Internally insulation log cabin - condensation

[HarryC89]

I'm actually in Sweden but I'm a brit so thought I'd try on this forum.

We have an old (150 yr old) log cabin which I am renovating, currently insulating the upstairs. 2 x 4 stud walls with 100mm celotex between studs, VCL, then 50mm Celotex over studs.

The walls are very uneven so there is a cavity of varying thickness ( 10 - 50mm) between the external face of the insulation and the internal face of the log wall. I'm concerned about condensation forming there. Should I ventilate the cavity, and if so to what extent?

I have fit soffit vents so ventilating the wall space along the eaves would be simple but I don't know what to do about the gable wall space and how much to ventilate it by, if any.

Any help massively appreciated as I'm basically done with the insulation between the studs and need to move on to the next stage.

 

[HarryC89]

I forgot to add, below the space there is no kitchen / bathroom (different part of the house which is timber frame). Wood burning stove downstairs so the air is pretty dry over colder months. There is a large square opening in picture 2 currently jammed with mineral wool (hole for a hay hitch) which I could open and put a vent over.

 

[HarryC89]

oops , ignore this.