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

Hello,

We have reached the insulation for the underfloor heating. It was agreed that we would lay the insulation ourselves. However, the installer now says that it was agreed that we would also procure the material.

Now my questions:
What material do I need, or what do you recommend? Our floor structure is 18 to 19 cm at the bottom and 12 to 13 cm in the upper floor.
Does the insulation need to be double-layered at the bottom?
What do you think of Gefitas 300 as a moisture barrier? The problem is that the electrician has already pulled cables over the floor. How should we proceed? Just lay the foil over it?

Moisture barrier absolutely underneath. Loosen cables and place self-adhesive foil underneath. I would find a bituminous membrane too risky, as it could damage the laid cables.

Regards

Is the house basemented? If not, the bitumen waterproofing membrane on the base slab as a moisture barrier is missing. Then the cables, then the insulation material, then the heating pipes and finally the screed decoupled and floating with edge strips made of foam. Please clarify!

No, we don’t have a basement. A moisture barrier is still to be installed. The electrician tells me that I can/should simply lay the moisture barrier over the cables. Are there any pros and cons to this? I am then supposed to place the insulation against the cables and put loose-fill insulation over the cables and water pipes themselves.

No, we don't have a basement. A moisture barrier is still to be installed. The electrician tells me that I can/should simply lay the moisture barrier over the cables.

That is rather unconventional and of course it would be ten times smarter to put it under the cables.... Over the cables it will never, ever be watertight.

Yes, then I have to see how I do it now. The cables are riveted to the clamps. I have to see how I remove them. Laying the foil will of course be faster then, I think. I just wonder if anything would happen to the cables under the moisture barrier and if it is correct that the cables are riveted again to the moisture barrier afterwards (holes)?

Another question:
The foil (Gefitas 300) is self-adhesive on the sides. But if I have to cut the foil every 5 meters, then at the beginning (at the cut point) I don't have any adhesive, only on the sides. How do I bond that then?