Low concrete cover in the basement "white tank"

A real white tank involves quite a bit more, I won’t list all of it now. Back to your soil survey again. I find it quite surprising that the groundwater was found at 19m. I remember the heavy driving survey with a max. depth of 7m. What were they looking for down there, oil? Whatever.

Not 19 m (I remembered incorrectly), but 25-27 m. Quote from the soil survey: After completion of the exploratory work on 15.01.2021 and 01.02.2021, no water level could be measured in the explorations up to the maximum exploration depth of 3.00 m below ground, i.e. -2.76 m relative height. Only in pit SCH 1 was a groundwater horizon encountered at a depth of 1.20 m below surface level. According to the Bavarian State Office for the Environment /U 9/, the groundwater level in the area of the construction project is stated as approximately 303 to 305 m NHN or 25 to 27 m below ground in the bedrock (sandstone).

What does the soil survey say about the sealing of earth-contacting structural parts such as basements in general? There must be something like: "cohesive soil, therefore temporarily standing/pressing layer water, load case 1, therefore recommendation for watertight construction" or something similar.

It does not say "white tank" directly in the soil survey, but it is a new development area and all neighbors here only build white tanks. There are already neighbors who did not build a white tank and already have water damage in the basement.

Okay. Let's look at the whole thing objectively again:

No one here except you knows the exact wording in the contract.
No one here except you knows the exact wording in the soil report.
Before you waste unnecessary time or make a hasty decision based on well-meant advice here from the forum (including me), consult an expert.

We also did not think it was possible that this could happen to us, but we too had to take up the cause and commission a specialist to review it.

It is about 1) a technically flawless basement and 2) a lot of money.

Only an expert will be able to comprehensively assess your situation and tell you what you can do now. The forum at most soothes your soul or puts you into panic. Neither will get you any further.

Is this a precast basement?

Is the house already built?

Who determined the concrete cover and how?

In my opinion, sealing only the joints is nonsense. The minimal concrete cover is presumably present in the wall area.

Renovation, price reduction, 30 years warranty and warranty retention (bank guarantee) is the minimum.

The expert will tell you exactly how the renovation should be done.

It is a basement made of in-situ concrete. The basement is not yet finished. It should be insulated soon and the excavation pit backfilled. The concrete cover was determined by an engineering office using reinforcement scanning (Hilti PS 200 S Ferroscan). The minimum concrete cover is located in the lower plinth area of the basement exterior wall (outside), immediately above the base slab.

Are examples of repairs and the amount of price reduction known?

The engineering office that measured the concrete cover is your contact person. They should be able to tell you how to properly carry out the renovation. The structural engineer of the contractor has already named you 3 options. Legal questions are best clarified with a lawyer.

Renovation, price reduction, 30 years warranty and warranty retention (bank guarantee) are the minimum.

Depending on how large the actual deviation is from the target deviation and depending on how technically critical the whole thing is at such an early stage of construction, you might also consider a demolition. This can and should be clarified by the expert. If applicable, you may have a lifelong exclusion from the residential building and natural hazard insurance if the basement does not comply with the technical standards. After 30 years (which in practice are also very rarely accepted by the general contractor), you bear the risk fully yourself for the rest of your life. If you sell the house before that, you will have a huge price reduction on the entire house if you must disclose that the basement does not meet the requirements of the applicable load case.

In short: It is not about the value of the basement but about that of the entire house with land and the lifelong risk of damage occurrence arising from the basement.

By the way, we are facing the same dilemma, but it is already the roof on the shell that makes the matter more difficult.

The engineering office that measured the concrete cover is your contact. They should be able to tell you how to carry out a professional renovation. The structural engineer of the contractor has already mentioned 3 options to you.

Legal questions are best clarified with a lawyer.

If I understand correctly, the engineering office was not commissioned by the original poster but by the contractor. Therefore, I see little point in asking them about renovation options now.

Your contacts from now on should be the expert and, after determination of the facts, possibly also – as the colleague already said – a lawyer.

By the way, I personally sympathize with you; in our case, the "worst case" has practically been confirmed, and we are alternating meetings with experts and attorneys. Therefore, my urgent advice: turn to an expert, preferably publicly appointed and sworn, as no one should question their neutrality here and their statements would also stand in court if necessary – which does not mean it has to come to that.