Foundation positioned incorrectly, what to do?

Wait a moment. Before going off on such a massive tangent.

It is about the strip footings under the formwork blocks. NOT about the floor slab. This has not yet been poured.

that is how it stands in your first post

look here :) (characters characters characters)

However, I understand it to mean that only the casting has not yet taken place, but the formwork is "complete" in the wrong place and should be poured that way, but then extended so that the finished floor slab reaches the correct position. The house would then stand on the intersection of both areas, partly on the wrong slab and partly on the extension; the unnecessary part of the "wrong" slab should then be used as a terrace. The construction phase I of the slab would thus lie under the warm house and the cold terrace; and conversely, the house would be partly on slab construction phase I and partly on slab construction phase II. That sounds like tomfoolery to the taste and on the level of @goalkeepers’s favorite neighbors :-(

It’s about the strip foundations under the formwork blocks. NOT the floor slab. This has not yet been poured.

Which formwork blocks again - to which building(part) are they supposed to belong?

I understand it as the strip foundation being correspondingly extended and the floor slab being poured correctly in one piece. The 3 meters that go back into the garden are to remain. I have no knowledge of statics, but my gut feeling says the extension is OK. The piece attached at the back, however, cannot be insulated and represents a thermal bridge. At least in my opinion. He will want to leave it as is because demolition means opening the foundation and the steel would be exposed. This leads to corrosion and possibly the "bursting" of the foundation in many years. Consult a professional! From YOUR side. Until then, construction stop.

A building stop can only come from the authorities – and you can be thankful if you never have to hear that word. But I also understand it the way does. I actually knew of a construction project with two staggered semi-detached houses (back then, they still allowed themselves such architectural gimmicks); something was misplanned, and they had to additionally pour a slab at one corner, the other piece was too much. But since hardly anyone talked about thermal bridges in 1998, they didn't make a problem out of it. The house still stands. I would get the expert/appraiser to see what they think about it. You don't have one, do you?

Since there still seem to be some misunderstandings in parts: The slab has not yet been poured. The house would also not later stand on a slab that is too large. This is "only" about the strip foundations under the slab or the formwork blocks.

We do not have an expert. The structural engineer is currently calculating the necessary work to correct the strip foundation.

How much would a demolition of the same approximately cost?

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How much would a demolition of the same approximately cost?

For you, it should actually cost nothing since it was not ordered by you, and of course you can demand the restoration of the original condition. If you have it buried again, then it is your personal concession, a favor you are doing the construction company. That’s how I see it.