ᐅ Insulation of Our Top Floor Ceiling

Created on: 11 Mar 2013 09:40
A
a-friend
A
a-friend
11 Mar 2013 09:40
Hello everyone,

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

The attic will not be used as living space in the future, nor for storage. At most, you might need access to the satellite dish or the chimney. There are no roof windows.

A brief description of the situation:
The roof has insulation between the rafters – you can practically see the reflective silver backing of the insulation. To provide stability to the roof insulation, wooden battens have been attached to the rafters at intervals of about 0.5 m (20 inches).

From inside the living space, the ceiling layers are as follows: drywall, double cross battens, vapor barrier, light insulation, wooden beams on the attic floor.

I now want to lay insulation boards or insulation wool on the attic floor. Is there any reason not to do this? Should I lay a foil on the floor first? In a video by Isover, it is shown that a foil is laid under the insulation wool, which must be installed airtight in the attic.

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

Thank you very much for your help.

Uwe
Musketier11 Mar 2013 11:23
Water condenses whenever cold air meets warm air.
If your floor is cold, you naturally need a vapor barrier beneath the insulation as well.
However, you already have one between the battens and the light insulation.
A
a-friend
11 Mar 2013 11:45
Hello Musketier,

That’s exactly what I’m aiming at. So you also think I could skip a second vapor barrier? That actually sounds reasonable and would simplify my plan.
I was planning to simply roll out mineral wool insulation in two layers, with the second layer laid crosswise to the first.

Best regards,
Uwe
Musketier11 Mar 2013 11:59
From a purely logical perspective, a vapor barrier in that location would not only make no sense but would actually be counterproductive, as it could lead to moisture being trapped between the insulation layers. However, this is just a layperson’s opinion.

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