[Cob] straw - in cob - does not insulate!

[Ocean Liff-Anderson]

the straw fibers which are embedded in a cob wall are compressed to  
such a degree that it doesn't trap a significant amount of air to  
serve any insulative function. cob structures are cozy because of  
their thermal mass - not insulation - in their ability to store heat  
and stabilize interior temperatures, much like a cave dwelling.

so, let's be clear on the coblist:  the tensile strength from the  
fibers of straw is what make cob a building material, instead of just  
a mound of sandy clay.  and if you can't find straw, any hay of good  
quality - oat for instance, with long firm stalks - will work as well  
as straw.


On Jul 13, 2007, at 1:54 PM, Stacey wrote:

> Outside of tensile strength, straw is also very useful
> to add insulation to cob walls.
>
> If you are trying for natural conditioning (passive
> solar) design, this is especially important for north
> facing walls.  In fact, to build the entire north wall
> out of straw bales is not a bad idea.  But then again,
> in Georgia, you might not need that so much:!
>
>
>> What is the purpose of straw in a cob mix? Nobody
>> seems to "really
>> know" what the role of straw is anyway. Is it there
>> to hold the cob
>> together while the wall is still wet (like a free
>> form), or to keep
>> the wall from crumbling incase it cracks later (like
>> reenforcement),
>> or to allow air/water to move through the wall
>> (because straw is
>> hollow)? The problem is that nobody knows the reason
>> they used straw
>> because they didn't leave behind notes on how and
>> why they built that
>> way, and it's been a while since they lived here.
>> What do they do in
>> Africa? Do they use straw "in" the cob? Can any
>> other plants be used
>> as tensile such as long grasses? I'm almost ready to
>> start cobbing
>> but straw is just unavailable in GA right now, and
>> what straw there
>> is has a very high price on it. I'm not willing to
>> pay three times
>> the price for it if there's a substitution. I would
>> love to just go
>> out in the field and get some tall grass if it would
>> suffice. It's a
>> heck of a lot cheaper!
>>
>> Chow,
>> Damon Howell
>> North Georgia, US
>>
>>
>>
>
>
>        
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