13 sqm larger house 30,000€ additional price

The "small" house is a city villa with 133 sqm. The larger version is identical in floor plan etc., just 13 sqm bigger with 146 sqm. [...] Some rooms are not even half a square meter smaller, so we ask ourselves whether the additional price of €30,000 for 13 sqm is really justified/necessary.

That is nonsense or rather a wrong perspective: it is not an additional price, but a price difference. It would be an additional price if in the 146 sqm model you could not see a version of the 133 sqm model (just like a Golf is a standalone model and not simply a Polo that is X cm bigger in every single dimension), but the 133 sqm model would be extended by 13 sqm along the ridge axis. The crucial point is whether, after

We are almost at the end of all our planning

it would be found that the 133 sqm model pinches anywhere (if not, then tick it off and close the case).

If I understand the initial post correctly, it is about some kind of model or prefabricated house that comes in the same floor plan in two sizes (this is quite common with the major prefab house companies). If this assumption is correct, the 30K is genuine profiteering: we had a similar situation and the house builder offered 14K (and even that was already significantly above the costs derived from the quantities). If I see it correctly, there is quite a margin in the 30K. To what extent you can negotiate it down, only you can assess. I would consider what the 13 sqm are worth to me and would politely, constructively, and open-endedly present this to the provider. If they are cooperative, they can move noticeably. Good luck!

Oh, I see! If the 30 TEUR also includes the proportional costs for extra paint, tiles, other floor coverings, etc., that is not included in my calculation. I have basically only ordered up to screed and plaster... but it still seems rather high to me.

I'm glad that we found a regional general contractor who is not on the prefab house rip-off track..

30k for those few extra sqm?? That's not realistic but complete rip-off.

We increased from 150 to 160 sqm (basically just increased the house by about half a meter on each side and that’s it).

It was exactly 11,000€ in extra costs.

If I understand the original post correctly, it's about some kind of model or prefab house that comes in the exact same floor plan in two sizes (this is often the case with the big prefab house companies). If this assumption is correct, the 30K is actual extortion: we had a similar situation and the house builder offered 14K (and even that was already significantly above the costs resulting from the quantities). If I see this correctly, there is quite a bit of leeway in the 30K. How much you can negotiate down depends only on you. I would consider what the 13 sqm are worth to me and politely, constructively, and openly communicate this to the provider. If they are cooperative, they can move noticeably. Good luck!

No, this is actually a solid stone-built house. The story behind it is that at the very beginning the house was offered with 146 sqm, but at that time it was too expensive for us and we asked to make savings where possible. That’s how the smaller house came about. Over time and various discussions, however, some changes were added again, a kind of mixture of the two houses. Ultimately, the exterior views and floor plans, etc., are identical except for the size difference of 13 sqm. The 30,000€ refers to the entire house price (larger foundation slab, bricks, paint, flooring, etc.).

We increased from 150 to 160 sqm (ultimately, the house was expanded by about half a meter on each side and that was it). The additional cost was exactly €11,000.

If you mean by that half a meter more on one side in the eaves and on the other side in the (more elaborate) gable dimension, then that is quite affordable.

The story behind it is that at the very beginning the house was offered with 146 sqm, but at that time it was too expensive for us and we therefore asked to make savings where possible. That is how the smaller house came about.

So only the size 146 was an original catalog model and the 133 version was created as a budget variant, which is "naturally" not noticeably smaller in all places (?) – then I would rather recommend the "larger" (or rather: un-reduced) "original" because it has the more tested detail connections.