ᐅ Soil replacement up to 1.20 meters deep – raise the ground level or build a basement?
Created on: 7 Jul 2020 19:52
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BananaJoe
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!
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!
BananaJoe schrieb:
For a basement, the excavation pit becomes larger. Roughly estimating (if anyone with more expertise reads this, please feel free to correct me), for a floor plan of about 11.5 x 9 m (38 x 30 ft), the excavation pit for a basement might be approximately 14.5 x 12 x 2.5 m (48 x 39 x 8 ft), which equals about 435 m³ (15,340 ft³).
Additional costs for the basement excavation would therefore be around 310 m³ (10,950 ft³) x 45 Euro (estimated) = approximately 14,000 Euro for excavation and disposal. More likely around 600 m³ (21,190 ft³), since the soil loosens after digging and you end up with more volume to transport. Have you already received the 45 Euro/m³ as a binding offer from an excavator for your soil classification? Otherwise, you might face an unpleasant surprise.
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BananaJoe8 Jul 2020 14:50@Scout: Thanks for the note about the larger volume.
No, all the figures are still just rough estimates at this point. I can only request reliable quotes from the groundworks contractor once I have the survey report that specifies the soil classification. I’m just trying to approach the topic and the calculations in principle...
No, all the figures are still just rough estimates at this point. I can only request reliable quotes from the groundworks contractor once I have the survey report that specifies the soil classification. I’m just trying to approach the topic and the calculations in principle...
BananaJoe schrieb:
Thank you! In the Frankfurt area, I would estimate around 30,000 to 40,000. Depending on how much of that goes into backfilling, a basement might not be much more expensive...
For a house without a basement, I would still need to excavate about (11.5*9*1.20m =) 125 cubic meters (about 4,414 cubic feet). If I assume 45 Euros per cubic meter (about $45 per cubic yard) for excavation and disposal at the landfill, that comes to almost 5,700 Euros. The bulk of the cost, around 30,000 Euros, would then be for backfilling and compaction, totaling approximately 35,000 Euros.
For a basement, the excavation pit is larger. Rough estimate (if anyone with more expertise reads this, feel free to correct me): for a floor plan of about 11.5x9 meters, the excavation for a basement would be around (14.5x12x2.5m =) 435 cubic meters (about 15,343 cubic feet). Excavation and disposal would then cost roughly 20,000 Euros. Adding about 30,000 to 40,000 Euros for the basement itself (according to online research, the average price for a prefabricated basement is 300 Euros per square meter), the total comes to 50,000 to 60,000 Euros.
An additional 20,000 Euros for a basement doesn’t seem too bad... That still doesn’t include screed, electrical work, heating, floor coverings, painting, and doors.
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goalkeeper8 Jul 2020 16:20Your 50-60k for the basement including excavation and disposal is definitely too low – for us (end-terrace house) it was around 45k (local general contractor) – without disposal for a 7x10m (23x33 ft) house size. In your place, I would rather estimate 70-80k for the basement.
By the way, we had similar ground conditions as you and also built strip foundations.
By the way, we had similar ground conditions as you and also built strip foundations.
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BananaJoe9 Jul 2020 11:40OK, I can see now that I have probably been too optimistic about the basement...
I’ll put that idea back on the shelf for now and may only bring it up again once I have the survey report and the quotes from the excavation contractor...
Thank you all for your feedback!
I’ll put that idea back on the shelf for now and may only bring it up again once I have the survey report and the quotes from the excavation contractor...
Thank you all for your feedback!
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Matthew039 Jul 2020 14:21BananaJoe schrieb:
OK, I can see now that I may have been a bit too optimistic about the basement....
So I’ll put that idea back on the shelf for now and maybe only revisit it once I have the report and quotes from the excavation contractor...
Many thanks for all the feedback!...and then also factor in the reduced space needed on the ground floor and/or upper floor if you save space by placing technical installations in the basement—you might save a few square meters (square feet) upstairs...
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