Log cabin walls

Tom,
I have been reading and enjoying the advice in your column along with
Professor Hill's remarks.
We live in a log cabin in Aroostook County, expanded and winterized in
2003. The original Ward Cabin (20 by 30 feet) has their short, camp grade
log walls. I have caulked every log joint on all but the south side. The
rest of the construction (basement living space and a two story el bringing
the total to a bit less than 1500 square feet) is stick built with 6 inch
insulation in the walls. Roof insulation is over 12 inches of fiberglass
with no room for more without blocking gable vents. Under the floors above
the crawl space, I added to the foil- backed reflective paper, bubble wrap
insulation with foil on both sides. Windows are Anderson low E, mostly
double hung, with one Anderson architectural and 3 Anderson awnings. Heat
is oil fired radiant in all floors, up and down. We also run an Ashley
wood heater in the living area whenever it is cold (less than 2 cords last
year). We have pretty consistently used about 550 gallons of oil per year
(temp set at 60 degrees all the time), before and after we moved in full
time
Questions:
1) Is there anything else I can do to the log walls, without radically
changing the inside or outside looks, to make some additional gain in heat
retention?
2) If we go away for 2 to 3 months in the winter and shut down the
furnace, how cold might our crawl space get without heat (Note that there
is very little concrete exposed above ground. Though we are set into a
hill, we have a northern exposure)?
3) In your July 5 column you said insulate with anything but "No bubble
wrap." Why?
4) Any additional suggestions for the situation I have described?
5) For a home with our square footage, what is the best fuel
consumption I could hope to achieve?
Thanks,
Michael

Hi Michael,
Log cabins are difficult. One way to bump up the insulation of log cabin
walls is to insulate on the inside and then cover with "V" match pine. That
loses the thermal mass which is of value. The ideal way is to cover the
outside with log siding, and foam, but that is an aesthetic compromise that
I would not want to make!
If you go away and leave the heat off, the crawl space won't freeze, but
there is a strong possibility of some condensation damage from moisture
condensing on the bottom side of the subfloor.
Bubble wrap is not a very effective insulation. When you consider its cost,
it is dreadfully expensive for the amount of insulation it affords you. For
years, most manufacturers have outright lied and tried to confuse people as
to the actual effectiveness of their products. Only recently have they
started to actually claim what the actual insulation value is. That
information is usually buried somewhere on their websites.
There are some places where it might be helpful, but generally it is too
expensive compared to other more traditional materials.
I think you might benefit from a home energy audit, to try to find those
areas that might simply be treated. One area that might be enhanced is the
crawlspace walls should be insulated. Also, cover the crawlspace floor with
plastic.
Tom