Adding to this post, only because its a good one to keep up to date,. R- insulation value is always the sell (factor) in purchased kit builds. I say, regardless of the R value, HVAC will be needed for most parts, if for nothing more than removing moisture, and adding some comfort.. the fact is for interior walls? if the beams or logs or whatever is used, is not dried, then there is an appropriate shrink factor based on moisture content, and size to allow for shrinkage on interior walls. other wise doors and other interior factors come into play.. around here it's been 1-1/2" for interior walls. These are not connected to the ceilings, something to think about when building green, or sawn from the woodlot,,