Attic damp? Condensation?

Actually, it was warm in the attic so far because it was insulated, but after I removed the insulation at the chimney, it has become colder. So it was warm in the house before and also warm in the attic, therefore no condensation should have formed, right?? The chimney itself is not insulated; it is simply built up high. Part of it is in the insulated area and part under the foil in the exterior area, the chimney goes through, but it is sealed with the foil. Is your chimney insulated? Honestly, I have never seen that...

The condensate forms on the underside of your roofing membrane. This is basically the first cold point, also known as the dew point. Whether your attic is heated does not play a role. In the chimney area, condensate can also form because it is cooler there. As mentioned, maybe this is just the only spot you have found so far. I tend to think that your entire construction is wrong. Any entry of moisture into your roof insulation layer should probably be prevented. This can only be done with a vapor barrier that is properly sealed everywhere.

If you have not installed a vapor barrier, you should at least know the SD values in relation.

So we installed this vapor control membrane..Isover Vario KM climate membrane. This was sold to us by the building materials supplier.

I am not an expert, but according to my research, it is not necessarily required to install a vapor barrier in the attic.