Building ground suddenly a biotope

Why are you digging out the basement again? I do not understand some of your explanations.

The basement must be underground due to the entire height of the house, but in the front we will make something like large light wells so that regular windows are possible there

What type of soil class do you have?

I unfortunately don’t know that, only that it is not contaminated. We let the construction company do everything; they gave us a fixed price and that’s it, they do the rest.

Without a soil survey, the earthworks are a lottery, especially on a slope.

Fixed prices never include things like this here:

1 to 2 meters distance from the retaining wall, a nice stone wall will be built there, the retaining wall is currently about 1.50m

You are building incredibly elaborately with many expensive extras. Are you aware of that?
Just out of pure curiosity: What is the retaining wall with drainage etc. supposed to cost?

I didn’t mean the installation class, but the soil class. You don’t have an expert report, but plan with a mystery box.
Look at your offer to see what is stated there.
Excavation disposal depending on the installation class can become very expensive. Not every landfill accepts everything. Between Z0 and
[Bodenklasse] it can become really expensive from 5 onwards.