Soil replacement up to 1.20m depth - fill or basement?

Hello everyone,

I learned today in advance by phone from my soil expert that the existing soil on our property is apparently not load-bearing and therefore not suitable for construction, but must be replaced (since I do not yet have the report, I have no further details) – and this down to a depth of at least 1.20m.

We had originally planned to build a house with 2 full floors without a basement on the property (footprint of the house approx. 11.5x9m). Since the surface of the property is currently at street level, this would mean, from my layman's understanding, that we would also have to refill the 1.20m deep hole with something more load-bearing so that our ground floor remains at street level. Alternatively, we are now considering whether instead of refilling, we could dig a little deeper and build at least part of the house with a basement.

Since I do not yet have the report and have not yet obtained any offers from excavation contractors: does anyone have experience with what the excavation and in particular the backfilling of soil to this extent (1.20 m depth, footprint approx. 105 sqm) might cost? And how does this compare to the cost of excavating a full foundation pit for a basement including the basement (white tank)?

Of course, I understand that all this can only be rough estimates of what the costs might be in our case. However, since the information I found on the internet is all at least 5 years old (and prices have not exactly fallen since then), I would appreciate current figures as a reference.

Thank you very much in advance!

We had to excavate 1 meter deep until load-bearing soil was present. Then a gravel layer about 60-70 cm high was laid, which was compacted. On top of that came the strip foundations. Part of the soil was placed back between the strips and filled around the strips. The plot slopes slightly on our side, and we use the remaining soil to fill in, at least as much as we need. The slab is 90 sqm and additionally, there was the area for the double garage of 6x9m. We paid 23,000 Euros for the earthworks including [Grundstücksentwässerung]. If any soil still needs to be removed, that cost will be added.

For us, 35€ per m³ of soil excavation costs are incurred for digging out and transporting by truck to the landfill. However, it always depends on the soil quality ([LAGA Wert] is stated in the soil report if commissioned).

Of course, this varies regionally, also influenced by different distances to landfills.

Thank you very much for your answers!

The 23,000 sounds quite okay, . Could you also tell me in which year and approximately where that was? We are in the immediate vicinity of Frankfurt, so it will probably be generally a bit more expensive there than, for example, in rural areas...

I am less concerned about the excavation itself; I am more interested in getting a feel for the costs of filling and compacting (in relation to the costs of a basement).

The number is current, we just paid it recently. We are located in a rather rural area, in case OWL means anything to you. We didn’t even bother with the Thema Keller because we definitely didn’t want one and our builder said a basement is very expensive.

Thank you very much! Then I would rather expect around 30-40k in the Frankfurt region. Depending on how much of that is for backfilling, a basement probably wouldn’t be much more expensive...

For a house without a basement, I would have to excavate about (11.5*9*1.20m =) approximately 125 m3 anyway. If I assume 45 euros/m3 for excavation and disposal at the landfill, that amounts to almost 5,700 euros. The lion’s share would then be for backfilling and compacting, let’s say 30,000 euros, a total of about 35,000 euros.

For a basement, the excavation pit is larger, roughly estimated (if anyone reads this who knows more than I do, please feel free to correct me) with a floor plan of about 11.5x9m, the excavation pit for a basement might be approximately (14.5x12x2.5m =) about 435 m3.
For excavation and disposal, that then amounts to about 20,000 euros. Plus costs for the basement of about 30,000-40,000 euros (according to internet research, the average price for a prefabricated basement is 300 euros/sqm), totaling 50,000-60,000 euros.

20,000 euros additional cost for a basement wouldn’t be too bad then...