Very wet and moldy garage

I have a garage with a flat roof, I don’t know if that is relevant or not. But the following: every winter the ceiling of the garage is moldy, and the floor is completely wet, and on the walls there are damp spots about 20 cm high from the floor. Can you tell me where this could come from? P.S. 8 days ago I aired it out and the floor was dry, and now here’s the thing: I parked my car (the car was absolutely dry, so it’s not the problem that the car was wet when parked) in the garage 7 days ago and do you know how it looks now? WET wet wet. And the floor is wet again too. Why is that? Does the moisture come from underneath through the floor? Or is it because of the flat roof? Since there is mold on the ceiling above. But why on the floor then? OR do I have multiple causes? Please help me. What is the cause and what can I do? Thank you.

Hmm... hard to say since the mold is on the roof but the floor is wet.... strange. I'll talk to someone who knows about this, maybe then I can answer the question.

Regards Paul

Hello,

.... Is the moisture coming from below through the floor? Or is it due to the flat roof? Since there is mold on the ceiling above. But why on the floor then. OR do I have multiple causes of the problem?

To answer this question seriously, I would need a crystal ball ;)

Spontaneously, two possible sources of error come to mind. On the one hand, a poorly sealed flat roof – is the bitumen membrane still intact or is the surrounding zinc sheet cover (parapet cap) pulled far enough over the softwood resting on the exterior walls for the flat roof? On the other hand, the required insulation against rising moisture under and above the first row of stones may have been "saved" on when constructing the garage; both are of course possible.

To carry out precise cause research here, you should either contact the then responsible construction manager or consult an expert on building moisture.

Kind regards