From when is the fixed price no longer changeable

Hello We signed our house contract last year and contractually agreed on a fixed price guarantee until 11/2021. Construction began about 2 weeks ago and no increase has been announced or indicated yet. Could it still happen that the construction company raises the price afterward or was the fixed price set in stone with the start of construction?

Could it still happen that the construction company raises the price afterwards

Yes, it can.

was the set price carved in stone with the start of the construction?

No, there is no dependency behind that.

Who is responsible for exceeding the deadline for price fixing?

Who is responsible for exceeding the deadline for the price guarantee?

In our opinion, the construction company is responsible for the delay due to omissions and planning errors. The building application was supposed to be submitted in August 2021... but this only happened in October 2021. The building application was also submitted incomplete by the construction company, so that we partly had to send our own documents to the building authority to avoid further delays. There were also some planning problems, as the windows we wanted could not be implemented, but this was only communicated to us 3 months after the planning. In the last amendment regarding minor changes, we also received a current order amount of xxx€ which corresponds to the price of the fixed price guarantee with the issue date of 18.03.2022.

We signed our house contract last year and contractually agreed on a fixed price guarantee until 11/2021. Construction began about 2 weeks ago

In our opinion, the construction company is responsible for the delay due to oversights and faulty planning.

That sounds in any case like you should make your explanations much more detailed (that's why they're called that, *LOL*).

In the last addendum, regarding minor changes, we also received a current contract amount of xxx€ which corresponds to the price of the fixed price guarantee with the issue date 18.03.2022.

Why don’t you write that right away? Then, in my opinion, it is more likely that the fixed price still applies. But if you should receive a change to the fixed price, can you prove the delay caused by the contractor? In today's situation, it can always happen that you can expect a price adjustment. At least recently, some such cases have come in here. But hopefully you have good arguments (evidence) that the contractor is responsible for the price increases himself.