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Kiko Denzer on Art

[Cob] Beginner with lots of stone

Barbara Roemiller roemiller at
Mon Feb 4 15:21:25 CST 2008

HI Devon,

It's a fine idea to build an ag.structure first,and great that you
want to make use of native materials.  While we've helped some others
build their cob homes, we will include cob as part of a hybrid when we
build.  Straw is a much better insulator than cob, and that's a
concern for our northern California location at about the 39th
lat.line, and with a total annual Farenheit heating degree day figure
of 4770.  You might start by considering Ianto Evan's interest in very
thickly plastered (really cobbed) straw walls as the ideal
insulation/thermal mass sandwich.

Have a look at many beautiful cob projects and his own house on Rob
Pollacek's site,

We live about four miles as the crow flies from most of the California
Cob sites.  I just talked to a friend this morning about Rob's house.
His foundation/floor are apparently cold, as his plan to use hydronic
heating is anathema to something in his earthen floor, perhaps the
wax: the floor softens when the hydronic is used, so it's turned off.
The friend down the road who told me that this morning is about to
move into a lovely hybrid timberframe/cob/straw clay house her husband
built.  Their earthen floors are cold because neither the foundation
nor the floor are insulated.  The foundation is massive stones, cobbed
and mortared together - pretty hard to insulate.  They would probably
use a rubble trench foundation with stone applied in order to provide
a base that could be insulated.  We will do a rubble trench with slip
form for our hybrid, and the foundation and perimeter of the
slab/earthen floor will be insulated, too.  You might consider slip
forming walls since you have a lot of stone - great thermal mass and
could be combined with all that straw for a very cozy place.  Slip
forming is much less labor intensive than large stone placement,and
not always such an aesthetic compromise.  Slip forming the cob is much
faster than the loaves method, too.  It's all pretty labor intensive,
but that's what most of us have more of.

If you are in a seismic zone (and not much of California isn't),
you'll want to consider how to approach the issue of stability and
creating a monolithic foundation.  Cob is not suitable for holding
together stones, even large ones, in most seismic zones.  Our
neighbor's house is owner/builder permitted, and his foundation
included lots of steel, drilled into his stones and attaching them to
his concrete.  We are in seismic zone 3.  We'll have our foundation
engineered, even if we build with an owner builder permit where such
engineering is not required. (Actually, we hope to advance the cause a
bit and plan to have engineering done not only for the foundation but
for a loadbearing bale/hybrid house.  The building department has
assured us that they will permit a LB home with engineering.  There's
been a lot of alternative building in our county -Nevada County - so
building inspectors don't look perplexed when we talk about these

Best of luck in using what's at hand wonderfully!