Isolate wooden staircase; vapor sense?

[logredudon]

Hello,

I have a wooden staircase to climb from the ground floor to the attic.
The lower part of this staircase is in the basement. I want to isolate it with rockwool (7,5cm) + placo.

But which side should I put the vapor barrier on? Against the stairs or against the placo?

Goods.

[Christophe]

I did'nt understand everything.

A little diagram will help us to help you ...

[aerialcastor]

I did not understand everything either, but the vapor barrier always gets hot.

[logredudon]

I specify: the glass wool will be under a wooden staircase. The top of the steps is in the house (on the ground floor) and the bottom in the basement.
So the vapor barrier, stairs side or basement side?

[moby25]

Hot side, so staircase side

[logredudon]

Thank you!