Improve floor plan - how?!

145 sqm are absolutely not XS - but a square shape is always a handicap for a floor plan, and the edge length of 950 is, in my opinion, clearly the pain threshold for the floor plan to still work. The house is also not absolutely too small, just relatively so for the differentiation of the floor plan: a study room is already a burden for the allocation of the area here, separating bed and wardrobes is also, and a children's bathroom (which you at least omitted) would be out of the question.

That you received no alternatives is not entirely true: I at least mentioned the models Edition 134 and Evolution 134 from the same provider. And I seem to recall that I had already suggested taking a model with a non-square rectangular floor plan as a basis. By the way, your floor plan is (double swear!) typical for a "town villa," so I nearly fell off my chair that your house provider regularly builds a "country house" version on that basis.

Heating technology is clearly not a layman’s matter; other average citizens rarely have it as a hobby either. Therefore, I found it especially important to point out that if you still need to educate yourself on this anyway, the various options cannot be ranked linearly as better or worse, but each technology is optimal in relation to the targeted energy efficiency level of the house – and also the note that the house provider understands more about this than the customers but does not share his superior knowledge with them without also being guided by his own interests. What calculation might be behind advising you away from the "town villa" with the claim of 30,000 EUR additional costs, I cannot yet speculate. In principle, that is at least a fib, because what makes the "town villa" so affordable is not least its cheap roof. By designing it as a knee wall house instead of a "town villa," a significantly more expensive roof structure is required. The difference is basically structural. The understandable lay logic that knee wall 180 is more expensive than 160, 200 even more expensive than 180, straight wall (= practically knee wall 250) should thus be even more expensive, is a misconception (which providers gladly exploit repeatedly to steer customers with surcharge fears toward the house they want to sell them). You can hardly orient yourself here by either; “solid” calculation is different again. Also, the regional "solid" general contractors preferably offer "town villas" in the economy segment. In reality, the "town villa" cannot be more expensive – on the contrary! – rather, only the provider can make it more expensive in his calculation. That should then only motivate you to look around with other providers!

Not an option or idea, but that is how we will take over the plot.

That is, when you bought the plot, the filling up had simply not yet been done, but was already included in the purchase price?

Yes, I had overlooked the prefabricated house part.

145 sqm is absolutely not XS - but a square shape is always a liability for a floor plan, and in my opinion the edge length of 950 is clearly the pain threshold at which the floor plan can still work.

*Mathematics digression: Take a rectangle and specify its area. Then you can give one side, e.g. the length, and the width is determined accordingly. When building a house with a certain area in mind, that is basically the approach. Now the square is the one among all rectangles with the same area that has the smallest perimeter (i.e., the shortest exterior wall). Furthermore, the center point (intersection of the diagonals) is farthest away from the nearest exterior wall. Mathematics end* For the floor plan, this means that there is relatively little space for windows (less than in any other rectangle with the same area) and these are also far from the center of the house (so there is an area in the middle that is hard to illuminate with daylight). I think that makes designing square floor plans somewhat more demanding. If there is no reason for the square, I would probably lean more towards a moderate rectangle. One very basic question: if you have already signed a contract, isn’t the house type already fixed? Are you allowed to change it? Depending on the contract content, this possibility may not be a given.

I think your math course is good and also correct in terms of content. However, the lack of space for windows here results from the knee wall and not because of the perimeter or the available exterior wall area. A square is indeed more difficult in terms of layout in the floor plan, but this is not due to the perimeter, rather to the resulting room shapes and the stair positioning or the necessary hallway shape.

10x10 results in a 40m perimeter
8x12.5 results in a 41m perimeter

This is not the decisive factor when it comes to the windows.

I think that makes designing square floor plans a bit more challenging.

No, the difficulty in floor planning with the requirement that it should be a square rectangle lies in the fact that the rooms to be accommodated have the trouble that not all of them either want to be square themselves or, alternatively, as much narrower than a square as the neighboring rooms want to be wider. This inevitably leads to a) squeaking and creaking at every corner and end, b) rooms with held breath / sucked-in bellies, c) rooms that curve around each other until the wall layouts are as winding as in a labyrinth. If a bulky object is then added (cooking island, straight staircase, walled-in bedroom closet area aka "dressing room"), the floor plan either bursts with a loud bang or you have to concede space to relieve the pressure – where easily 30% of "love handles" are added to the actually needed (and financially affordable) area. What you can achieve very well with an "Anstatt" villa on a square plot – and that’s why it is so popular with construction companies – is: a pleasing illusion of a successful home, which, spiced up with a handful of fashion accessories, appeals to a broad customer base. Additionally, you simply get a facade-optimized thermal envelope, hence the nickname "KfW cube".