[Cob] The matter of insulation. :)

[Shawn King]

Hi Janet, Mike, all,

I think outsulation for cob may be essential in cold climates - I do
not believe you can rely on thermal mass to stay warm and respond to
heating unless outsulated.  Unlike a conventional wall, which has
little or no "U" value (thermal absorption and release), earthen
material walls will radiate at their temperature, which is why an
earthen building will feel cool in the early summer when outside air
let into the house through doors and windows is hot (and vise versa in
cool weather).  Over a long cool/cold season, if not outsulated, cob
will gradually take on the outside average temperature, which might be
50 degrees F for several months.  Once cold, no stove will be able to
keep up - you might heat the air, but the walls will be at a radiant
temperature in the fifties, which will feel cold no matter how warm
your air is.  Your body reads radiant heat first, air heat last.  This
explanation is supported by experience with superadobe earthbag domes
in cold climates.  These buildings will have 16-18 inch thick
compacted earth walls, and are uninhabitable in the winter once the
wall mass cools down.  The cooling down will take a month or two, but
once you are there, a small home heater will heat the air in vain. I
believe this is why Cob Cottage is moving towards building with
bale-cob, a hybrid 8-10 inch cob wall on the inside and a half-bale on
the outside, covered with plaster.  The bales are cut with a chainsaw
and pinned with trimmed roundwood stakes for stability. Clay-straw is
my shortcut to avoid purchasing and cutting bales - we have plentiful
dried wild oats all around here in the Sacramento area of California.

If anyone has other experience with keeping a non-outsulated cob house
warm in a cold-winter climate, please advise, thanks!

Best, Shawn

On Tue, May 10, 2011 at 9:55 PM, Janet Standeford
<janet.standeford at gmail.com> wrote:
> 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.
>>>> The greatest quality is seeking to serve others.
>>>> The greatest precept is continual awareness.
>>>> The greatest medicine is the emptiness of everything.
>>>> The greatest action is not conforming with the worlds ways.
>>>> The greatest magic is transmuting the passions.
>>>> The greatest generosity is non-attachment.
>>>> The greatest goodness is a peaceful mind.
>>>> The greatest patience is humility.
>>>> The greatest effort is not concerned with results.
>>>> The greatest meditation is a mind that lets go.
>>>> The greatest wisdom is seeing through appearances."
>>>> ~Atisha
>>>>
>>>> "Most of the luxuries, and many of the so-called comforts of life,
>>>> are not only not indispensable, but positive hindrances
>>>> to the elevation of mankind. With respect to luxuries and comforts,
>>>> the wisest have even lived a more simple and meagre life than the poor."
>>>> ~Henry David Thoreau
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>>
>>
>
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