ᐅ Soil report for a 140 sqm bungalow – additional costs for waterproof concrete?
Created on: 8 Sep 2022 10:41
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EinmalimLeben
Hello!
This is my first time writing in the forum, and I’ll briefly introduce what we are planning/building:
- Bungalow with solid construction, 140 sqm (1,507 sq ft), without a basement, developer-built, building site in Lower Saxony, contract already signed and planned with the architect from the construction company.
Currently, we are preparing the building permit/planning permission application and have the soil report available. Therefore, we need waterproof concrete (WU concrete), and our developer estimates about 130 euros per sqm (square meter) of the house’s external dimensions; the final price can only be calculated after the structural engineering and material selection phase.
My questions: is there an alternative to WU concrete? Is this the same as a “white tank” (waterproof concrete structure)? I thought this wouldn’t be necessary since we are building without a basement? Is the cost estimate realistic, or what are your calculations? Since we are building to KfW40 energy standards, insulation is required—what additional costs should we expect approximately?
Thanks for your help!
This is my first time writing in the forum, and I’ll briefly introduce what we are planning/building:
- Bungalow with solid construction, 140 sqm (1,507 sq ft), without a basement, developer-built, building site in Lower Saxony, contract already signed and planned with the architect from the construction company.
Currently, we are preparing the building permit/planning permission application and have the soil report available. Therefore, we need waterproof concrete (WU concrete), and our developer estimates about 130 euros per sqm (square meter) of the house’s external dimensions; the final price can only be calculated after the structural engineering and material selection phase.
My questions: is there an alternative to WU concrete? Is this the same as a “white tank” (waterproof concrete structure)? I thought this wouldn’t be necessary since we are building without a basement? Is the cost estimate realistic, or what are your calculations? Since we are building to KfW40 energy standards, insulation is required—what additional costs should we expect approximately?
Thanks for your help!
EinmalimLeben schrieb:
Thank you very much for the very detailed answer!
We will ask if a perimeter drainage is possible.
We had four boreholes, one at each corner of the house. I have attached the third borehole. They all look similar. As mentioned before, if the soil composition doesn’t allow sealing a building without a basement against ground moisture (W1.1-E or W1.2-E), it simply won’t be done. The required permeability coefficient that the soil must meet is 10^[-4] m/s (this applies to coarse sand/gravel).
If, for example, the foundation is placed on a gravel cushion, then a permeable subsoil is present at a sufficient depth. The design water level can be lowered and a seal according to W1.1-E (ground moisture) is possible.
I’ll give a simple example:
e.g., 90cm (35 inches) of frost protection material (F1 gravel)
- Frost protection is ensured (no frost barriers necessary)
- Widespread soil improvement (the bedding modulus can be increased, even though it is already quite good according to the report => potentially less reinforcement and no strip foundations necessary)
- Sealing according to W1.1-E is sufficient
Before I would pay the additional €130 per m² (really additional?), I would reconsider the foundation or, as recommended above, try using a drainage system.
Best regards
VAT is simply passed on 1:1?!
€100 equity to €150 selling price... that won’t really work as a 1:1 pass-through.
I would probably take the slab from the house builder, even if it’s expensive. If you do it differently, they will always give you trouble with the warranty, because everything will be blamed on the foundation slab or your idea, I think.
€100 equity to €150 selling price... that won’t really work as a 1:1 pass-through.
I would probably take the slab from the house builder, even if it’s expensive. If you do it differently, they will always give you trouble with the warranty, because everything will be blamed on the foundation slab or your idea, I think.
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EinmalimLeben13 Sep 2022 23:57So, we had a callback from the home construction company yesterday. The costs are gross and represent additional expenses. He didn’t reveal much about the alternatives. We are advised to contact the geotechnical engineer directly. The exact final costs will only be possible after the structural analysis.
EinmalimLeben schrieb:
So, we received a callback from the home building company yesterday. The costs mentioned are gross and represent additional expenses. They didn’t share much about alternative options. They advised us to contact the geotechnical engineer directly. The exact final costs can only be determined after the structural analysis. That makes sense; naturally, they pass the responsibility to the geotechnical engineer since they need to guarantee that the solution will be durable.
So, contact the geotechnical engineer and ask about possible alternatives. I already provided you with a few key points. If nothing suitable comes up, I would consider getting a second opinion. A new report costs around 1,000 € (about $1,000) and is therefore cheaper than 18,000 € (about $18,000) in additional costs. I can say with 100% certainty that many other engineers wouldn’t even consider waterproofing according to W2.1-E.
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EinmalimLeben15 Sep 2022 13:14@Cronos86: Thank you very much for your response once again!
I spoke with the geotechnical engineer today, and when I mentioned drainage, new possibilities actually opened up. I was advised to check with the local authority. I did so. They are no longer responsible, but the water management authority is. After calling them, I found out that it is allowed! The responsible staff member is on vacation until Monday... The geotechnical engineer is now updating his report to include the possibility of drainage. According to him, the additional cost for drainage would be about 5,000 euros (about 5,000 euros (approximately $5,500)) instead of 22,000 euros (about 22,000 euros (approximately $24,000)) for waterproofing. That would, of course, be fantastic!
I spoke with the geotechnical engineer today, and when I mentioned drainage, new possibilities actually opened up. I was advised to check with the local authority. I did so. They are no longer responsible, but the water management authority is. After calling them, I found out that it is allowed! The responsible staff member is on vacation until Monday... The geotechnical engineer is now updating his report to include the possibility of drainage. According to him, the additional cost for drainage would be about 5,000 euros (about 5,000 euros (approximately $5,500)) instead of 22,000 euros (about 22,000 euros (approximately $24,000)) for waterproofing. That would, of course, be fantastic!
It would of course be great if that works out. I’m glad I could help.
It’s just a shame that you have to approach the soil expert as a "layperson" about such alternatives. You would actually expect this to be included in their scope of work.
You can keep us updated on what the final outcome is.
Regards
It’s just a shame that you have to approach the soil expert as a "layperson" about such alternatives. You would actually expect this to be included in their scope of work.
You can keep us updated on what the final outcome is.
Regards
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