Insulation of our top floor ceiling

Hello everyone,

I want to insulate the top floor ceiling of our house (built in 1986).

The attic is not intended to be inhabited later, nor to be used for storing any items. At most, one should be able to access the satellite system and maybe the chimney. There are no roof windows.

Briefly about the conditions:
The roof has rafter insulation – you can practically see the silver backside of the insulation. To give stability to the roof insulation, wooden battens have been attached to the rafters at a distance of approx. 0.5 m.

From the apartment side, the layers of the ceiling look as follows: drywall, double battens crossed, vapor barrier, light insulation, wooden beams on the floor of the attic.

I now want to lay insulation boards or insulation wool on this floor. Is there anything speaking against that? Should I lay a foil on the floor again? In a video by Isover it is shown that under the insulation wool a foil is laid first, which should be installed airtight on the attic.

Or does my vapor barrier in the ceiling replace this foil?

Thank you very much for your help.

Uwe

Water condenses wherever cold air meets warm air. If your floor is cold, then of course there must also be a vapor barrier under the insulation. However, you already have that between the lathing and the light insulation.

Hello Musketier,

that's exactly what I'm talking about. So you also think I could do without a second vapor barrier? That actually sounds plausible and simplifies my plan.
I just wanted to roll out insulation wool, two layers, with the second layer rolled out offset to the first layer.

Regards
Uwe

Logically speaking, a vapor barrier in that spot would not only make no sense but would be counterproductive, as you would then have water between the insulation layers. But that is just a layman's opinion.

Since you have also insulated the roof, you do not have a pure cold roof. The question is how the temperature conditions will develop in the attic.