Asfaboard vs Örnpapp - Vapor Permeability

[Roger G Olsson]

What is more diffusion-open, Asfaboard or Windpaper? In my case, it's about Örnpapp from ByggMax and their Asfaboard.

The Asfaboard is intended as a wind barrier inside the outer sheet metal cladding on a small shed that will then be insulated with fiberglass. The reason I'm asking is that I was planning to place the Örnpapp first, against the studs, and then place the Asfaboard on top of it. (Then I was thinking of adding air and nail battens) But if the Asfaboard is less permeable, could water vapor accumulate between it and the Örnpapp?

All advice & insights are welcome on this idea.

 

[Rickard.]

The Asfaboard has higher resistance, but it still has low sd-values, so it's doubtful if it makes any difference. Why do you want to use both?

 

[Roger G Olsson]

The Asfaboard has higher resistance but the sd-values are still low, so it's questionable if it really matters, why do you want to use both?

I read that if wind and rain lash against the metal wall, water can seep in, causing the Asfaboard to get damp sometimes. I'm thinking that if moisture does get in, even if it's only between the Asfaboard seams, it could lead to moisture in the wall's insulation.

Also, the Örnpapp has been sitting in the garage for a few years, taking up space, so it's also a way to get rid of it.

 

[Roger G Olsson]

Read that if wind and rain beat against the metal wall, water can seep in and make the asfaboard damp sometimes. Thinking that if moisture then gets in, even if it's just between the joints of the asfaboard, the insulation in the wall might get damp.

Also, the Örnpappen has been sitting in the garage for a few years taking up space, so it's also a way to get rid of it.

The shed has been finished for a long time, but I just happened to ask AI (ChatGPT) about vapor permeability. He said that both Örnpapp and, for example, Bison synthetic wind protection are more permeable than asfaboard.

 

[AndersS]

The shed has been finished for a long time, but I just happened to ask AI (ChatGPT) about vapor permeability. It said that both Örnpapp and, for example, Bison synthetic wind barrier are more permeable than Asfaboard.

And you've checked that it's correct?😎