Determine floor structure in the bathroom - trial drilling performed

Hello forum,

the bathroom on the first floor in our detached house built in 1990 is to be renovated. A walk-in shower without a raised step should be installed if possible.

Before starting, we wanted to find out whether this is even reasonably feasible. For this purpose, I made a test drill and concluded the following layer structure from it:



I have the following questions about this:

[*]Does the floor structure appear possible or correctly determined? The "nothing" layer is probably styrofoam or similar.


[*]In which layer is the drain of the existing raised shower tray presumably installed, in the "nothing" or the concrete below?


[*]Should the entire floor structure be removed for a thorough bathroom renovation?


[*]Or leave the floor as it is, only break it up in the area of the future shower, otherwise glue new tiles over the existing tiles?


[*]Is there anything (obvious) speaking against installing a walk-in shower?

Thanks in advance for opinions/tips!

Werkheimer

Normally, the process should be nothing.

First, remove the old shower. Under the old shower, there was only a big hole.

The old shower is a "surface-mounted" model, approximately 17cm above the tiled floor.

Yes, it was the same with us. But what good does it do you to speculate? In the end, it depends on how it looks in the shower.

It is about the preliminary planning for the entire bathroom, which should not only start once the shower has been torn out. Therefore, I would actually need practical experience with typical floor constructions -- and regarding the above questions.