Mold in the basement: moisture from below or condensation problem

Hello everyone,

I had to find out yesterday that a mold problem has developed in my basement, see photo.

The wall is an exterior wall in a heated basement room that I use daily. In terms of height, the area of the baseboard is about 1.5m below ground level. In front of the baseboard, there was a cupboard and moving boxes close together, so almost no air exchange, even though the room has large windows (mostly closed).

I haven't had the time yet to clear the area further, but I am concerned about whether the problem was caused more by water coming from below or by water that condensed on the cold exterior wall? It looks like water from below, but on the other exterior wall of the room, there is nothing to see, but this wall was not blocked either. Also, there should be no water accumulating outside the house, as the slope leads away from the house and above the area is a terrace, which also initially lets the water flow away.

How can I best find out where the mold problem comes from, that is, what should I pay attention to when clearing? Do you have any tips?

Thank you very much Tassimat

New building, poorly ventilated, wall obstructed. Room often used but rarely ventilated. So I would first not think outside or downward, but of "misuse."

Or are there indications of damp walls, floors?

New building, poorly ventilated, wall blocked. Room often used but little ventilated. So I would first not think outward or downward, but rather of "misuse." Or are there indications of damp walls, floors?

I have to clearly disagree. Such damage does not come from misuse. Something is wrong with the sealing or insulation. Measure moisture in the wall and temperature. Then see where it comes from.

In any case, measure as suggested by and exclude ingress from outside. In new buildings, basements take particularly long to dry, so as suspected by , mold can quickly develop in unventilated spots. I tend to think that there is a ventilation/dew point problem behind the cupboard / behind the boxes. How and where is the room heated?

It is not a new building, but a renovated house from the 60s. The basement walls are not insulated. On the opposite side of the room, there is a radiator about 4m away from the mold.

"Misuse" would be preferable to me at first, rather than a leaking basement. Well... excavating outside would still be possible, but I am still hesitant about the effort. However, it might actually be quite sensible, because then I could waterproof and insulate. This is my study, and I prefer it to be rather warm. Insulation would certainly make sense energetically.

Okay, if it is not a new building and an uninsulated wall, then it is very likely a ventilation issue. But even there, of course, external insulation would help massively.