ᐅ Basement Construction with High Groundwater Levels (2 meters)
Created on: 27 Sep 2023 11:18
P
pxrunes2
Hello everyone,
This is our first house, so we lack some experience. The soil survey revealed a groundwater level of 2.2 meters (7 feet) during midsummer. Throughout the year, there are probably levels around 1.6 meters (5 feet). Otherwise, the soil is sandy.
We would like to build a basement anyway, with small windows above ground level. A lower ceiling height of 2.2 meters (7 feet) would still be acceptable for us, since it will not be a living basement.
Our question now is whether building a basement is still financially feasible.
- How deep is an excavation typically dug?
- Does anyone have experience with how much more expensive a basement can become due to high groundwater?
- Any other advice?
Many thanks!
This is our first house, so we lack some experience. The soil survey revealed a groundwater level of 2.2 meters (7 feet) during midsummer. Throughout the year, there are probably levels around 1.6 meters (5 feet). Otherwise, the soil is sandy.
We would like to build a basement anyway, with small windows above ground level. A lower ceiling height of 2.2 meters (7 feet) would still be acceptable for us, since it will not be a living basement.
Our question now is whether building a basement is still financially feasible.
- How deep is an excavation typically dug?
- Does anyone have experience with how much more expensive a basement can become due to high groundwater?
- Any other advice?
Many thanks!
Nordlys had it the same way:
Studiobinder
Studiobinder
Tolentino schrieb:
Nordlys had it like that too: https://www.hausbau-forum.de/threads/wie-halte-ich-schimmel-vom-spitzboden-fern.39073/post-500063And even as a hip roof. However, even a man can see the difference compared to the almost purely decorative attic space from @Steffi33 :-)https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
A
Allthewayup27 Sep 2023 20:48@WilderSueden thanks for the tag.
Unfortunately, lowering the groundwater level was unavoidable for us since we only have a 300sqm (3,229 sq ft) plot and the groundwater is at -2.4m (-7.9 ft).
But back to you. Please provide me with the following values:
- permeability coefficient (kf value) from the soil report
- drilling depths
- depth of impermeable layer (if any)
- distance from excavation pit to neighboring plots
- distance from excavation pit to neighboring buildings
How large is the plot? Would you be able to live with raising the house including the basement by 2-3 steps?
Some important keywords have already been mentioned.
It is also worth knowing that no natural hazard insurance covers damages caused by permanently standing groundwater, as this is simply not insurable. A properly constructed basement built to modern standards remains watertight even when submerged for many decades and can be later waterproofed using injection methods if built in cast-in-place concrete. According to experts (and tests), this is not possible with prefabricated construction methods.
For building in groundwater, I would definitely involve an expert during planning because serious mistakes can, in the worst case, only be rectified by demolition.
The costs for your basement are difficult to estimate precisely as a flat rate.
Many say that one square meter of basement construction is cheaper than one square meter of living space above ground, for reasons including:
- lower ceiling height = less material
- no lintels, blinds, or shutters
- usually no walk-in shower, toilet, or fixtures
- generally much cheaper floor coverings
- usually less electrical installation
- partial or no underfloor heating
- less plastering effort since concrete walls are usually left unplastered
- and so on.
Groundwater lowering would have cost us upwards of €40,000 (about $44,000), so I did it myself. But if you add those €40,000 to the basement cost, the price per square meter ends up similar to the living area again, and the picture looks different.
Unfortunately, lowering the groundwater level was unavoidable for us since we only have a 300sqm (3,229 sq ft) plot and the groundwater is at -2.4m (-7.9 ft).
But back to you. Please provide me with the following values:
- permeability coefficient (kf value) from the soil report
- drilling depths
- depth of impermeable layer (if any)
- distance from excavation pit to neighboring plots
- distance from excavation pit to neighboring buildings
How large is the plot? Would you be able to live with raising the house including the basement by 2-3 steps?
Some important keywords have already been mentioned.
