Basement construction at high groundwater level (2m)

Hello everyone,

this is our first... house and therefore we lack some experience. The soil survey showed a groundwater level of 2.2m (in high summer). Throughout the year there are certainly also levels of around 1.6m. Otherwise sandy soil.



We would like to build a basement anyway, with small windows possible above. A lower ceiling height of 2.2m would still be acceptable for us; it is not supposed to be a living basement.

Our question now is whether it is still financially possible to build a basement.

- How deep is an excavation pit usually dug?
- Does anyone have experience with how much more expensive a basement can/will become due to too high groundwater?
- Any other advice?

Many thanks!

Here, a white tank is often assumed at a flat rate of 80-100 TEUR.
Whether a white tank is sufficient or additional measures are necessary, I don't know.
Given the groundwater level, I would seriously reconsider the basement. Even if money is not an issue (in that case, you could simply build bigger or taller), a white tank will not remain waterproof forever. It is practically constantly in the water, and groundwater also pushes upwards. That is something different from rainfall slowly seeping away.
Depth:
2.2m clear room height
+20cm floor slab (if that is enough)
+10cm insulation (actually more)
+ 2cm finished floor
So at least 2.5m, meaning that it already stands in water up to the beginning of the wall if you don't want to build the ground floor significantly elevated.

Excavation pit itself even deeper, since probably a gravel screed should be made despite the sand.

Unless according to 's basement rule a basement seems indicated anyway due to the slope (then rather as a lower ground floor, meaning at least for the open side with residential basement equipment), I would really just leave it.

Our question now is whether it is still financially possible to build a basement.

We do not know your financial framework conditions, so nothing can be said about the possibility.

Information about the desired use and whether the basement makes sense or whether the floor area should rather be increased is also missing.

- How deep is an excavation pit usually dug?

How deep should the house be dug into the ground? In the past, basements were often only half-buried. And then it also depends on the thickness of the foundations and load-bearing layers and possibly insulation. Contact architect + structural engineer.

Does anyone have experience with how much more expensive a basement can/will become due to too high groundwater?

Very, very roughly 20k.

Other advice

"A drill is not just a drill"

If, according to @11ant's cellar rule, a cellar does not seem to be indicated anyway due to the slope (but then rather as a basement, i.e. at least for the open side still with residential cellar equipment), I would really just leave it at that.

By the way, you can currently read it on "Bauen jetzt," as a four-part series: last week the first 11ant cellar rule regarding the question of cellar yes or no, the day after tomorrow it will be about partial cellars, next week about residential cellars, and the week after next about technical cellars and the summary of which stance to take on the cellar question in which terrain situation.

"A borehole is not just a borehole"

That's true, but don't we already have the "worst case"?

Regarding groundwater control. The groundwater must be lowered to at least 0.5 m below the deepest excavation base. Lowering depths of 0.5 m are still conceivable with open water control. For greater lowering depths, closed water control (vacuum lance or similar) must be planned. This becomes quite expensive. In addition, neighboring buildings can be affected by the lowering. Securing evidence in advance is absolutely advisable (if there are neighbors). Then there are also discharge fees for the water. And significantly longer construction time.

I don't even want to mention the costs for sealing... If you don't have to rely on it, I wouldn't put myself through that. Or go so deep into the ground that the intervention is minimal.

Thanks already for the answers!
There were a total of 2 boreholes and it looks the same there, as well as a groundwater measurement point nearby that measures similar values.

Whether a white tank is enough or additional measures are necessary, I don’t know.
With that groundwater level, I would seriously think about the basement. Even if money is no problem (then you could just build bigger or higher), a white tank will not keep watertight forever. It basically stands in water all the time and groundwater also pushes upward. That is something different from when precipitation slowly seeps away.

So far, I assumed that I would need a white tank anyway, but that it is simply "watertight" and you could basically build it in water – is that not the case?

We do not know your financial framework, so nothing can be said about the possibility.

Information about the intended use and whether the basement makes sense or if the floor area should rather be increased is also missing.

Financially we are doing well, but a basement "at all costs" makes no financial sense if, for example, you could build the house bigger instead. The plot allows for a bigger house, but actually living space is more expensive again and it would be nice to just have this basement.

Basically, it is meant for technology, sports room, storage space, hobby room.

I had hoped that if you raise the basement a little, it would still be cheaper than increasing the living space of the house. But as you describe it and as I feared, the construction measures are especially expensive and incalculable.