Plot in flood protection area - Not recommended?

Good morning everyone,

unfortunately we are still looking for a plot of land because the last one did not work out after all. We have found a new one that is favorable in many conditions and we are therefore considering applying. The "catch" is that it is located in the flood protection area (protection up to HQ100) and for HQextreme it theoretically lies in the flood zone. However, as far as I understand, during development it is already being filled so that even the ground floor is above the projected flood level. Nevertheless, a 0.5 m high retaining wall must be built for the existing buildings and the remaining height difference should be sloped. Besides the flood risk, this immediately raises concerns when I think about the earthworks. Can anyone report what the cost implications might be? Has anyone built in a similar area before? I mean the impact on costs should be significant when considering earthworks for slopes and retaining walls, construction of a waterproof basement, etc., right? The development plan even stipulates:

It should be mentioned here that certain uses are excluded in endangered floors and the choice of appropriate building materials. Also, a flood-adapted foundation and building equipment, the sealing of supply and disposal lines, and – crucially – the securing of installations for electricity, gas, or oil tanks should help to avoid later damage and hazards.

Does that mean a) I am definitely not allowed to develop the basement as "living space" (just theoretically) b) I absolutely have to secure the basement/floor slab against buoyancy and properly found it?

As far as I can judge, when considering the 0.5 m high retaining wall, a slope approximately 1.35 m high and 4.4 m deep over about 34 linear meters also has to be created. Thus, even if the final height will have been reached during development, more than 200 m³ of soil must still be "handled."

Given these facts, should one keep clear of something like this?

Best regards

The next costs are then the exorbitantly high building insurance, if you can even find one that covers flooding...

I wouldn’t do it – and certainly only without a basement.

I could imagine building there. Hopefully, the price of the land is low enough to offset the costs of the special foundation? A basement is out of the question. On the contrary, the motto would be to go high. Raise the house and preferably put it on stilts.

If you look at the old houses along the Elbe in DD [Heimat], they were built from the start so that the ground floor can be flushed out with a hose if necessary. Important things are quickly carried up to the upper floor, and after the flood, the ground floor is flushed out, repainted, and restocked. Well, almost.

The next costs are then the exorbitantly high building insurance, if you can even find one that insures against flooding at all...

I wouldn't do it - and certainly only without a basement.

Do you have concrete experience with the insurance and how much the additional costs can be? Just to get a feeling...

I could imagine building there. Hopefully, the price of the land is cheap enough to offset the costs of the special foundation? A basement wouldn't be an option. On the contrary, the motto would be to go high. Raise the house and ideally put it on stilts.

If you look at the old houses along the Elbe in DD (hometown), they were built in such a way that the ground floor can be flushed out with a hose if necessary. Important things are quickly carried upstairs and after the flood the ground floor is flushed out, repainted, and furnished again. Well, almost.

Well, I wouldn't say the land is particularly cheap because of that... How much cheaper should it be to take the "special foundation" into account? I think we're talking about 100,000 in additional costs? Or am I completely wrong?

Would build without a basement. Just talk to neighbors or other residents in the area. They know what measures they took and what was subsequently improved. And above all, how often and how high the water actually rose.

How much cheaper should it be to take "Spezialtiefbau" into account? I think we're talking about 100,000 additional costs here? Or am I completely wrong?

Of course, it depends on the size. We cannot know what the situation is like on site and how big and long the slopes, etc. are. 100 grand seems generally a lot to me. I would have expected something around 40 to 50 instead. But it can vary so much. You need a specialist on site to assess the situation.