Euro/sqm: Which square meters count?

Hello, I am currently trying to inform myself about the possible costs of a new build that might closely resemble our current house. The guideline value of 2000€/sqm for the costs of the house is always mentioned. However, it has not become clear to me which square meters are to be included, especially when a basement comes into play. In our current house, for example, we have a relatively low knee wall in the attic and the house has a basement (built on a slope, therefore basement with entrance/hallway, guest room, utility room, and a double garage).

Do the pure floor plan square meters count? In our case that would be 3 floors x 8mx11m = 264sqm x 2000 Euro/sqm = 528,000?! That can’t be right. But even if the basement is excluded, we would already be at 350k. According to the living space calculation, it is rather 144sqm (on the ground and attic floors), which at just under 300k is still far from the catalog offers of prefab house providers, but at least goes in the direction of "only 50% of my worst fears"...

And I know that the topic of basements is hard to quantify, but basically: Is a basement on a slope with a garage generally cheaper to estimate than one that is completely underground? In any case, you save the 20-40k for the double garage.

The basis for the 2000 euros/sqm as the first benchmark is the targeted living space sqm. In addition, the incidental construction costs are added

The basement is then to be calculated separately. This is quite different, of course .. basement costs, for example on sloping sites, will replace some costs from earthworks (embankment) etc.

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Okay, that sounds reassuring. With a healthy dose of pessimism, 100k for the land, 80k for additional construction costs, 70k for the basement, a house for around 320k, and 30k for outdoor facilities would not be a bad basic calculation. It's still 600k, but far from the feared 750k.

The basement becomes more expensive if a) the thermal envelope runs within the basement, which would be the case with an internal garage b) the basement is converted into living space. So be careful. However, the ancillary building costs are relatively generous.

A large part of our "basement" will be converted into living space (slope house). Therefore, your calculated 70k will not be enough for that. If you want to create living space in the basement, for example an office or something similar, I would at least calculate 2000EUR per square meter. A garage in the basement is an expensive venture. We also had it calculated and will prefer to use the basement as living space and build a garage next to the house. Incidentals in construction costs I find generous but not overpriced. They will, of course, increase significantly due to the basement construction and the associated excavation. Also, the question is what you include in those costs (kitchen is not yet included in your list and usually costs 15-20k).