Additional insulation with west coast boards?

[Osek]

I have a summer house from '63 that has been remodeled a bit over time. Most of the house still has its old dimensions on the exterior walls which are very thin. Obviously, this is a bit of a problem during colder months and when the wind blows strongly against these exterior walls, you can almost feel the draft 😂

I was thinking of looking into a simple additional insulation or alternatively putting in västkuskivor in the sections?
When I opened it up to see what's behind the outer panel, I see this black/gray board which I guess is some form of asphalt board?



Everything is bone dry but as mentioned, it could use a bit more insulation. Your tips and suggestions for a smart choice of insulation and a way forward/technique would be appreciated.

Thanks.

 

[TheGame]

West Coast board You can place it, but you should not place it in the compartments, instead over the studs so it creates a sealed wall without thermal bridges.
Then you nail battens over the West Coast board and then the panel.

 

[Osek]

Västkustskiva You can set it, but you should not set it in the compartments, just over the studs so you get a sealed wall without thermal bridges.
Then you nail battens over the Västkustskiva and then the panel.

Ok, I'm thinking more now afterward to tear down the battens and put the boards directly against the asphalt board, and then on with battens?

 

[TheGame]

Ok, was thinking more now in retrospect to tear down the battens and put the boards directly against the asfaltsboarde then on with battens?

Yes, the west coast board should be placed against the windbreak, which in this case is the asfaboard 👍