Do we need an expert for possible consequential damages?

Should the floor retractable ladder be installed there later?

Yes, that is correct

I also believe that you are worrying too much here. The moisture can simply escape upwards. The foil has to be opened there anyway for the stairs. Nevertheless, the expert is always helpful. We would not have wanted to do without him.

I also think... Now invest once instead of saying in 5 years "I should have"... and then it gets really expensive

Moisture can nicely escape upwards.

Not really. Where upwards? A pure ridge ventilation does almost nothing. With these amounts of water, buckets of water first condense on the inside of the roof covering and then rain down onto the mineral wool. If this becomes more than just superficially wet, which is to be expected, it will not dry out again within a year due to lack of capillary action. In my opinion, mold damage is inevitable if the insulation is not then replaced.

Today we had an on-site appointment with the site manager... among other things, we climbed up to the attic together. I did not get the impression that the floor or the insulation lying on the floor was damp. The wood was a bit clammy and cold, but this condition could also be due to the current weather. The hole will be closed shortly. He said that this would only really become a problem once the house is properly heated through and the moisture can currently escape upwards without any problem. At the moment, the house has a temperature everywhere anyway. Of course, we should continue to ventilate. However, we will still attend tomorrow’s inspector appointment... but the conversation has already somewhat reassured us... you never know^^