Which type of basement construction is preferred?

Hello everyone,

until recently, I thought there were only the two options for basement construction: "black tank" and "white tank," besides the alternative of "no basement," of course. In the meantime, I have found out that there are apparently also "brown tanks," and particularly cautious (anxious??) people build a sort of black-white or brown-white tank, meaning they additionally seal the actually white tank with bitumen or bentonite mats.

So far, I always thought the white WU tank made the most sense, as it is at least as watertight as the black tank and also cheaper. Apparently, however, the white tank is not completely safe against water vapor. I don’t know if that is a big problem. In any case, I read more and more from people who additionally seal their white tank with bitumen or bentonite to be on the safe side. Basically, not a wrong approach but it should also have a significant cost impact.

In addition, there is discussion about the proper insulation for the basement floor. Most insulating materials are said to get wet over time despite claimed water resistance because they absorb water vapor. Only the (somewhat more expensive) cellular glass apparently gets only advantages and no disadvantages. Which also seems suspicious to me.

So what do the very cautious do? They build a white tank, have it additionally sealed with bitumen or bentonite, then hang the cellular glass insulation in front of it and also, of course, seal that again with foil and bitumen. Sounds safe to the layman at first, but do you really need that or is it seriously overdone?

I am interested in the opinions of the gathered (prospective) builders. How did you build? How will you build? What are your experiences? Have you perhaps regretted choosing a certain setup? I am curious...

As for the white tank and the diffusion of water vapor, all I can say is: I thought the same before. Then I informed myself thoroughly and came across, for example, an experimental setup at TU Berlin and a publication from the "InformationsZentrum Beton". Both can be found quickly via a Google search (unfortunately linking is not possible here in the forum).

Conclusion from both: If the wall is thick enough, no water transport takes place from outside to inside. Whether liquid or vapor form.
I believe according to WU standard the walls are at least 20 cm thick, if not even more. In our case (Schwörerhaus) it is 24 cm. We decided on a white tank (not heated) with perimeter insulation as a DIY project.

Additionally, you must also consider how the humidity inside the (possibly even unheated) basement looks. Hanging laundry there would probably not be such a good idea.
Of course, it is also important how you want to use your basement. There are residential basements or, in contrast, pure utility basements. Surely there is something in between... that should also be taken into consideration.

And last but not least very important: What kind of situation do I actually have on site? How humid is it? Slope location? Standing or pressing water? What type of soil? How may drainage be done?