Check with your local building inspector. He/She will have the latest figures on the r-value of log diameters. Washington State has done some extensive figurging and calculations to obtain these values. Check with the local light company for electricial use in this structure and compare to others in the same area of stick built. Check the logs for severe checking and dryness. How much have they settled? Pick a windy day and stand next to a wall and light a cigarette or punk if you dont smoke and look for drafts. Check the windows for breezes coming through. Again what area and who built it. Check with your local insurance agent for any records of these builders and previous claims. Good luck.