[Cob] Lava Cob - defeats the purpose of thermal mass

[Ocean Liff-Anderson]

Pardon me for interjecting a critique into the controversy here. But  
as Ianto taught me and countless other cob builders, a major benefit  
of cob vs strawbale construction is the incredible thermal mass of  
the material.  By creating 24" thick solid walls, we add a thermal  
"battery" to our buildings which absorb and release heat gradually,  
creating a stable thermal environment similar to a cave.  So the  
addition of pumice - which may increase the insulative quality of the  
material by trapping air - would unfortunately also prevent the  
material from acting as thermal mass.

I am again compelled to repeat a past observation of dialog on the  
Coblist: many instances of novice speculation on the cob listserv,  
not grounded in the experience of the material of cob, which has a  
tradition passed down from the middle ages.  Why do you want to  
change the nature of a building material which has served to create  
cozy homes continuously inhabited for over 500 years on the chilly  
coastal shores of Devon, Wales?  Why question the long established  
experience of great-great-grandparent builders?

Novelty and innovation do not always represent improvement.



On Jul 18, 2011, at 11:43 PM, Janet Standeford wrote:

> Are you saying theirs is true R value?
>
> As for the energy model I know of, it passes muster with building  
> officials as R value for my house.
>
> The point I am making is that .5 for regular cob is a pretty low  
> guess on their part versus the nearly "1" I will be getting. So it  
> doesn't appear that the pumice actually adds anything to the  
> equation when theirs comes out to "1" with the pumice.
>
> Also Shannon, effective value or not, it was measured at 19 for 20  
> inches. Yes, site, sun, etc have everything to do  with it but as  
> cob will never have a true R value due to variances in the mix and  
> soil, effective value is the closest thing we will ever get to  
> measuring it.
>
> So don't jump down my throat for going with what I can get in the  
> way of a measurement just because I have an opinion on regular cob  
> versus pumice cob and the claim made on their website regarding R  
> value for regular cob!
>
>
>> As I have explained previously, cob is NOT anywhere close to R19  
>> for 20 inches, your energy model is specific to your building and  
>> site.  I believe the term used on your paperwork was "effective R- 
>> value" it is not a generic design definition that can be used for  
>> other cob installations. Effective R-value has a specific context  
>> and is only meaningful in that context, it cannot be applied to  
>> other buildings unless they have a similar design, latitude, sun- 
>> hours per day, and probably other conditions.
>>
>> Shannon C. Dealy      |               DeaTech Research Inc.
>> dealy at deatech.com     |          - Custom Software Development -
>> Phone: (800) 467-5820 |          - Natural Building Instruction -
>>    or: (541) 929-4089 |                  www.deatech.com
>>
>
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