[Cob] RE: Stone-Cob Hybrid

[Barbara Roemer & Glenn Miller]

Lori wrote:

>   All the code issues with cob and suggestions for strawbale-cob hybrids,along
> with some reading about the Nearings stone buildings have made me wonder if
> cob could be used as the interior for a stone building.A stone exterior,loose
> straw for insulation,and cob interior walls,if the stone were to support the
> roof,it seems like the biggest issue with the codes is getting cob approved as
> a load bearing structure.

I'm sure you could combine stone and cob in this way, though I think the
resulting structure, in most climates, would be less advantageous than
straw/cob hybrids.  The advantage of cob/bale hybrid is that the mix
provides both mass and insulation, and puts them both where they make sense.
Stone and cob both provide thermal mass, a redundancy. Straw in the middle
will provide some insulation, but you'd have better R values if you
increased the thickness of the straw and included less mass, keeping the
straw insulation on the outside, rather than in the middle.  Stone is
difficult to work with in seismic zones: it has to include rebar and cement
mortar, both EE materials, which is why it's generally limited to
foundations where it can be easily insulated.  Ianto Evans of Cob Cottage,
recognizing the benefits of both cob and straw, suggests load-bearing straw
with interior heavy cob plaster for zones that need higher R values.

We are in seismic zone 4, in California's Sierra Foothills.  Cool wet
winters of 7 months, and hot dry summers.  We will build LB straw for
insulation and sound control, heavy plastering/cob for fluidity, niches,
curves, and mass, and straw/clay partition walls for the best properties of
both materials.  All three techniques are easy to work with, and have less
EE than mortared stone with steel... Because of the seismic considerations,
any structure here has to address engineering for shear, as well as uplift,
snow loading, etc.  While my county hasn't yet had an application for LB
bale, building officials do not expect any problem with approval of
engineering.

Barbara