Is a moisture barrier necessary under floating cork?

Hello, we are having floating cork installed. It is a new building, the screed has passed the CM test, so it is sufficiently dry for installation. Contrary to the manufacturer's instructions, the floor installer does not use a PE foil as a vapor barrier. We find this a bit strange, especially since the installation instructions state that a vapor barrier is always necessary on mineral floors such as screeds. The floor installer says that this is not necessary in new buildings, rather in old buildings and non-basement buildings, although screeds in new buildings generally contain more residual moisture. How critical do you see this, and should one insist on adhering to the installation instructions here?

How critical do you see this, and should one insist on compliance with the installation instructions here?

Is the screed dry or not? What is the foil supposed to protect against then? If it is not dry, you are not allowed to lay any floor at all.

New buildings where the screed tends to contain even more residual moisture.

So you are not allowed to lay floors in new buildings, because otherwise everything underneath will mold? That is what the CM measurement is for. Then you know whether it is ready for installation or not.

Then ask him if he will assume liability if he works contrary to the installation instructions.
VOB DIN 18365 „Bodenbelagsarbeiten“

Is the screed dry or not? What is the foil supposed to protect against then? If it is not dry, you are not allowed to lay any flooring at all.

So you are not allowed to lay floors in new buildings because otherwise everything underneath would mold? That’s what the CM measurement is for. Then you know whether it is ready to be laid or not.

The floor should indeed be dry, but to my understanding, screed always still has residual moisture for ages. Whether this is really relevant is what I am currently trying to clarify here in the forum. Quote from the installation instructions:
"Vapor barrier For all mineral subfloors, such as screeds or stone tiles, a vapor barrier is required. This also applies to concrete floors with integrated moisture barriers or underfloor heating or concrete intermediate ceilings. There must be no partial cold or warm surfaces, as this leads to stresses. Use a plastic film (PE foil) with a thickness of at least 0.2 mm, which overlaps by at least 20 cm at the seams and is glued. Lay the foil so that it stands at least 5 cm up on the walls."

Then ask him if he assumes liability when he acts contrary to the installation instructions.
VOB DIN 18365 "Floor covering works"

Yes, he assumes it. And yes, I know the DIN as well and am considering insisting on compliance with VOB/C as contractually agreed. But I don’t want to cause trouble. Hence the question here in the forum whether this foil is already very advisable. Quote from DIN 18365:

"3.5 Laminate elements laid floating Laminate elements are laid floating; they must be connected with adhesive in the groove on the long and head sides if they do not have a mechanical locking system. The subfloor, except for wooden substructures, must be covered loosely with a PE foil at least 0.2 mm thick, overlapped."

The floor should be dry, but a screed always has residual moisture for a long time according to my understanding.

Yes and? If the floor is ready for installation, it is ready for installation. Think about what you are doing with the foil. The moisture you are alleging will cause long-lasting mold under the foil;-) Install the floor and that's it. Especially if he also takes over the warranty. I can fully understand his statements.

The DIN standards are not developed by expert committees (professionals!) for nothing and are continuously but slowly adapted to current conditions. If a PE foil is prescribed, it may have more purposes than the one you assumed. A floating floor as you described, in my opinion, cannot slide well on pure screed and could therefore warp accordingly. Also consider why many buildings install a bitumen sheet on the screed on the ground floor despite waterproof concrete... But for such questions, we have a mod and floor expert here! (KlaRa) Just contact them...