Embankment of land in a "flood" area

Hello everyone,

we are currently considering buying a plot of land, and I would like to hear your assessments or experiences – especially regarding additional costs or risks.

Key data:

[*]Plot size: approx. 576 m²
[*]Distance to the Danube: approx. 150 m
[*]Location according to the flood hazard map: HQextreme (information from the building plan)
[*]Price: approx. €180,000
[*]Location: Bavaria, ZIP code: 93*

Excerpt from the building plan:

“According to the flood hazard map of the Bavarian State Office for the Environment, the construction area lies in the flood hazard area HQextreme.
The soft clays of the cohesive top layer are not suitable for building foundations without additional measures, as these can lead to torsions and tilting due to unfavorable load/settlement behavior.
The at least stiff clays of the cohesive top layer, on the other hand, are generally suitable for building foundations.
If buildings are not cellar-equipped, only minor water retention measures are necessary (e.g., sump pumps, drainage pipes).
Waterproofing against pressing water according to DIN 18195-6 must be provided.
Cellars are explicitly not recommended.”

Regarding the situation:

The plot currently lies about 1.5 m below street level, so in a kind of “pit.” According to the building plan, the land must be filled up to street level.

This problem affects all parcels within the planned street – partly more, partly less. It would certainly be possible to cooperate with the future builders here.

My questions:

[*]With which additional costs for the necessary filling and soil improvement should one realistically expect (order of magnitude)? Also for the “waterproofing against pressing water”?
[*]Are there risks or disadvantages due to the location in the HQextreme zone, even if no cellar is planned? According to a neighbor (who has lived there for about 20 years), floodwaters could be well contained so far by a dam, but who knows how that will look in the coming years…
[*]Does anyone have experience with how building permits are handled in such areas (e.g., additional requirements or insurance issues)?
[*]Would you personally buy under such conditions at all?

Pictures of the development plan, Google Maps to assess the proximity to the Danube, and a picture of the “pit.”

Thanks in advance for your opinions and reports of experience!

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Are there alternatives? Consider how much all the add-ons cost, the 180000 sounds cheap probably because all other costs have been deducted!

How are insurances there? Can you get any against flood damage or do they all refuse? That would be important information, although I have to say that I personally would probably not build there, but of course that is a subjective risk assessment. Unfortunately, I cannot say anything about costs.

Are the geological surveys accessible to the municipality? Where exactly do the stiff clays of the cohesive cover layer occur?

Construction was done directly on the Danube as well.

You should ask an earthworks contractor what usable fill material (delivered and installed) costs in the area.

You always have the sealing against rising moisture.

Adjust the construction method to the situation. In my opinion, rather only massive.

[*]What additional costs for the necessary filling and soil improvement should one realistically expect (order of magnitude)? Likewise for the "sealing against pressing water"?

The big question mark, which I also cannot answer. In England and the Netherlands, I have seen houses built on a pontoon in a basin, whose level can be adjusted on supports to match a water level. Such construction methods have also been tested in the Emsland region. I do not have exact prices, but I believe I have read an order of magnitude of €200,000 for a single-family house. These houses are insurable, although the costs are somewhat higher than for a safe standard house. I would roughly estimate a 25% surcharge there. The pontoon system requires maintenance, for which I would estimate €1,500 p.a. In any case, that would be the approach I would take. For extraordinary projects, sometimes funding and similar support can be found. Just be creative.

[*]Would you personally buy under such conditions at all?

With Ponton: yes, without: rather not.