Open wooden beam ceiling on the ground floor - insulation construction on the upper floor beneath the screed?

Hello,

next week we want to carry out the work for the screed installer on the upper floor.

We have a wooden beam ceiling with Siljan planking (from below exposed visible beams with visible formwork), and a total floor structure of 19-20 cm should be realized on top, since many installation lines run there, such as from the ventilation system (6 cm pipes).

We were recommended: a total of 12 cm rigid foam insulation EPS DEO100 035 in 2 layers, e.g. 6+6 or 8+4 cm, filling cavities at the pipe routes with loose fill. On top of that a construction foil, to which the heating installer staples the pipes of the underfloor heating (hot water), and then 6-6.5 cm screed + tiles/laminate. And of course a PE edge insulation strip. The screed will be a cement screed (earth-moist).

Now the question: only DEO100 insulation and no impact sound insulation (DES)? If yes, how thick should the impact sound insulation be?
And the other question: we are getting a freestanding bathtub type Paris that stands on 4 feet; should a thicker insulation be laid underneath? It was said that impact sound insulation might flatten and the screed could crack as a result...

Regards

oh yes, a mineral wool board from Rockwool is also available as a choice for [Trittschall]

...... and then comes 6-6.5 cm screed + tiles/laminate....

The floor covering plays a significant role with regard to the design of the heating surfaces (flow temperature, mass flow, installation spacing, heating circuit length, number of heating circuits, pipe diameter, etc.). In terms of overall efficiency or costs by no means a minor issue!

..... It was said that an impact sound insulation would probably compress and the screed could crack as a result...

Who says that? What does the compressive strength of the screed have to do with the static effect of the impact sound insulation?