Additional insulation between the upper floor ceiling and the attic

Hello,

I currently have a cold roof with a crawl space :D and would like to lay tongue and groove boards as flooring to simply store unimportant things like tiles, roof tiles, etc. there.

Currently, the insulation consists of drywall ceiling upper floor -> vapor barrier -> mineral wool. So when I'm in the attic, I basically look at the wool between the rafters.

Now I still have plenty of styrofoam insulation boards left over and wonder if it makes sense to work them in between the mineral wool and the tongue and groove floor. Surely I would have to compress the wool a bit for that. So it would be ceiling upper floor -> vapor barrier -> mineral wool -> styrofoam -> tongue and groove.

Does that even make sense or better just ceiling upper floor -> vapor barrier -> mineral wool -> tongue and groove?

I hope I didn't describe it too badly and I would be very happy about some good advice.

Thanks!

No, it doesn't make sense. Compressed mineral wool leads to worse insulation. And to condensation in the mineral wool.
So do not install the [Rauspund] in a way that it fully contacts the mineral wool. If the rafters are not high enough, you have to add layers there. Air must be able to pass between the [Rauspund] and mineral wool to carry away moisture.
All you can do is insulate the roof itself further if you still have enough space.

Ah ok, thanks for the answer. Currently, there is about 3 cm of air space in between, is that enough? At the moment, there is no insulation in the roof slopes, only a kind of gray thick foil or fabric membrane (I’m not exactly sure how to describe it) with ventilation openings. I thought you would have to install some sort of vapor barrier there before insulating?

Or is a layer of air sufficient and then the polystyrene insulation? So basically from outside to inside: roof tiles -> this fabric membrane -> air -> polystyrene and, if desired, cladding, or does mineral wool have to be used instead of polystyrene, I also have some left over?

Many thanks for the information!

I'll jump in here...
Our roof is being redone and the insulation improved. In the process, the old insulation will be removed. Between the upper floor and the attic (occupied), insulation will also be installed again, and I would like to know whether a vapor barrier must necessarily be installed here? The thermal envelope will be insulated again.