Is it sensible to use a dehumidifier after taking over the building or just ventilate by opening the windows?

So, I’m talking 7 days about dryers that were as big as spreaders, that had a fixed hose and permanently drained into the shower or the sink. Never 350,- Euro. Karsten

We borrowed some from the painter for the upper floor, 2 pieces at 12€ each per day. In the good 10 days, the two of them extracted 400 liters of water from the air. For the whole house, you would rather need 4.

Turned off the controlled residential ventilation yesterday because it condenses directly on the facade at the supply air grille on cold nights

We have the same, IMHO it could have been solved better (I would choose a different provider for the next house).

Please first invest in some usable hygrometers (from 12 euros),

This is IMHO(!) the only sensible contribution in this thread. Just because someone says it is damp, I would not start technical drying (which is always expensive). Please measure the indoor humidity (preferably over 24 hours, before and after ventilation, etc.)! Then you can see further.

The same applies to the question of laying vinyl. A floor is ready to be covered when the measurement value is right. In case of doubt, please ask the screed layer, the site manager, or the contracting party.

From practice: The floor typically tends to slope at the edges and corners. One might consider installing skirting boards only after one year.

We have that too, IMHO it could have been solved better (I would choose a different provider for the next house).

What have you done about it? I just screwed a small sheet metal underneath and sealed it with silicone. Now I hope that the condensate drips off.

We have that too, IMHO it could have been done better (I would choose a different provider for the next house).

Which provider do you have now (or did I overlook it)?

The controlled residential ventilation system is from Pedotherm, the supplier chosen by my developer (the actual device is from Vaillant, but that has nothing to do with the described issue). In front of the fresh air inlet in DN150 there is a simple grille (weather protection grille, louver grille). I bought a plastic profile that I want to install for condensate drainage (drip edge). Unfortunately, I haven't gotten around to it yet ...

For the next house, I would make the duct slightly thicker and choose a better designed grille (larger open cross-section, drip edge for condensate) (such "weather protection hoods" do exist, but AFAIK only for DN160).