Cob: RE: insulation/thermal mass

[John Schinnerer]

Aloha,

-----Original Message-----
From: W [mailto:uwu at angelfire.com]

>Poor Insulator?
>uh oh.  I was under the impression that cob was second only to straw bale
in insulative >properties.  (with cob walls being the same 16-20 inches
thickness of bales)?

Different materials - different physics.  Straw is an insulative material -
resists flow of heat/cold through it.  Earth is not nearly as insulative -
heat/cold flows through it much more easily.  

Earth is a thermal mass material - absorbs and releases ("stores")
temperature differences slowly and can store "a lot."  Straw is not much of
a thermal mass material - absorbs/releases temperature differences quickly,
can only store "a little."

So if it's cold out...it will take a while to heat up the mass of an earthen
building, but then it will hold and slowly release that warmth when the heat
source is removed.  A straw bale building will heat up quickly - that is,
the air inside will heat up quickly - but when the heat source is removed,
it will cool down quickly too.

John Schinnerer