Contract for cellar construction - masonry

There is news.

The basement is not mandatory, but is probably economically sensible because: The property was part of an old landfill for household waste from the 1950s. The household waste was burned and then distributed over many areas. Among others, on the site.

Now the city says: If you want to build something there, it is not allowed on filled soil that was not originally there. Therefore, everything on which a house is to be placed must be completely excavated and transported to a landfill.

A civil engineer of the general contractor has already estimated this and said that before filling the hole again, compacting it, and putting a floor slab on it, it costs about the same to build a basement.

Further details are to be provided by the soil survey after the land purchase. What is necessary and makes sense in which form.

Why do you dislike concrete basements? The statement of the general contractor is: We can do it, but concrete "sweats." Therefore, no polystyrene insulation makes sense, which would then rot away. A masonry basement would be built from 36.5 cm aerated concrete blocks and is therefore virtually already "insulated."

We will commission a soil survey after purchasing the property.

Yes, have fun.... we will find you again in a year in the defect subforum ...
Read something yourself
About black and white tank ... I have rarely heard such nonsense!!!
My concrete basement is bone dry and of course not insulated with Styrofoam but with XPS, who suggested that nonsense to you???

I would definitely advise against that. Do yourselves a favor and have the soil survey done BEFOREHAND..

(Can you say exactly where that is? Possibly also by PM if you don’t want to say it publicly. I can hardly imagine building on a landfill.)

Regards

The previous property owner guarantees to cover all additional landfill costs arising from the soil. This will also be included in the notary contract.

I consider that fair.

Soil assessments have already been done. However, for the entire property area. - It will be divided again. Therefore, none specifically for the area where the house will later be situated.

The city has also conducted one before designating the property as building land.

According to the city’s report, it is a "... area for agriculture ..."
and "... former landfill area for household waste, slag, ashes, construction debris, and excavated soil ..."

Previously, a natural stream was routed underground. During renaturation, they reopened it and in doing so "...
a large part of the old deposits was removed and properly disposed of." (1990s)

Furthermore, in the determination procedure (2015): the property falls under "... Class 2 - no danger with current/planning law usage ..." in the contaminated sites register.

Sounds to me not like a dream of soil, but also not super serious.
Especially since this is not the first property there. In the area - which entirely falls under the above-mentioned circumstances - there are several dozen single-family and multi-family houses of different ages.

I expressed myself poorly here. Sorry. I was thinking of styrofoam. The difference to Styrodur was not known to me. In fact, just "insulation" was meant.

I have the feeling we are getting off-topic.
It would help me to learn something about basement construction.
I am unsettled by conflicting opinions.
Also, there does not seem to be just _one_ "white tank" type. Rather, it depends on the respective load cases.

So:
Either a masonry basement sealed with bitumen is offered.
Or, on request, a concrete basement "white tank" which probably can be realized cost-neutrally or with a small surcharge.
Or a slab foundation, which probably causes the same costs as a basement through excavation and backfilling work.

The work is supervised by a TÜV employee ("construction supervision"). The offer describes: "Phase II. Inspection and examination of basement waterproofing before filling the excavation pit."

What should I pay attention to in the offers and discussions?
Do masonry basements now withstand ground moisture for decades? What can I, as the builder, pay attention to during construction?
The same for concrete basements: do they "sweat" and cause a humid climate?
Also here: what can I pay attention to during construction? I can imagine that if they get/have cracks, water penetrates more easily than in bitumen-sealed masonry?