2.25m below street level - Cost estimation

Hello everyone,

My small family and I are still at the very beginning of our house planning and I am asking for advice regarding the upcoming decision whether to build with a slab or with a basement (single-family house ~140sqm). I have already read countless threads on this topic, so it is not about the general pros and cons but about the conditions on our property!

The fact is that our plot is 1.85 m below street level (inspection chamber RW). As part of the soil survey of the entire construction area by the municipality, a borehole was made directly at our plot (I know this does not replace a proper soil survey of the property, which can only be done after development).

According to this, the soil consists of

- 40 cm topsoil / OH / BKL 1+4
- 40 cm floodplain sand, medium dense, SW/SU (corresponds to F1), 20-25t kN/m²
- 1.20 m loamy floodplain gravel, medium dense, GU/SU, F2, 25-30t kN/m²
- 2.00 m floodplain sand/floodplain gravel, SW/GW, F1, 25-30t kN/m²
- 1.00 m floodplain gravel, GW/SW, F1, 30-35t kN/m²

Installation class Z0 according to VwV Boden BaWü. The groundwater level is at 91-92 m above sea level - street level at 100.78 m above sea level.

In other words, after removing the 40 cm of topsoil, we would be at 2.25 m below street level.

Now to our questions

- What do you fill such an amount up with?!
- Would we have to fill the entire 2.25 meters with gravel/crushed stone, or can you, for example, ask the neighbors for topsoil and only fill up the last meter with load-bearing crushed stone? What would that cost us (roughly calculated, that would be 500 m³ - meaning the front half of the plot)? The entire plot is 360 sqm...

Unfortunately, so far I have only received answers like "that would probably cost around 15-20k €". It is always pointed out that a soil survey is necessary. I am well aware of that, but it can only happen in a few months and our planning is on hold until then if we do not know whether we will build with or without a basement...

- Approximately how much would the pure excavation of the basement have cost me if the plot were at street level?

I hope I have conveyed my concern clearly and thank you in advance for any help

I can't really imagine this technically or visually: an access road so "inappropriate" to the properties adjacent to it; and: what about the neighboring plots - are they all "normal" and only a tunnel beneath yours has collapsed?

I do know fields - including some that become building land - that lie far below street level, but then that road is not also the one that serves them.

What would the pure excavation of the basement have cost me approximately if the property were at street level?

that should then cost around 15-20k €

The answer is in your text. Including backfilling and removal.

I can't quite imagine it technically or visually: an access road so "inappropriate" for the plots adjacent to it; and: what about the neighboring plots - are they all "normal" and only under yours has a tunnel collapsed?

I do know fields - including some that become building land - that lie far below street level, but then that street isn't also the one providing access to them.

It was a field area, there is a depression in the middle, meaning the plots around us have the same conditions, the others are probably then at street level.
Here is a picture...

That's cool!

You are building a "basement" that is actually fully suitable for living as a light semi-basement.

In 100 years, I wouldn't cover it up - I'd rather create vacation apartments or something else.

The terrace will just be a large wooden balcony.

Add water and the gravel pit lake is ready.