Moisture in the bedroom on the exterior wall - Where does it come from?

Cold outside temperature and lack of heating = cooled-down masonry Now warm and humid air from the heated parts of the living space flows into your bedroom and condenses on the cold exterior masonry, and you already have damp walls. The area at the transition to the basement masonry is probably only particularly cold because you typically have a thermal bridge there in old buildings, which is why you notice it there first.

Solution: Either ventilate properly and/or heat the bedroom. Otherwise see

Edit: I wouldn’t be surprised if the moisture in the basement is due to the same problem.

Edit2: And no, "properly" ventilating does not mean simply leaving the bedroom window open ;-)

an exterior wall (double brick masonry) looks slightly damp at the bottom.

Or is it not a new building?

Double brick row new buildings probably only exist near the equator.

Or do you think that the lack of heating is already the reason why the wall looks damp?

Yes and no. Heating the room during the day will definitely help. At night, especially with the heating turned off, you still get enough moisture in the bedroom that condenses at places where the dew point temperature is undershot. Typically at the transition floor/wall, ceiling/wall and especially in corners or poorly ventilated areas, e.g. behind cupboards.

So 1. Heat during the day, ventilate briefly in the evening and morning, and leave the bedroom door open at night so that the moisture from the occupants does not accumulate only there.

2. A double brick row 24cm has a U-value of about 2.0 W/m²K. I am not a fan of retrofitting insulation on the exterior wall, and everything with a U-value below 1.0 I would also leave alone – but here I would strongly recommend it. Not only for energy savings, but especially for increasing comfort and reducing such phenomena.

Double brick row new buildings probably only exist near the equator

:D yes, I am not very knowledgeable about that... but that heating is necessary, I know :)

Thank you. We wanted to have the facade painted this year. Now we are considering the insulation. Wishing everyone a nice weekend.

My father-in-law doesn't heat his bedroom either. And what does he have behind the wardrobe.... :p

He could easily open a cheese dairy with the way the mold is thriving back there. Horrible. Simply too stupid to create a proper room climate.

@TE the topic of insulation and ventilation will only help you to a limited extent. Better start heating properly or the damp walls will soon be your least problem.