Is additional insulation of the attic sensible in new construction?

The contractor insulated the ceiling with Knauf glass wool, thickness unknown. Later, I put Climowool 160 clamp fleece plus climate membrane between the rafters. No. Everything is dry. Now my model railway is on top, it is not harmed.

How did the GU make the glass wool walkable? Which boards are on it?

No records. Boards.

Great, I think I'll do it something like that too.

Pay attention, Karsten has wooden beams as far as I know and no concrete floor slab!

I also have an uninsulated attic, and I wonder what I could store up there. For example, I wouldn’t carry my skis up there because of the heat in summer. It feels like it gets 50°C up there. I also can’t really imagine storing anything paper-related (I still have one or two boxes of books that I keep for nostalgic reasons) - because of moisture. Clothes would be the same... What’s left? I have stowed away the leftover tiles, and the Christmas decorations won’t be harmed either. What else can go up there? Am I worrying too much?