Attic Insulation: Optimization Potential in Current Insulation

Hi everyone,

I bought my first home 6 months ago and now we are looking at what needs to be done. We noticed that it is very cold in the attic (about 2-5 degrees warmer than the outside temperature, but 10-15 degrees colder than the indoor temperature).

It seems to be insulated on the sides with 13-20 cm of glass wool (depending on where you measure / how much it is compressed), but in a few places it has been missed / fallen down. From your experience, how much % heating cost can I save / what makes sense to do?

a) Only seal the leaking spots
b) Add another 10-15 cm on top
c) Different material (although according to the internet, stone wool etc. isn't much denser)
d) Something I haven't considered yet? (stone walls, floor)

Honestly, it looks a bit like there were moisture problems there? It looks like water stains. Perhaps the insulation was removed because of that?

The insulation should also not be compressed too much and the foil should actually be sealed airtight. It definitely should not be like this. As long as everything stays dry, I wouldn’t worry. However, I would actively monitor it and check if moisture still occurs there. Depending on the foil, the glass wool should have a certain distance so that the glass wool has ventilation and can dry out.