ᐅ Black mold on window frames and rust on hardware

Hello everyone,

During an inspection of a property built in 2004, I noticed fairly pronounced (suspected) mold growth inside the opened window frames (difficult to describe, see pictures), as well as significant corrosion on some of the fittings.

I have never seen anything like this in our apartment, which is about 20 years older. Should this raise concerns? What could it indicate?

Many thanks!

I could imagine that moist indoor air is constantly escaping through the (closed) window and condensing inside the frame. Perhaps the window is not airtight or is never fully closed.

I also don’t see any seals on the frame. My windows have seals both in the frame and in the sash. Hopefully, they were not removed here for "permanent ventilation."

Are there trickle vents in the window rebate?

No, there are no window rebate vents. It was a child's bedroom, so definitely no planned continuous ventilation. This applies to windows on both the front and back sides of the house, not just the weather-exposed side.

Before opening a new thread, I’ll write here instead, as the title seems appropriate: with the current subzero outside temperatures, we have condensation inside the window frame on the upper floor (not at all on the ground floor!) in our new build (KfW40 standard…). This occurs every morning after opening the sash, all around/above, below, left, and right (photo). However, the interior glass panes never show condensation – the controlled mechanical ventilation system seems to effectively manage moisture from the inside. But why is the condensation inside the window frame? Could this indicate insufficient sealing towards the exterior? Unfortunately, there are already signs of mold forming. We also ventilate the bedrooms and wet rooms additionally with shock ventilation. (It shouldn’t be due to the fly screens – the condensation occurs on all upper floor windows, including those without fly screens.)
Best regards