[Cob] Hybrid Strawbale/Cob

[paul]

----- Original Message ----- 
From: "Damon Howell" <dhowell at pickensprogress.com>
To: <coblist at deatech.com>
Sent: Tuesday, February 20, 2007 12:43 PM
Subject: [Cob] Hybrid Strawbale/Cob


> Hello,
>      SInce the north side of the building never gets sun, would it  be a 
> good idea to construct the northern wall with strawbale because  of it's 
> superior insulation value over cob? I was planning to install  a wood 
> burning stove next to the northern wall too. Will strawbale be  the best 
> option, or should I just go cob all the way?

I only know from reading, not experience, Damon, but if you're looking to 
use the walls as collectors of heat then you should use cob or other mass 
all around.  Outside the walls if you can insulate during winter only, say, 
by stacking straw bales and keeping them dry, that's the best of the mass 
and R value world's together.

Of course, that assumes that you are designing it to collect direct sun from 
the south, etc.


>Another  question; I've heard cob has a heat transfer rate of about 1 inch 
>per  hour. What about the heat transfer rate of a strawbale wall?

Straw is a much better insulator than cob so it has to move heat much more 
slowly.  I think you have to separate out the idea of mass versus insulation 
and treat them as separate issues, though.  They do different jobs and can 
cancel each other out in a bad design.  One of the best tutorials on this 
can be found here http://www.thenaturalhome.com/passivesolar.html .  Don't 
worry  that they use cement for the thermal mass in this tutorial.  Cob or 
other massive walls will do it too; the principals of heat storage and 
transfer are the same.  The only thing that changes is that you have to know 
how thick to make the cob walls to achieve the same performance as the 
cement blocks.

If you get a chance let us know what you think of the principals of the 
thermal mass facts this guy teaches.  It sounds really impressive.  I'd just 
substitute cob or adobe and be done with it.  I'd insulate on the outside in 
winter with straw bales, and I think the use of the wood stove would be near 
nothing.

p