[Cob] The matter of insulation. :)

[Shawn King]

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
>
> --
> -------------------
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