Building in existing structures - Subsequent additional costs despite a fixed price

The building permit has been granted. What difference does that make for you?

I just wanted to know what the equivalent of the 50k is. Presumably, the payment plan states 10% of the construction sum after approval of the building application. The contractor presumably waited specifically for the payment before registering the additional costs. That is not fair business conduct. I would take the argument from into account. I also think that the rejection strengthens your position. Then wait and see what happens. Nevertheless, you should at least ask a lawyer how your position is contractually. Only they know all the documents. See post #31

Is there already a additional cost notification with a written justification? Without this, I would not conduct any negotiations. And only then would I talk to the lawyer. In no case should you sign anything immediately.

There is an additional cost announcement, here called "supplementary agreement" amounting to almost 18,000 EUR. However, we have not signed it yet because the description read: "Reinforcement of existing foundation according to DIN4123 - 18,000 EUR. To be paid with installment XY." That was insufficient information for me to accept, and I have already requested a concrete list of all covered activities. The foundation work is actually supposed to begin next week. I am now somewhat concerned that "we just don't sign this now and simply wait to see what happens" might come back to bite me. Or does it actually play into my hands, since they have now already scheduled all other trades and work, and it would be a huge organizational effort for them to hit the brakes?

You should ask the entrepreneur why he believes that the supplementary agreement should not be covered by the fixed price.

A brief update. The responsible site manager has now given us an ultimatum. Either we sign the additional agreement regarding the foundation reinforcement immediately, the updated version of which we only received yesterday, or the start of construction/demolition, which is supposed to begin next week, will automatically be delayed by one month and we will have to pay a flat rate for higher material costs in addition. We have an appointment with the managing director next Tuesday. An appointment with a construction law attorney hopefully on Friday. Is such an ultimatum legitimate?

What does your contract say regarding delays and cost increases caused by the builder?

It makes sense that the work / workers need to be scheduled for next week, right? They don't say to themselves on Monday morning: "Alright. 17 people are here, where shall we go today? Any suggestions?"