Insulation between rafters in the uninhabited attic

Hello everyone,

Last year we built a new house or had our house built. The house has a gable roof, and the top floor ceiling is of course insulated. The attic above, with a height of 1.6m, is uninsulated. Because of the height and the lack of windows, this attic will never be inhabited. However, it is our only proper storage space since we have no other storage rooms or anything similar. So everything that we do not need permanently downstairs will be moved upstairs.

I have now asked myself whether it could be of any benefit for the stored items if I install insulation between the rafters. My theory was that especially in winter it might not get quite so cold up there, which could perhaps protect our "things." On the other hand, in summer of course there is the blazing heat up there and no chance to get it out.

Insulating with mineral wool and screwing on OSB boards costs roughly 1000 euros.

What do you think about such a measure? Completely pointless? Maybe still useful?

Please help me out, because it’s not like there aren’t other projects where the money would be well invested... What do you think?

Best regards and happy holidays!
Kind regards

Ps: just to emphasize it again. It's not about whether it will pay off in x years. It won't because the ceiling is already so well insulated. For me, the question is whether it makes sense to install insulation in the attic solely as a storage space, considering the temperatures and/or humidity. If yes, what would you recommend?

I had a very similar plan, only that with me the insulation is done on the intermediate rafters first:
https://www.hausbau-forum.de/threads/zusätzliche-Dämmung-des-dachbodens-im-Neubau-sinnvoll.32760/

showed a pretty good solution.

However, I now also have some concerns about this, because if moisture rises from the living space to the then semi-cold attic, mold could possibly form there. The attic hatch must be *very* airtight, or you must ensure ventilation of the insulated cold attic.

The attic should ideally have a Velux, like ours. Then it gets ventilated. No problem with mold. And the door, for us it's a door to the floor with stairs, not a hatch, it's a double-glazed PVC patio door. It's airtight. So, pay attention to the surroundings, then it will work.

Yes, I have read your topic, but your starting point was that the roof was insulated (or was supposed to be) and you wanted to know if it might be financially worthwhile to do it differently!?

No, in our case there is actually no hatch or window at all. Only at the ridge at the top the Delta foil (I think that's what it's called) is folded over. If you reach in there with your hand, you can practically touch the uppermost tiles. So the air can escape there.

... So as long as this ventilation is maintained, which can also be ensured with insulation, there is nothing against it?

Would you do it the same way if it were the only storage room?