I had the subsurface conditions on our plot investigated. Four soundings were carried out using a light dynamic probe.
The inspection report states that a 20cm (8 inches) natural gravel base layer should be installed beneath the concrete slab to improve the soil. The total cost for this is €3,500 gross.
Since I’m not an expert, I would be interested to hear your opinions. What are the pros and cons?
The inspection report states that a 20cm (8 inches) natural gravel base layer should be installed beneath the concrete slab to improve the soil. The total cost for this is €3,500 gross.
Since I’m not an expert, I would be interested to hear your opinions. What are the pros and cons?
I cannot assess the term "natural" in "natural gravel layer" versus simply "gravel layer."
Arguments in favor:
- I am not aware of any concrete slabs without gravel underneath (though I am not a true expert).
- Gravel can act as drainage, allowing surface water to infiltrate the gravel layer fairly easily, preventing the slab from being constantly waterlogged.
- This is only somewhat effective if your groundwater is already close to the surface near the lawn edge.
- Gravel generally serves as a leveling layer to compensate for settling and erosion.
- A specialist was specifically consulted who considers the gravel layer necessary.
- No construction company will dare to do anything different if this expert report exists.
Arguments against:
- It costs money and is pointless if the expert is just trying to overcharge you.
- If you don’t believe that, then the question about the value of the gravel layer is basically already answered and irrelevant.
I cannot evaluate the costs; in our case, the gravel layer was included in the offer and the concrete slab.
Arguments in favor:
- I am not aware of any concrete slabs without gravel underneath (though I am not a true expert).
- Gravel can act as drainage, allowing surface water to infiltrate the gravel layer fairly easily, preventing the slab from being constantly waterlogged.
- This is only somewhat effective if your groundwater is already close to the surface near the lawn edge.
- Gravel generally serves as a leveling layer to compensate for settling and erosion.
- A specialist was specifically consulted who considers the gravel layer necessary.
- No construction company will dare to do anything different if this expert report exists.
Arguments against:
- It costs money and is pointless if the expert is just trying to overcharge you.
- If you don’t believe that, then the question about the value of the gravel layer is basically already answered and irrelevant.
I cannot evaluate the costs; in our case, the gravel layer was included in the offer and the concrete slab.
I am not familiar with building without it and would not consider building without it.
The question is rather why the contractor does not automatically include this in the contract? Conversely, I would imagine that many other items might also be missing and you will likely face additional costs for several aspects. For example, removing topsoil, digging pipe trenches, excavation and material transport, possibly with a surcharge depending on the soil type, and so on.
Secondly, I wonder why a gravel layer should cost 3,500 euros. I find this amount extremely high.
The question is rather why the contractor does not automatically include this in the contract? Conversely, I would imagine that many other items might also be missing and you will likely face additional costs for several aspects. For example, removing topsoil, digging pipe trenches, excavation and material transport, possibly with a surcharge depending on the soil type, and so on.
Secondly, I wonder why a gravel layer should cost 3,500 euros. I find this amount extremely high.
McEgg schrieb:
... what do you think about it? What are the pros and cons?What could be against it?
You have a geologist prepare a soil report, they provide a foundation recommendation, and the structural engineer tells you that this foundation will result in an additional cost of $3500 gross.
And now you’re asking us home builders in this forum what we think about this professional advice.
McEgg schrieb:
Since I’m not an expert, That’s exactly why you consult a geologist. The structural engineer must also be able to rely on such a report—without the geologist’s recommendation, any construction that deviates and is built to a lower standard risks being permanently unstable.
You need to start trusting the experts. Opinions in forums can vary, and sometimes fundamental technical knowledge is shared, but when it comes to engineering work like this, you can’t simply say: “I’d skip it—you won’t see it later anyway… it’ll hold up fine without natural gravel… in my crystal ball I see good soil and a geo fool…”
And even if all of us here were structural engineers and geologists, we still couldn’t say anything conclusive because we don’t know the soil conditions!
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