Costs for building an outbuilding

How does it look if you build the house bigger instead of having an outbuilding and a basement? It’s probably significantly more expensive than a smaller house including a basement?

Well, exactly what the sqm costs at your provider. Just have them make you an offer.

Ok, I assumed 100m². 54m² for €125,000 means €2,315/m² (so roughly as expensive as regular living space) For the basement, I calculate about €800/m² of usable space. Your outbuilding is therefore 3 times as expensive as the same area as a basement. Basement seems to be worthwhile!

The 125, however, are completely equipped with all connections, wastewater, there is about 20 m of distance to cover. So, it is not that expensive. But the concrete solution would also be cheaper in another location.

Hm... 70TEUR for (gross or net?) 100sqm basement with pressing groundwater? ... I would like to express cautious doubts that this will be appropriate.

We have an extra charge of around 30K for WU and Wohnen.

The heat generator must also be located within the heated envelope. That means heating in an outbuilding, which is uninsulated (typically a garage or similar), is not feasible without heating in the same room and insulation, etc. Additionally, there are earthworks required to bring the heat into the main building and the losses incurred in the process ...