Attic problem. High humidity - Controlled residential ventilation?

You can also store all sorts of things in a cold roof, that used to be done all the time. Chairs won't break, dishes, vases, ladders, tools, solvents, and much more. Only everything made of fabric would become damp, possibly moldy, water-based paints would freeze. Cold is not a problem, it just needs to be ventilated. Churches were unheated for centuries and yet organs, paintings, sculptures did not suffer. Much more problematic can be the heat that is under such roofs in summer.

Approximately 10L have been extracted in the meantime

So far, I have extracted about 40L of water from the attic. The dehumidifier only runs during the day. From 8 p.m. onwards, it is switched off via the socket. In the mornings, my relative humidity is now below 70%. I have the impression that there was still a huge amount of water from the screed drying trapped in the wood.

During the plastering, the hatch was not covered at all, and during the screed there was a drywall panel placed on top. From autumn until the installation of the staircase shortly before moving in, the hole was basically always open. You can now clearly see how the entire rough-sawn board moves and shrinks. I had never noticed noticeable gaps before. The rest of the plaster was also nicely homogeneous, which is now changing.

Every year again 80% in the attic. The window rebate ventilators have brought nothing. I have now ordered a dehumidifier again. The good thing is that I have the ventilation upstairs and therefore also a condensate drain. The dehumidifier is simply connected to it via a drain hose.

I am considering installing a Bayern ventilator in the next few years.

We built two years ago (solid with concrete ceilings).

Basically, the best option for the cheapest possible storage space in the attic is if I don't insulate and sheath the roof and only insulate the concrete ceiling underneath, right? That's how we did it.

I have actually never set up a hygrometer because currently nothing is stored except leftover things from the house construction (tiles, roller shutter slats, floors, etc.) :D

This way, there is always fresh air through the roof ventilation and no impact on the rooms below due to the insulation on the underlying ceiling, right?

I would also like to move some things from my basement to the attic (snowboard/skis, inline skates, and a few airtight sealed boxes). That shouldn't really be a problem, right?