[Cob] The matter of insulation. :)

[Shawn King]

I find the grab to be pretty good, at least on the earthen oven, but
building the clay straw simultaneously with the cob, and working the
clay straw a bit into the outer inch of the cob would be better.  If
you are adding the clay straw after your wall is built, build upwards
just like it is cob, starting at or near max thickness at the base,
doing a lift of 6-10 inches, then letting it dry/set up before doing
another lift. The clay straw will have lots of air pockets and
crannies for each subsequent layer to grip as you go up.  I recommend
not adding a thin layer to your entire cob wall, then another thin
layer, etc. like you would a normal plaster.  I can try and draw what
I mean and send it to you if that would help. Tapering walls a little
as you go up is often a good idea as long as you don't loose too much
width near the top for supporting the weight of a roof.  Under 8
inches thick for a non-curved wall not recommended.

Other than that, max your passive solar arrangement.  You may already
familiar with all this. South wall should be where your windows are,
outsulate the other walls and not the south (unless the whole building
is shaded in winter), minimal windows on the north wall.  I have an
idea for what I call a tromb wall bay for adding passive solar glass
to a wall without making another window, but I haven't drawn or built
it yet.  I am so bad at drawing that it is often easier to just build
a model and take pictures!

On Wed, May 11, 2011 at 7:19 AM, Mike <aspiringbodhisattva at gmail.com> wrote:
> Again, Shawn, Janet, thanks for weighing in.  I spent nights with a good
> friend I was dating at the time in a small, 1-story 200 sqft or so cob
> cottage with an earthen top.  The north wall was straw bale turned on its
> side (still over 2' thick)  It was COLD in the winter time, but her little
> stove pounded heat into that small of a space.  You had to be more mindful
> about setting heat so it'd be ready at night, but it was livable... though
> it was some serious roughing it at times, just in that it could easily drop
> to 40s in the cottage if you aren't mindful about heating it.  I don't get
> the benefit of a radiant heat stove - because of the plumbing code folks
> here, they're making me put in a baseboard heater (that I'll probably offset
> with panels, but still) - I doubt it'll have the same ability to heat the
> walls as that stove seemed to.  I've heard similar R values for straight
> cob, but also have absolutely experienced its thermal mass qualities for
> warmth AND coolth - winter mornings, after a nighttime of absorbing freezing
> temps, were quite chilly.
> With the two methods you mentioned - half-bale (cob-bale) walls, and
> clay-straw (which sounds more what I'm interested in) - how's the
> "grabbiness" of the clay-straw?  And application - do you do a whole thinner
> wall (1' at base, 6" at top) first and then work the outside, as if you were
> plastering?  Or work as you go, building "out" as much as you're building
> up, a sort of half-and-half mix approach trying to really tie the clay-straw
> inches (6" all the way up let's say) into the cob inches?  I can't quite
> picture the building of it - multiple layers seems like you might not get
> that tight bonding by thumbing into the cob like you do with a traditional
> monolithic cob wall...
>
>
> On Wed, May 11, 2011 at 9:54 AM, Shawn King <sbkingster at gmail.com> wrote:
>>
>> 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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>
>
>
> --
> -------------------
> "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
>