I'm guessing these are solid logs?
i live in a very old house. a portion of which is log walled construction
If that's the case wood has an R value of about 1 per inch of depth .... so with a solid log around 6 inches diameter you have have a little better than R7.
If the logs are stacked horizontally the weak point will be the chinking. If it's weak it may be drafty.
Applying rigid foam around the perimeter will help some though there will still be cold migration from the ground under the slab. The ground frost will likely penetrate the soil deeper than you will be placing the insulation.
my question, would i be better off trenching along the north wall and inserting board insulation to break contact with the soil that freezes and never receives any sun during winter months or digging down several inches and doing a ground cover with board insulation? my theory is that by breaking the slabs contact with the frozen soil i will use the ambient soil temperature to my benefit
So ... you would need to dig the entire area around the slab deeper than the ground frost line and place the rigid insulation the entire depth to prevent the frost getting under the slab.
You might consider applying rigid foam insulation directly to the slab inside then cover with plywood as a subfloor .... this will provide a thermo break from the cold slab. There is also the consideration of adding in-floor radiant heat.
Just a thought.
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