It is also worth knowing that no natural hazard insurance covers damages caused by permanently standing groundwater, as this is simply not insurable. A properly constructed basement built to modern standards remains watertight even when submerged for many decades and can be later waterproofed using injection methods if built in cast-in-place concrete. According to experts (and tests), this is not possible with prefabricated construction methods.
For building in groundwater, I would definitely involve an expert during planning because serious mistakes can, in the worst case, only be rectified by demolition.
The costs for your basement are difficult to estimate precisely as a flat rate.
Many say that one square meter of basement construction is cheaper than one square meter of living space above ground, for reasons including:
- lower ceiling height = less material
- no lintels, blinds, or shutters
- usually no walk-in shower, toilet, or fixtures
- generally much cheaper floor coverings
- usually less electrical installation
- partial or no underfloor heating
- less plastering effort since concrete walls are usually left unplastered
- and so on.
Groundwater lowering would have cost us upwards of €40,000 (about $44,000), so I did it myself. But if you add those €40,000 to the basement cost, the price per square meter ends up similar to the living area again, and the picture looks different.
There are already many great answers and ideas here, thank you very much!
@Allthewayup wow, thank you for the detailed response. We could make the house bigger, but since the plot is rather narrow, and for the other reasons you mentioned, I would prefer to have everything “under one roof.” And I’m afraid that if rooms like a gym or hobby room are planned on the upper floors, they are more likely to be cut than if they are in the basement.
However, the negatives are also significant; for example, I hadn’t considered the insurance issue.
Did you consider choosing a closed water table system back then? I would initially think that this would reduce surprises such as a sudden rise in the groundwater level.
Regarding the values you requested:
The drilling depths were two times 7 meters (22.9 feet) each with similar conditions. And a dynamic probing test at 4 meters (13.1 feet).
The distance to the neighboring plot is 2 or 3 meters (6.6 or 9.8 feet), respectively. To the buildings, it is 5.5 or 6 meters (18 or 19.7 feet), respectively.
The plot is over 1000 square meters (approximately 10,760 square feet), but as mentioned, narrow. We are already fully using the construction width of about 9 meters (29.5 feet).
I have also considered raising the building. In theory, building regulations allow the basement to protrude up to 1.4 meters (4.6 feet), but as others have pointed out, this somewhat blocks the ground floor. And building up earth to create a slope might look odd or could be expensive.
@Allthewayup wow, thank you for the detailed response. We could make the house bigger, but since the plot is rather narrow, and for the other reasons you mentioned, I would prefer to have everything “under one roof.” And I’m afraid that if rooms like a gym or hobby room are planned on the upper floors, they are more likely to be cut than if they are in the basement.
However, the negatives are also significant; for example, I hadn’t considered the insurance issue.
Did you consider choosing a closed water table system back then? I would initially think that this would reduce surprises such as a sudden rise in the groundwater level.
Regarding the values you requested:
The drilling depths were two times 7 meters (22.9 feet) each with similar conditions. And a dynamic probing test at 4 meters (13.1 feet).
The distance to the neighboring plot is 2 or 3 meters (6.6 or 9.8 feet), respectively. To the buildings, it is 5.5 or 6 meters (18 or 19.7 feet), respectively.
Allthewayup schrieb:
How large is the plot? Could you live with raising the house including the basement by 2–3 steps?
The plot is over 1000 square meters (approximately 10,760 square feet), but as mentioned, narrow. We are already fully using the construction width of about 9 meters (29.5 feet).
I have also considered raising the building. In theory, building regulations allow the basement to protrude up to 1.4 meters (4.6 feet), but as others have pointed out, this somewhat blocks the ground floor. And building up earth to create a slope might look odd or could be expensive.
Does the zoning plan specify a maximum number of stories? For example, are you allowed to build two full floors plus an attic, or does the zoning plan prevent that? If necessary, you could always go with the classic solution of a larger garage and use that as storage space.
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