How much additional cost according to the structural engineer's calculation?

With the standard house, the "architect" obviously has much less to do than with individual planning. It's piecework.

The provider has no obligation to inform you in advance about the necessary extras for your plot. He only has to make clear what is included in the contract. You are overwhelmed by the matter and urgently need someone who knows about construction contracts and can tell you what additional costs are coming your way and whether you have a chance to cancel the contract, change it within reasonable limits (if trades are removed, the planned profit usually remains with the company), change the planned construction or arrange additional financing.

We were recommended by the construction company to remove trades, but that doesn't improve our situation either.

Would you like to post the relevant passages here? Especially the part about the cellar and the additional costs?

I still find it dubious what they mean by that. As I understood you, they told you that a bitumen sealing was included, then you had to pay extra for a black tank, now even more extra for a white tank?

That seems strange to me, since I always thought the bitumen sealing IS the black tank. And a white tank is per se not an upgrade: these are two different methods that each have their pros and cons. One disadvantage of the white tank, as far as I know, is also that it is more difficult to make and must be executed very precisely, because otherwise your cellar might not be waterproof.

If someone contradicts me if I am wrong. I am not 100% in the subject, but that already sounds dubious.

If you have to go through with the contract, it is all the more important that you get someone on board who knows about construction and supports you. Doing this on your own with the money you have is, in my opinion, dangerous. In the worst case, you will have been charged your money (and it's a lot), and have a half-finished house or a construction ruin.

Also, someone who knows about construction law would not be bad, but that does not necessarily make things financially easier. Regarding the contract, the child is already in the well.

"Would you like to post the relevant passages here? Especially the part about the cellar and the additional costs?"

We don't have that in writing yet, but as soon as I have it, I will post it.

I have to say that h&h had stated in the documents that it might be necessary to have a tub and that this would result in considerable additional costs.

We don't have that in writing yet, but as soon as I do, I will post it.

That doesn't really add up somehow? What do you mean by documents? You signed a contract with them, and you surely also received a copy of this contract document? Everything is legally regulated in there – if their contract is compliant with the law. Only an experienced lawyer can tell you that. Normally, the contract states which documents are part of it. For example, in our case, a construction service description was also named as a contractual basis, and of course, we were given that as well. It specified which works are included in the contract. Everything not "included" is at your expense. What the signed documents (not any advertising brochures) say about the topic of the basement would be of great interest to us here.

I don't understand you. You are walking straight into disaster with open eyes and digging yourselves in deeper and deeper. At first, you were incredibly naive, which is stupid. But now you are making no effort to tackle the problems and get out of the hole again. It is not crucial when the factory planning begins. What matters is that you can afford to pay for the construction.

I don't understand you. You are walking with your eyes wide open into disaster and digging yourselves in deeper and deeper. At first you were incredibly naive, which is stupid. But now you make no effort to tackle the problems and get out of the hole again. It doesn't matter when the factory planning begins. What matters is that you can pay for the construction.

Yes, I don't get it either. Surely five people have said here that it would be wiser to exercise the right of withdrawal rather than waive it. If the person seeking advice then does exactly the opposite, you can't help him/her.

but that we are in earthquake zone 3 they could have told us beforehand or we should have informed ourselves better.

The company is a national one, right?! How are they supposed to know at the time of contract signing that you are in an earthquake zone 3?
They only take care of everything once the soil survey is available and the planning begins. So step by step.

I have to say that h&h had in the documents that it might be necessary to have a tub and that then considerable additional costs could arise.

Yes sure: a house/house construction is being sold. The house is initially always without a basement according to the construction performance description. In the basement clause (if desired) it then says that this and that can lead to additional costs.

Someone contradict me if I’m wrong. I’m not 100% on the subject, but that already sounds dubious.

In principle, I do not consider it dubious. Just like, for example, TeamMassiv promises its "more-than-cheap price" but after two years comes with the understandable excuse that the bricks or whatever are no longer available and thus significantly more additional costs come to the builder.
Basically, the construction company is not obliged to repeatedly point out every part of potential additional costs. Otherwise, they would be sitting at the contract table for several more days. It is stated in the contract and in the construction performance description. Then the builder is also obliged to have the contract checked if clueless or, like many of us, to ask about this and that in a forum.
What H&H has in the contract, we do not even know. To me it just reads like a lot of naivety.
I can somewhat relate, although for us it did not concern the basement, but additional effort for the foundation slab and earth removal.

they said they cannot start with the site planning otherwise.

This also reads like a lot of naivety here. I can only say that it also surprises me, after several warnings have been given here, that you just blindly continue and not only proudly look into the financial abyss but even take a step forward.

also a construction performance description was named as the basis of contract, and of course it was handed over to us as well.

That is even mandatory.