Construction costs are currently skyrocketing

I think there are only few contracts that include such a clause. It might be possible to wriggle out through a failed financing in the case of the higher amount or to hope for the goodwill of the seller/company. Basically, both contracting parties expect security – the client with a fixed price commitment and the builder through the customer's signature.

My husband and I probably made a mistake in the contract or did not consider something due to lack of time: We hadn’t had a sampling yet, thus no construction plan either. The fixed price was only set for 18 months, after that the total price increases by 0.4% per month, but only for a maximum of 6 months. After that, the price list valid at the time of acceptance applies. :-( Well, in the worst case, we just have to pay the 5% to get out of the contract again, because the price at the time of acceptance in the next (worst case the following) year is likely to be unrealistic. We have to take the blame for the construction permit taking longer than expected; the other side is responsible for it taking months until a sampling appointment and that it was not possible to get a sampling appointment before the construction permit was granted.

In newer contracts, there is usually a clause stating that material price increases above x % result in price adjustments. I also know that construction companies for wooden houses pay their customers 25,000 € if they withdraw from the contract. In the case of a price increase of 100,000 €, the contractor cannot, in my opinion, insist on compliance with the contract nor demand a withdrawal fee, since the cause does not lie with the client. My limit for the contractor to insist on contract compliance would be an increase of 10 %, as is generally possible with craftsmen's invoices.

Well, in the worst case, we just have to pay the 5% to get out of the contract, since the price at the time of acceptance next year (or in the worst case, the year after next) is likely to be unrealistic.

One can only hope that all this will balance out again. The question is, if you cancel this contract, what then? Building with someone else probably won’t be any cheaper. And if you give it up entirely, you’ll have to pay the bank a lot for the unused loan. And that would be for nothing. Not a good solution either.

I also know that construction companies for wooden houses pay their customers €25,000 if they withdraw from the contract.

I've heard that too. Even sums around 50,000 EUR…

Are you aware of whether, or from which purchase price increase one can withdraw from an already concluded house purchase contract?

Why do you want to get out of the contract? Do you no longer want to build after all?

and it was not possible to get an appointment for sample selection before the building permit was issued.

Huh? That wasn’t doable? Why not?