Perimeter insulation - possibilities

Hello everyone,

we have the following problem with our new construction.
We are currently building a new semi-detached house attached to an existing semi-detached house. Since the existing semi-detached house is very old and only has a very shallow basement, we had to have a shotcrete wall built in the earth area in front of the neighbor’s existing basement.
We now want to build our basement onto this shotcrete wall, which is larger in all directions than the basement of the old semi-detached house.

However, we now have the problem that the shotcrete wall is unfortunately not flat at all, and the original plan to place our new prefabricated basement including XPS exterior wall insulation flat against the shotcrete wall does not work. Therefore, we are currently considering whether the unevenness could be "simply" compensated with another insulation that fills the cavities well between our new prefabricated house wall and the shotcrete wall, and where the insulation is not as rigid as the XPS boards. According to the Building Energy Act, we need insulation with WLS 045.
Are there possibilities to work here with any more flexible insulations between the shotcrete wall and the basement wall, something similar to loose-fill insulation, bonded insulations, or similar, to fill the cavities well?
Or could the planned exterior wall insulation possibly be replaced by interior wall insulation in the basement if necessary?

Oh, and the basement is being built as a waterproof basement (WU-Keller). Groundwater did not appear during excavation and is currently not found approximately 50cm lower; however, according to the soil report, the groundwater level is about 25cm above the bottom edge of the floor slab, so almost exactly at the height of the top edge of the floor slab (25cm thick).

The entire project with a basement attached to an existing semi-detached house and then other dimensions is already prone to errors in itself - but others here know more about that.

For the insulation, I would not use loose fill in the ground. They are also not approved for that purpose. As an alternative to XPS boards, if they do not lie flat, there would be PUR/PIR as blown-in insulation after the prefabricated wall is in place. The material is poured in liquid form and then foams up, penetrating every cavity. It is basically like construction foam. However, it is significantly less pressure-resistant than XPS. But if that is sufficient, it would be a cavity-filling, non-rotting alternative that can also be used in the ground. The thermal conductivity value (WLS) is by the way 028 for pure PUR, so that should be more than enough.

Thank you very much for the explanations. That already helps. Can you fill something like this in yourself, or should it be done by a specialist company? Do you possibly have an exact product name for such insulation?

Our energy consultant otherwise recommended a Bituperl loose-fill insulation, but that is also only WLS 060.

If a cleanliness layer of lean concrete is applied at the bottom, a loose fill insulation would no longer have contact with the ground. Maybe that would work then? Completely foaming sounds expensive.

We have a lean concrete blinding layer. It was just constructed last week and is flush against the shotcrete wall. Therefore, there would be no contact with the natural ground below, but theoretically on the sides, if nothing is built in front of it.

Oh, right, finished elements form an enclosed space by themselves. I personally didn’t know that backfilling with soil isn’t possible. But when thinking about it, it makes sense, since roots can penetrate much more easily there and can thus destroy both the insulation itself and, through consequential damage such as water ingress, the insulation.

In that respect, the backfilling would likely have to be sealed all around, and then the question would be whether, in the end, the foam injection variant from isn’t actually simpler and even cheaper. Strange that your energy consultant didn’t know that either.