[Cob] The matter of insulation. :)

[Janet Standeford]

Hi Mike,
I don't know if you saw my post regarding R value of cob. An energy 
model was done that shows it is R19 at 20 inches. I would think it gets 
awfully cold where you are but adding just 4 more inches would get you 
up to about R21. Then thermal mass would keep you pretty toasty with a 
stove.

On 5/10/2011 8:35 PM, Mike wrote:
> VEEEERRY interesting, Shawn!
>
> So you're basically doing a straw bale system with the bales super saturated
> with clay, huh?  I guess I worry a little about the compressive strength
> (enough for 12' walls?  and bearing a roof load?) - what are your thoughts
> about that?  I'm expecting the wall to be about 18" thick... so you're
> saying a base thinner wall of cob and then packing claystraw?  What's the
> layering you have in mind?
>
> And sand-clay-horse manure is exactly the plaster I had in mind.  Perhaps a
> lime mix as well for color and strength, but we'll see.
>
> R2/1" isn't so bad, really.
>
> Lot of "workshops" going up these days. :)
>
> On Tue, May 10, 2011 at 11:26 PM, Shawn King<sbkingster at gmail.com>  wrote:
>
>> Hi Mike, I have built an earthen oven insulated with clay-straw, and
>> it works very well to stop the transfer of heat.  I found some
>> research that clay straw is roughly R 2 to R 2.5 per inch, not far off
>> ubiquitous pink fiberglass.  When dry, the stuff is very tough, like a
>> connective tissue on the outside the cob. Basic earth plaster works
>> really well for a final coat (clay/sand/horse manure in the case of
>> the oven).  My partner Melissa and I are building a small cob
>> "workshop" in our suburban back yard and plan to use clay-straw to
>> outsulate the walls. You can start the layer thin just below the top
>> of the stem wall and curve it outward as you add upward so you get to
>> 6-8 inches of thickness.  If your cob walls are 12 inches thick
>> (roughly R 6 but that don't mean much), by the time you finish plaster
>> you may have R 20 conservatively, plus all that lovely thermal mass on
>> the inside, your walls still breath, and you can get it all done with
>> local and cheap or free stuff.  No, I haven't tested this idea on a
>> house, but if I can get my earth oven up to 700 degrees or so and the
>> outside of it is cool, with about 5-6 inches of straw clay as the
>> insulation, I think it would work well enough for a house.
>>
>> Best, Shawn King
>>
>> On Tue, May 10, 2011 at 7:41 PM, Mike<aspiringbodhisattva at gmail.com>
>> wrote:
>>> Hi folks!
>>>
>>> I'm in Chapel Hill, NC, where I've gotten permission to build a small cob
>>> workshop in my backyard (12x12x12 max, since they're not going to inspect
>>> the cob - just the electrical and plumbing I'll run to it).  Got the
>>> foundation and drainage trench dug and just about filled.
>>>
>>> I (shh) am hoping to be able to stay in this "workshop."  I'm curious
>> what
>>> options might fit cob Besides straw bales... I'm not a total purist (at
>>> least this time), and, for instance, lined the foundation trench inside
>> out
>>> and out to grade with R-5 1" thick solid foam board... more out
>>> of curiosity than belief it's the right application. :) Has anyone had
>> any
>>> experience adding a modicum of insulation into cob - I've heard of
>>> sandwiching foam board slices with wire to hold it together in the cob
>>> walls, though I worry about anything that might lessen the monolithic
>>> quality to the walls.  And while one cob book mentions you can plaster
>> foam
>>> board, I just can't see that working with how the boards resist moisture.
>>>   Just curious, any hybrid thoughts?
>>>
>>> Best wishes,
>>> mike
>>>
>>> --
>>> -------------------
>>> "The greatest achievement is selflessness.
>>> The greatest worth is self-mastery.
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>>> ~Atisha
>>>
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>>> are not only not indispensable, but positive hindrances
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>>> ~Henry David Thoreau
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>
>