[Cob] Covering log home with cob

[Monica Proulx]

To Jen in Austin

Just some thoughts regarding your letter about covering log with cob.  I am
by no means an expert on either cob or log.  That said, I agree with Mr.
DuPont that there may be a termite problem created by combining log with
cob. (I know they are a big problem in Louisiana, what about Texas?)  It
would seem you will be providing "cover" for termites to tunnel right to
your logs without even having to build their own "cob" tunnels (termites
don't tolerate open air well, it seems).  I have always heard one never
should pile dirt next to wood for this reason.

Also, you may want to check out the following website about a study done in
early 1980's by the National Bureau of Standards (U.S. govt. entity in D.C.)
about the value of the thermal mass of log (it does have some).  It was
impressive when I read it 15 years ago, and fortunately it is now on the
internet today.  It compared the cost of heating two identical 20 ft. sq.
structures that only differed in their outer wall make-up; one had 7 in.
thick (squared off) log walls of R-10 insulation value, the other had
standard stick built fiberglass insulated walls (with a greater R-12
insulation value).  The log structure used 46% less energy to heat and 24%
less energy to cool.  Which might lead one to wonder why would one want to
tamper with that?  So apparently log is a unique combo of insulative and
thermal mass factors.  Maybe the insulative value of the log would work
against the thermal mass effect of the cob.

Perhaps the outer cob wall on the south side as Joe mentioned is the best
way to marry the two together, as in cob wall with windows facing south,
with some space between the cob and log walls(perhaps enough for a narrow
porch type thing). Then on late afternoons of sunny days one could open the
log wall windows harvest the heat stored in the space between cob and log,
maybe facilitating the air flow with "return vents" under the log windows.
Not a trombe wall surely, but maybe it would work somehow. Better still, if
you have room put a low trombe wall of cob,  short one, on the south side
inside your log home where sun can hit it and store heat. Having lived in a
modern passive thermal home for years I can tell you that if it is done
right, you might have some heat to spare.  In fall and spring we had to
regularly dump heat through open windows, ours worked so well.  I think the
whole idea of passive thermal heating and trombe walls in particular, are
underutilized enormously.

Or how about a green house room attached to the south side?  That is the
best of both. As much as I love log, today I myself wouldn't consider
building a whole building out of new log as it seems a waste, but this has
already been done "for you" by someone else.  Re-using and enhancing energy
efficient buildings is a good thing. There are ways to chink logs that make
them more energy efficient, by the way.

http://www.oldvaloghomes.com/EnergyEfficiency/energy_effieciency_of_log_homes.htm

Good luck,
Monica


copy of letter:

"We're thinking of buying a stripped bare log home and
slathering the inside and outside of it with cob.  is
that crazy?  We'f like to install solar power and
rainwater collection as well.  We not only desire a
cob home, but we are thinking it would be a terrific
way to help insulate the home (no a/c, wood-burning
stove, etc.)  What are your thoughts?"
Thanks!
Jen in Austin, TX