Floorboards are to be laid (not glued).

Do we absolutely need a vapor barrier here? Or can we start directly with the impact sound insulation?

Hello questioner.
If the floorboards are to be laid (screwed/nail) on a battens, only sufficient edge clearance for ventilation needs to be observed.
If the floorboards are to be laid on a (previously, of course, leveled with filler compound) screed surface, or if there is a bathroom below the attic, a vapor barrier (PE foil, at least 0.15 mm thick and overlapping at the sheet edges and pulled up at the sides to the top edge of the floor) must definitely be used.
Good luck: KlaRa

Hello and thank you.

Does it make a difference if the floorboards are stapled, thus not fully connected to the substrate? I am using 3 mm thick corrugated cardboard as impact sound insulation, then the floorboards on top. There is a bathroom on the floor below, but directly above it in the floor plan, another bathroom is to be created.

You write: "in unserem Haus soll das DG ausgebaut werden." Then continue: "... aber im Grundriss genau darüber soll ein weiteres Bad entstehen." Here one inevitably encounters a problem of understanding, because if the attic is to be developed, no additional bathroom can be created above it (the roof surface is located there). Furthermore, for the absorption of moisture from a screed, it is irrelevant how the parquet elements are later held together. Once again: When laying the parquet elements directly (without battens) on a screed, a vapor barrier must be taken into account! Regards: KlaRa

No, he means that in the attic there is a bathroom planned in the spot where the bathroom already is in the floor below. The question is, is parquet flooring planned there (in the attic) despite the bathroom? On the other hand: Since a waterproofing layer is required in the bathroom anyway, he can probably save himself an additional vapor barrier?

So there is already a bathroom on the upper floor. Projected onto the attic above, there will also be a bathroom in the same place later. Currently, only the walls have been constructed with drywall upstairs; the attic bathroom will be installed after the floorboards are laid. For now, the bare screed remains there.

Everything else is to become a room (studio) that is to be covered now. OK, so a vapor barrier must be placed over the dried screed, then the impact sound insulation, and finally the floorboards.