Very difficult topic, that's why you won't find anything concrete about it on the internet.
The pricing is tiered as follows: slab foundation, utility basement, living basement.
With a living basement, you usually don't have to dig as deep into the ground and thus have lower costs for disposing of the excavated soil. BUT this advantage is quickly offset by more expensive windows, heating, and insulation. If you plan with a KfW loan, you have to fulfill additional requirements for the living basement (which gets expensive).
No one can quantify the costs of earthworks until you have a soil report. Only then do you know on what ground you are building or founding. The costs for earthworks are the most exciting part of the whole house construction.
We are building with a slab foundation. We have a relatively flat plot and initially estimated about 5,000 € for earthworks. Well, now our hope is that it won't exceed 15,000 €. We have to partly fill up to 1m with gravel. With the naked eye and little expertise, you don’t see the 0.7% slope on the plot. I thought a bit of gravel on top and it would be fine.
A basement can cost anything from 30,000 to 70,000 depending on the soil and whether you need a "white tank" or have to get rid of water in some other way. If your soil is hard rock, it gets more expensive; if your soil does not carry, it gets more expensive. If you are not sure, I would have a soil report made and then get several offers from basement construction companies for a 10x10m house on your plot. That way you see where the journey could go.
We have consciously decided against a basement because nowadays you really don’t need one anymore. The heating and building technology is small enough to accommodate in a 4-8 sqm room on the ground floor. Instead, we invested in more ground area for the house and a larger garage.
I hope this helps you a little.
