Installation of additional insulation for underfloor heating - cables lie on the raw floor slab

Don't know if that can be used, usually [Butylband] is used there.

You have to get into it there, if necessary ask a specialist. Siga manufactures two types, yellow for indoors and green also for outdoors. That is also waterproof. I think the latter works. But otherwise ask or call Siga.

All right. I will contact the specialist dealer again from whom I received a good offer. However, no adhesive tape is included there.

However, he is the only one who has so far suggested a construction foil that I should place under the insulation on the upper floor. From your point of view, is that necessary as a vapor barrier? I would then have to completely seal it with adhesive tape. So I would end up with adhesive tape again, which was not offered.

Actually not necessary, since vapor barriers are only made at the transition from cold to warm. And inside the house it is rather warm/warm than cold/warm.

Do you consider PUR insulation boards (2-3 times more expensive) necessary as insulation for the underfloor heating on the upper floor? This has now been offered to us. Isn't that somewhat oversized? The additional cost is about 200€. I don't think I will make that back, right?

Construction on top:
2 cm multipurpose insulation board EPS 0.35,
3 cm PUR insulation board Therma TF70w.
Construction foil (I think I'll leave that out now)

Is impact sound insulation already ensured by the two boards?
Would it also be possible to lay a single layer of 5 cm multipurpose insulation board on top?

I only know the following. I asked the heating installer to use the good, harder insulation boards because then the screed does not sag later. Hardly more expensive, but the result is that all our silicone joints at the wall-floor connection are still intact after almost three years.