Unauthorized high-quality work - additional costs

Hello Ypg, sorry about the initial confusions. The construction is almost finished, now the final invoices are coming. We are building with a general contractor. The construction contract states a fixed price and says the production costs include all costs up to the turnkey completion of the construction project. I had thoroughly reviewed the contract and found few unexpected/disadvantageous clauses for me. There is nothing stated about additional costs (except planned special requests) that may arise.

I actually see only two possibilities to get around the payment:

1.) The soil survey was prepared in advance and is an explicit contractual component with the general contractor (GU) (thus the GU knew about the requirements for the sealing and included them in the contract). Whether the survey is part of the contract is stated in the contract between you and the GU.
2.) The chargeable better sealing is not required according to the soil survey

Otherwise, you could demand an exact breakdown of the pricing, how they arrive at €5000 for a bit more material and a few hours. The whole thing probably actually costs only €1000 and the rest is once again the "take it or leave it" surcharge...

The general contractor (GU) apparently has a lump sum contract with a fixed price. This means he has to construct the building according to the recognized rules of technology and calculate accordingly. Such changes in details do occur. Ultimately, this is the entrepreneurial risk of the GU. It might have been correct if the GU had immediately raised "concerns about the planned execution" (sealing only against non-pressing water) and had this execution approved or offered a change. But then the question arises who planned it incorrectly and whether the report was available.

For supplements, it generally applies that they must have the same calculation basis as the main contract. In case of doubt, you can ask the GU to provide evidence for this. Fantasy prices for supplements are often accepted by homebuilders. I wouldn’t put up with that.

The general contractor apparently has a lump sum contract with a fixed price. That means he has to construct the building according to the recognized rules of technology and calculate accordingly. Such changes in details do occur. Ultimately, this is the entrepreneurial risk of the general contractor.

I strongly doubt that this is the case. No company sets the clauses in a way that puts themselves at a disadvantage. The general contractor owes the customer a house according to the construction specification and nothing more. Somewhere it will certainly say that the price only applies as long as nothing has to be different from the construction specification. The general contractor cannot possibly factor in all eventualities because he simply cannot know what conditions prevail on the property. Of course, unless the soil survey was carried out beforehand and is part of the contract. Because then the general contractor knew what he was getting into and accordingly the surcharge would not be justified. The probably best approach would be a direct conversation with the site manager or someone similar. Since you are so sparing with the information, there are few tips that can be given. Before handing over the matter, you could, for example, let it slip that you will complain about every little thing (tile offset 0.5mm over tolerance: new and such jokes) and ask for a reasonable solution. A reasonable one would be if the construction company only charges you the cost of the materials (probably around €1000) because they botched the usual process (order...) Otherwise, you just threaten years of legal disputes (you didn’t order that…), which they absolutely have no desire for. Overall, the chances are pretty good that you will come out with a significantly reduced bill.

The general contractor owes the client a house according to the scope of services and nothing more.

If the execution according to the scope of services is technically insufficient, and the general contractor could have been aware of it (an expert report was available), then the general contractor must execute according to the recognized rules of technology (sealing according to DIN). Of course, I assume that the detailed planning was done by the general contractor. Alternatively, he can execute according to the scope of services if the client explicitly requests this and is informed about the consequences. This must be documented, and I cannot imagine that this was the case. Ultimately, it is decisive whether the expert report was available to the general contractor in time, i.e., whether he planned incorrectly or someone else did. If in the end there are objectively justified claims, they must be examined carefully in terms of amount.

you say the same as I do. the GU just had to have known at the time of signing that the additional effort was necessary. this proof is provided by the [bodengutachten], which became part of the contract at the time of signing.

since the [bodengutachten] was definitely not available on that day, he could not have been aware of it. the only thing that can be blamed on the GU now is that he did not get the OK/order for the additional costs. and that could significantly reduce the costs, since the GU surely does not want to have a legal dispute.