Humidity permanently too high, mold formation, cause?

Place the wardrobe and bed preferably against interior walls,
and never against exterior walls without ventilation behind.
Do you sleep with the heating off and the window closed, are the windows fogged up in the morning?
Is the heating installed as underfloor heating or radiators?
We also have a lightweight expanded clay bungalow, without mold.

The wardrobe is against an interior wall. The bed with the head towards the exterior wall. It is not possible otherwise. There is a window on one exterior wall, nothing can be placed there, and the bed is on the other one. You could swap bed and wardrobe but that doesn’t make it better.

We have the heating off at night. During the day actually off as well, now I just heat during the day and ventilate repeatedly to get the moisture out.
Now the window is closed at night; in summer it is also open at night if the temperatures are suitable.
If it is cold outside, water also condenses on the window.

No underfloor heating, just regular wall-mounted radiators installed.

I aired out the bedroom this morning after getting up, then turned on the heating. There were 69% humidity just now, after 10 minutes of airing it went down to 45%. Window closed again, heating on.

I aired out the office from 60% to 42% in ten minutes.

Let's see how long it stays like this, or how quickly it rises again.

Let's see how long it stays like this, or how quickly it rises again.

Then ventilate like this every day, in the walls, furniture, things, etc., it takes 2 weeks for the moisture to come out. When sleeping with closed windows, heat so that the windows no longer steam up. Or sleep with an open window, we do that, with thick 4-season blankets, one already with a winter blanket and one still with an autumn blanket.

That is a manageable period of time.

Now airing out works better too, sunny high-pressure weather. Last week it was always quite mild but wet outside.

I am fine with sleeping with open windows, but I can’t get my wife to agree.

But doesn’t it get damp inside then as well, if it’s not really cold? So with over 0 degrees and damp-cold weather, moisture should get in then, right?

So, I have now gotten myself a moisture meter without pins, so just to place it on and read off (Mestek WIM700A).

Depending on the wall (interior or exterior) and the use of the room, values between 20 and well over 60% moisture in the wall result. So in my opinion, this does not initially indicate any water ingress.

Even in the bedroom behind the nightstand (where there was mold) the values were in the yellow range.

But two things make me suspicious:

When I measure in the bathroom in the shower (tiled interior wall), the device immediately jumps to 100%. Does this now indicate a leak or is it caused by water coming through the grout during showering? On the other side of the wall, no unusual values are measured.

And when I measure the floor in the bathroom (tiles, no basement underneath), I also get values of 80-100%. In the hallway (tiled) the values are sometimes in the 70s as well, but that is still the yellow range.

The humidity in the house is also not as high now. So with closed windows, it rises to 60, but when you then ventilate, it calms down again at first.
Only in the bedroom are there still values around 80% in the morning, which you then ventilate away, but of course I would prefer it not to go that high at all.

Only in the bedroom are there still values around 80% in the morning, which are then ventilated away, but of course I would prefer if it didn't get that high at all.

Therefore, I have advised a decentralized ventilation!

If you only have the problem in the bedroom, then you can have a decentralized ventilation installed.
And yes, while you sleep, moisture enters the room. An adult exhales about 1 1/2 liters during a sleep phase, according to my knowledge. You counteract that with manual ventilation (daily shock ventilation) or automatic ventilation.