Water damage in the basement still during construction - what to do?

Hello everyone,

we are building a semi-detached house solidly with a WU basement. The shell was already completely finished in March, currently in the finishing phase: screed poured mid-July, underfloor heating installed beforehand, interior plaster also already finished.
In August, we had both dehumidifiers each for 2 weeks.
For one week now, my neighbor has had water damage in the basement (see photo). The affected area (at least visually) is in the stairwell (so no exterior walls). Visually, nothing can be seen at my place. The water is rising from the floor, in the photo the plaster has already become soft. Last week, the basement floor at my neighbor's place was completely tiled; according to the tiler, the CM value was okay for this.
We have commissioned the water damage expert; the first findings are: significantly exceeded measurement values aw over 0.9 for both of us, he also took samples to determine where the water is coming from. The costs for this are considerable.
The construction company rejects everything at first, a meeting is scheduled on Monday at the construction site with the TÜV inspector on behalf of the construction company.

Questions so far:
1. Can the costs (expert report, samples, etc.) be covered by insurance? Which one (builder’s insurance, construction performance description - we have both).
2. It is strange that the water appeared so late and almost in the middle - floor slab crack? If this is the case, what will be the consequences for us? Complete screed removal? Can this be caused by tiling?
3. How does the search for the cause proceed?

Maybe some tips and tricks.

Many thanks!

Regards
Nils

Such a mess!
I assume there is a geotechnical report to exclude groundwater?

Can the costs (report, samples, etc.) be covered by insurance? Which ones (building owner, construction performance description - we have both).

Possibly construction all-risk insurance, do you have that?
However, I first see the construction company as being responsible.

It's strange that the water appeared so late

No, water slowly makes its way through the masonry if the cause is a leak.

How does the investigation of the cause work?

Breaking open?
Possibly, you can tell from the plans whether any pipes run nearby. Maybe it’s also a leak in the underfloor heating.

As a comparison/note: We ourselves had damage like this in the ground floor office on the walls from below. The cause was a leaking outdoor faucet; the water accumulated between the base slab and the screed and then traveled up the walls. Fortunately, we had not yet laid flooring in the affected room (guest room). Outdoor faucet repaired, dehumidifier in, and eventually it dried out.

At our house, the sealing in the basement was not done correctly and it looked like that.

If the construction company made a mistake here, it depends on how they react when you confront them with it. If they are stubborn, usually only legal expenses insurance helps.

Bauleistungsversicherungsprint only applies if, for example, it was really only the faucet.

In our house, the basement waterproofing was not done correctly and it looked like that.

Thanks for the answer! How was it technically solved in your case?

Thank you for the answer! How was it solved technically in your case?

We gave the house back to the seller (-; It was a case of fraudulent misrepresentation… went through a lot in recent years with real estate, I basically had no luck… But the owner then had the exterior excavated, which shouldn’t be a big problem for you in the shell construction, and then a company professionally sealed or injected it… of course, that was a project costing around 100,000 euros in an existing building, but it shouldn’t be a problem for you. The important thing is that the construction company cooperates… because you won’t want to move in there like that or accept the house…. Keep us updated on what the construction company says about it. If legal action has to be taken, which one tries to avoid at first, we can continue talking in that direction….

Evening,

Oops, water damage is always bad, we had that issue too, but in our upstairs after moving in.

What I don't quite understand: The house is still under construction and not accepted at all? Then it's not your problem at all, but the general contractor's.... Or have you outsourced partial trades and the general contractor now wants to claim that someone else messed up?

Best regards,

Andreas