Vapor barrier

[Guybrush666]

The walls consist of:

Wood paneling
50 mm mineral wool boards with pspp layer
Frame structure
120 mm mineral wool boards
Plastic foil
13 mm gypsum.

How important is the vapor barrier in this construction?

When I read about the dew point, it seems that theoretically no vapor barrier is needed here? (since the dew point theoretically occurs 200mm into the insulation.)

 

[useless]

The dew point occurs somewhere between the outside and inside of the wall. Exactly how far in depends on the thickness.

 

[Guybrush666]

So can I throw this information below in the trash?

https://gds.se/spara-energi/isolering/aldrig-mer-osaker-paa-aangsparren

What does dew point mean?
The dew point is when the warm, humid indoor air is cooled sufficiently to convert it into condensation.

Theoretically, this occurs approximately 200 mm out into the insulation material. If you have less than 200 mm of insulation, the indoor air will typically condense on the other side of the insulation and then it is simply ventilated away.

But if you have more than 200 mm of insulation, the condensation occurs inside the insulation.

 

[useless]

In the wall, you have a so-called temperature gradient where the temperature goes from the inside temperature to the outside temperature as you move further out in the wall. Somewhere along the way, the temperature is such that the relative humidity becomes 100% with the moisture content present in the indoor air. It has nothing to do with any 200 mm.

Then one can generalize and say that with thin insulation, it is (usually) not a problem.