Attic damp? Condensation?

Hello everyone, we have insulated our attic with insulation and a vapor barrier foil, the general contractor normally only does a cold roof but since we did the attic conversion ourselves, we also insulated it. Additionally, the attic is equipped with a thermally insulated staircase. The heating has been running now for about 5-6 weeks and has completed the screed heating program. Yesterday, I noticed when I wanted to hang lamps in the attic that it is dripping at one spot near the chimney and that water had collected on the vapor barrier foil in 2 or 3 places. I then removed the foil at the chimney and took out the insulation. The insulation is completely saturated and only at the spot near the chimney, the foil underneath, that is the one from the roof, is also wet as are the beams of the roof structure. My site manager says it is condensation water, but I find it strange that it only occurs near the chimney. He said the chimney is near the attic staircase and this is not yet sealed, so condensate forms there. He told me to seal the staircase, which I have done, but I really can't imagine that he is right about the condensate because the attic was not really cold... what do you think about it?

The moist air could have entered the attic through the staircase opening, then passed through the vapor retarder and then condensed on the underlay membrane, which is cold. Perhaps the vapor retarder is worst connected at the chimney.

What I wonder: Do you really have a vapor retarder there, or is it a vapor barrier??? Is the space between the attic and the upper floor also insulated?

well cold roof, who calculated that for you? Where is the dew point now, how warm is it now on the roof?

Between the attic and the upper floor there is insulation, and additionally the attic itself is insulated. There is a vapor barrier. What I noticed was that the foil had come loose on one side of the house wall and was therefore not properly sealed, but that does not explain to me why it is damp specifically at the chimney.

Maybe the chimney is cold? How is it insulated? Previously the roof was cold, now warm, so condensation.

It could be coldest near the chimney. The chimney practically represents a thermal bridge. Maybe you haven't found the other wet spots yet. However, the workmanship is overall more than questionable. Do you know the SD values of your vapor retarder and roofing membrane?