XPS panels basement insulation - no bitumen layer

If this is stated like that in "official" product datasheets, then the processing company must comply. Period! This makes the discussion about the load case "draining seepage water" unnecessary – which you would have to prove in case of doubt. If you have a white tank, I would see that as unproblematic, but you haven't mentioned anything about that.

Yes, I think we have a white tank.... in-situ concrete (waterproof) and then the slabs on top....

Yes, and I would also first think like you: please process according to the manufacturer’s instructions... However, I have also noticed that with other things this only applies theoretically, for example with the studded membrane.... everyone somehow does it differently anyway

From personal experience: decided because the shell builder, architect, and construction supervisor believe that the panels do not require this additional item due to the pressure from the soil and the waterproof concrete basement.

oh thanks Zaba, that takes away some of my worries that I must have been completely crazy to trust the construction supervisor and shell builder ... today, however, an expert will come again for safety reasons

WU concrete is impermeable to liquid water but not to water vapor. According to the "shot glass formula" (an S-glass amount of water per day and square meter), some water may diffuse through WU concrete. This is then "vented away".

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We have - also in the basement - a controlled residential ventilation system, so this is already provided

Yes, I think we have a white tank....

Sorry - that sounds somewhat naive. You know something like that. Who was responsible for the planning?

From personal experience:

Only that in our case the cellar will be below ground level. One thing is the DIN-compliant solution (bitumen thick coat), the other is the practical solution. We had the choice with or without (also on a slope). The variant with would have cost us €3,000 net more. We decided against it because the shell builder, architect, and construction supervisor are of the opinion that the slabs, due to the earth pressure and waterproof concrete cellar, do not require this additional measure.

With clayey-silty soil, I would have my doubts. We built ourselves under such conditions; the soil really transports a lot of water after rainfall, and for several days. At the neighbor's house, the water then stands up to 1.80 m high at the cellar. The insulation has to be quite firm so that it does not "float." More than half of the buildings with cellars have had or currently have problems with penetrating water (some were even excavated again). At least under such soil conditions, I would have invested the €3,000 instead of knowingly accepting a construction that does not comply with recognized technical standards and possibly causes a genuine defect. If the cellar is then always slightly damp, you have a corresponding commercial depreciation when selling...

Sorry - that sounds somewhat naive. You know such things. Who is responsible for the planning?

With clayey-silty soil, I would have my doubts. We have built ourselves under such conditions; the soil really channels a lot of water after rainfall, and for several days. At the neighbor's, the water then stands up to 1.80 m high against the basement. The insulation must be quite firmly fixed so that it does not "float". More than half of the buildings with basements have had or have problems with water ingress (some were excavated again). At least with such soil conditions, I would have invested the 3,000 euros instead of knowingly accepting a construction that does not comply with recognized technical standards, which may cause a genuine defect. If the basement is always slightly damp, you have a corresponding market value reduction when selling...

We have a slope in the building plot. How should the water stand there? It still goes further down away from the house, right? The soil report is now available, so I can discuss the matter again with the shell builder and the architect.

Sorry - that sounds somewhat naive. You know things like that. Who is in charge of the planning?

I would first have to check the exact relevant passage in the offer from the shell construction company, what exactly is written there.... it will hardly say "white tank"....