ᐅ Soil replacement up to 1.20 meters deep – raise the ground level or build a basement?

Hello everyone,

I was informed today in a preliminary phone call by my geotechnical engineer that the existing soil on our plot is likely not load-bearing and therefore unsuitable for construction. It will need to be replaced (I don’t have the full report yet, so I don’t have more details) – and this to a depth of at least 1.20 m (4 feet).

We had originally planned to build a house with 2 full stories and no basement on the plot (house footprint about 11.5 x 9 m (38 x 30 feet)). Since the surface of the plot is currently level with the street, my layman’s understanding is that we would need to refill the 1.20 m (4 feet) deep excavation with more load-bearing material so that the ground floor remains at street level. Alternatively, we are now considering digging a bit deeper and installing at least a partial basement instead of refilling.

Since I don’t have the report yet and haven’t obtained any quotes from excavation contractors: does anyone here have experience with the costs for excavation and especially refilling of soil on this scale (1.20 m (4 feet) depth, footprint about 105 sqm (1,130 sqft))? And, for comparison, what would be the approximate cost for excavating a full foundation pit for a basement including the basement itself (cast-in-place waterproof concrete basement shell, "white tank")?

Of course, I understand that this can only be a rough estimate of what this might cost in our case. However, since all the information I’ve found online so far is already 5 years or older (and prices have not decreased since then), I would really appreciate current figures as a reference.

Thank you very much in advance!

We had to excavate 1 meter (3.3 feet) deep until stable soil was reached. Then, a gravel layer about 60-70 cm (24-28 inches) high was installed and compacted. The strip foundations were placed on top of that. Some of the soil was backfilled between the strips and around the strip foundations. Our plot is slightly sloped, and we use the remaining soil to fill in, at least as much as we need. The concrete slab is 90 square meters (970 square feet), and an additional area for the double garage measuring 6 by 9 meters (20 by 30 feet) was added. We paid 23,000 euros for the earthworks, including site drainage. If any soil needs to be removed, this cost will be added.

For each cubic meter of soil excavation, we are charged 35€ for digging out and transporting by truck to the landfill. However, this always depends on the soil quality (the LAGA value is indicated in the soil report if it is part of the contract).

Of course, this varies by region, also depending on the different distances to landfills.

Thank you very much for your responses!

The 23,000 sounds quite reasonable, @vanny2705. Could you please tell me in which year and approximately where that was? We are in the immediate vicinity of Frankfurt, so it will probably be somewhat more expensive there compared to, for example, rural areas...

I’m less concerned about the excavation itself; I’m more interested in getting a sense of the costs for backfilling and compaction (in relation to the costs of a basement).

The figure is current; we have just paid it. We are located in a rather rural area, in case you know the OWL region.
We didn’t even consider a basement because we definitely didn’t want one, and our builder said a basement is very expensive.

Thank you! In the Frankfurt area, I would expect costs around 30,000 to 40,000 Euros. Depending on how much of that is for backfilling, a basement might not be that much more expensive...

For a house without a basement, I would still need to excavate about 125 m³ (11.5*9*1.20 m), which is roughly 125 cubic meters. If I estimate excavation and disposal at 45 Euros per m³, that amounts to just under 5,700 Euros. The majority of the cost, let's say around 30,000 Euros, would be for backfilling and compaction, totaling about 35,000 Euros.

For a basement, the excavation pit is larger. Roughly estimated (and if anyone with more expertise reads this, please feel free to correct me), for a floor plan of about 11.5x9 m, the excavation for a basement might be around 435 m³ (14.5x12x2.5 m). Excavation and disposal would then cost around 20,000 Euros. Add the basement construction costs of approximately 30,000 to 40,000 Euros (according to online research, the average price for a prefabricated basement is about 300 Euros per square meter), making the total about 50,000 to 60,000 Euros.

An extra 20,000 Euros for a basement doesn’t seem too bad after all...