Floor structure for ventilation system on the upper floor

Hello,

for our planned single-family house (city villa, 2 floors without a basement), which will be built by a developer, we would like to install a controlled residential ventilation system. The ventilation installer would like to use oval ducts with a diameter of 115x51mm. These ventilation ducts are to be installed in the floor structure of the upper floor, between the concrete slab and the screed. The floor structure currently looks like this:
- 1.0 cm covering
- 6.5 cm cement screed CT-C25-F4 + fibers S65 H45
- 10.0 cm impact sound insulation
- 18.0 cm reinforced concrete slab C20/25

Now the construction manager has "raised concerns" and says the floor structure would have to be raised by 4cm (which would cost +1200 euros).

If I understand correctly, the ventilation ducts (5.1 cm height) would have enough insulation above and below (from the 10.0 cm impact sound insulation). I have shown this in the attached picture. Is there anything fundamentally wrong here?

Thank you for your advice.

He probably has concerns that the screed might give way along the channels when walking on it.

Controlled residential ventilation on raw subfloor ~6cm, with 6cm insulation on top (or more if calculated as such), then 6-7cm screed, and flooring on top.
There are regulations for laying flat ducts to prevent them from buckling (I believe minimum distance 30cm side by side).

We have
25 cm solid wood
9 cm filling
6 cm screed
Floor covering

Accepted by the expert.

Ventilation pipes lie on the wooden ceiling

We have 25 cm solid wood 9 cm loose fill 6 cm screed Floor covering

Approved by the expert.

Ventilation pipes rest on the wooden ceiling

So, in your case the pipes are directly on the ceiling, i.e. on the solid wood without insulation underneath and only with insulation/loose fill above?

Controlled residential ventilation on a raw screed floor ~6cm, on top of that 6cm insulation (or more if calculated that way), on top of that 6-7cm screed, on top of that covering.
There are regulations for laying the flat ducts so that they do not bend (I believe the minimum distance is 30cm side by side)

Hmm, I did not fully understand this setup.
Which regulation must be observed here?
Thank you!