Cob RE: "insulation," etc.

[John Schinnerer]

Aloha,

-----Original Message-----
From:	shonlenzo at juno.com [SMTP:shonlenzo at juno.com]
>I have heard that cob only has an R value (insualation) of .25 per inch of 
cob.
>Is this true-The heat would be sucked right out -"Stone cold"

The first thing to be aware of is that Cob is a thermal mass material, not an 
insulating material.  With all known building materials, there is a trade-off 
between insulative values and thermal mass.  More mass typically means less 
insulating, and vice versa.  If one tries to argue the value of cob from the 
standpoint of insulation, one has already lost the argument.

According to physics, heat "flows" from one place to another in three ways: 
 conduction (flow of heat from molecule to molecule within the material 
itself), convection (flow of heat to (or from) the air (or water, other 
surrounding medium, etc.)) and radiation (flow of heat from source to sink 
via "radiation" - without messy physics explanations, this is why the sun 
warms your skin even when the air is freezing and why you're colder at night 
under the open sky than under trees).

R-value is a measure of NOTHING other than resistance of a material to 
CONDUCTIVE heat flow.  It says nothing about the effect of the material 
relative to convection and radiation.  It also says nothing about the effects 
of thermal mass (or lack thereof).  And since Ianto isn't on this list to say 
it, I'll say it for him - R-value is also a product of the commercial 
insulation manufacturing industry.  They have made it the be-all and end-all, 
to the point that codes refer only to R-values and have no appropriate way to 
account for thermal mass materials and reflective materials.

It turns out that in most typical dwellings, far more heat is lost by 
convection and radiation than by conduction - but "insulation" as the 
building industry knows it only prevents loss by conduction.

I'll quit for now...does anyone know of a good FAQ on the above topics 
(thermal mass, physics of heat flow, etc. applied to building materials)?  It 
would be a good resource to point to when these sorts of questions come up. 
 If there's not one out there somewhere, let's write one!

John Schinnerer