New construction - mold on the roof beams

Underlay membrane - ventilation element
that's what those things are called

Thank you, that would have already solved the mystery :)

they should be installed at the latest when water droplets regularly hang on the [Unterspannbahn]

they should go in at the latest when water drops regularly hang on the underlay membrane

For what reason should water drops regularly hang on the underlay membrane? With a cold roof, that should or must never happen...

then there is a construction defect or a leak in the thermal envelope in a cold roof (it can be the attic ladder or penetrations or or), if more warm air comes from below than is ventilated away at the top, the underlay membrane is damp or wet. we touch the underlay membrane every time we are upstairs, everything is dry with us, and there is always a draft to be felt.

I think that is no longer a problem, the water droplets are becoming fewer and fewer. The question is just what to do with the roof beams, is it enough to treat them?