Hello questioner.
Regarding the PE foil under floating floors made of wood, cork or wood-based materials, the following:
The PE foil is always required.
In new buildings (new screeds), usually only one single residual moisture measurement is carried out. For, say, 120m² this is considered sufficient, but still little when you relate the total area to the 100cm² that the testing authority requires.
There always remains a certain residual risk (accepted by the state of the art) regarding possible multi-thicknesses of the screed or measurement errors (due to the measuring inaccuracy of the CM device).
Also in old buildings a PE foil is necessary because you cannot be 100% sure that the cement screed (this applies only to this) is sufficiently dry. This is simply because cement screeds absorb moisture depending on the room air (here: > 70%), so they can become damp again.
And thirdly, as already noted in one of the posts, a PE foil also acts as a sliding layer. Floating floor coverings always move. Whether thermally induced or by the absorption of (air) moisture!
If you hinder the expansion behavior of the floor covering, the covering surface may soon look like these two attached pictures.
Here too, a covering with cork backing was applied to the actually still unlevelled screed.
My notes regarding the necessary remediation (remove covering, lay PE foil double and lay covering again) were ignored by the executing company. Soon it will become apparent what will happen when operating the underfloor heating. However, I already know ....
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Short answer to your question: Yes, install PE foil approx. 0.15mm single layer!
Regards: KlaRa
