[Cob] cob vs.adobe R values

[Shannon Dealy]

On Tue, 20 Jul 2010, Monica wrote:

> Now I'm confused.  Why would the "worst" cob (low straw content) have, 
> or start at, a lower R value than adobe (.35 vs. .38)?  Perhaps you were 
> estimating on the cob, or does this instead have something to do with 
> the thermal mass thing?  (ie, the straw waters down the thermal mass 
> qualities of the cob).  My confusion is because i was always under the 
> impression that thermal mass isn't a factor used in computing R values.

The cob value is just a rough approximation based on the adobe value.  The 
adobe value while it comes from a standard reference is also going to be 
an approximation due to variations between adobes.  The range I listed 
was simply allowing for the wide variation of possible materials in the 
estimate, and the fact that cob will normally be lower density than adobe.

Thermal mass is not supposed to be a factor in R-value, however, failure 
to properly account for it in testing and computations has resulted in 
erroneous values being given for a number of materials over the years.

FWIW.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
Phone: (800) 467-5820 |          - Natural Building Instruction -
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