Floor plan of a single-family house with basement, 150 sqm, only single-story allowed

Good question. I told the planner 150-160sqm, to which he responded with just over 150sqm. I think this is a buffer, since with every change the area also changes. And with a good floor plan, removing a few square meters is probably almost impossible, while with a good 150sqm floor plan, you might still be able to improve something. In principle, as long as everything fits within 150sqm, we are also satisfied with 150sqm. We would gladly take the savings of €40,000 + interest. I wouldn't have considered a statement "exactly 160sqm" to be sensible.

Quick calculation: with a 10m long side and a 30° roof, raising the knee wall by 10cm already increases the living space by 3.5sqm. Therefore, you can quite well regulate this via the knee wall with an appropriate floor plan, as long as you remain one-and-a-half stories.

But I really like the earth cellar. I didn’t know the term, but I would like to build it adjacent to our cellar, which will be fully heated and insulated.

Why adjacent? – the planned full basement under the house would already be an earth cellar (as long as you leave it outside the thermal envelope). However, I would rather basement a garden shed or something similar (or place the garden shed on top of the earth cellar).

Regarding the larger house, I have to say unfortunately that this is not possible because of the subsidy. This caps at 160 sqm of living space. Since the basement does not count towards that, it is a practical extension for us. A larger house without a basement and without subsidy costs us significantly more than a 150 sqm house with a basement.

A carport back shed or a garage extension would also not count as part of the house. 160 sqm according to DIN or living space regulation? (In any case, I wouldn’t fully exploit the cap).

would already be a cellar (as long as you leave it outside the thermal envelope)

It is currently inside the envelope.

160 sqm according to DIN or the Living Space Ordinance? (I would definitely not fully exploit the cap).

According to the Living Space Ordinance - Living Space Ordinance.

Basically, as long as everything fits into the 150 sqm, we are also satisfied with 150 sqm.

Oh, and since there were still 10 sqm left, a balcony is planned, which is also proportionally included in the living area according to the Wohnflächenverordnung. I don't want to scare anyone now. Nevertheless, it must be mentioned that an office in the basement does not count as an ancillary room like a technical room. For the energy standard plus, does the basement fall within the thermal envelope? I'm not sure about that. If not, then it must be structurally separated from the heated rooms. Does that mean a closed basement staircase?! However, an above-ground technical room as well as a basement replacement room are also deducted according to the Wohnflächenverordnung. Regarding the basement with light wells in the mentioned rooms or office, it should be noted: the office may never officially be designated as a living room. The light wells could seem very constricting in case of a narrow property width, thus restricting the use of the property. But I also want to say that I don't know enough about how things are calculated there. But there are enough threads on this topic here.

Since the plot is quite narrow, you should reconsider the outdoor facilities. Carport for one car - yes, but then? Bicycles, scooter, tricycle? Second car? Most carport owners also have a lockable room attached at the back for these things. Plan it right away, otherwise it will be tight for you! You might want to turn the house around.