[Cob] Buying bulk wool

[Clint Popetz]

On Tue, Nov 25, 2003 at 04:02:55PM +0900, D.J. Henman wrote:
> Clint,
>   I am having a hard time visualizing a cob greenhouse.   Could you 
> describe it a little for us.  For now I can only picture a three sided 
> cob structure with all glass on one side and  withtout sun coming in 
> from above either (since you're talkabout about an opaque roof).   Could 
> you explain what makes your greenhouse a greenhouse?   Sorry for the 
> confusion.

Sure.

You've basically got it right.  The greenhouse is an ellipse, with the
major access facing solar south.  The southern portion of the ellipse
(say, about 170 degrees of the total 360) is completely windows,
dumpstered from a local demolition.  The other walls are cob.  The
ellipse has a major axis of 14 feet, with a minor axis of 7 feet, for
an eccentricity of .77, which is pretty squished.  The total area is
99 sq ft, just under the 100 that would require a permit.  I chose an
ellipse to maximize area, minimize perimeter, and maximize southern
exposure.

The walls are 1 ft thick.  The roof is a shed roof, (covered with
about 6 inches of earth/straw/compost), at a pitch of about 15
degrees, with the high end facing south.  The windows on the south
side are pitched a little higher than 26 degrees, which is our winter
solstice sun angle.  (I pitched them a little higher because our
coldest weather is definitely not at winter solstice.)  The short
width (N-S), long length (E-W), and long/high windows (10 feet in run,
ending above the north wall by about a foot) mean that the entire
floor as well as all but the top foot of the back wall receive the
only strong sun my land receives.  For instance, right now, the only
sun they miss is from about 6:30am-8:30am, which is filtering through
neighboring trees and houses in the southeast anyway.  Ditto on the
sunset side.  The north side of the roof has an extra long overhang,
so that I could stack bales flat under it up against the north side of
the house for insulation, and they don't get rained on.  I am not
cobbing them in; in the spring I'll use them for sheet mulching the
rest of the land, and I'll put more bales up each fall, when straw is
cheap around here.

So yes, I definitely get the "a greenhouse made of earth?" question.
But the thing to try to envision is that because the windows on the
south side are slanted, it _does_ get sun from above.  But more
importantly, you don't _want_ the sun from above, at least around
here, because that's the summer sun (I'm at 42 north) and it's _hot_.
Most all-glass or all-plastic greenhouses around here either ventilate
like crazy in the summer, drape curtains to block the sun, or only use
the greenhouse for starts over-winter.  I have a friend her lost her
entire greenhouse crop for this year because of _one_ day of failing
to open the doors to let the oven-like temperatures fall.  She
basically baked months of work to a crisp.  So in our climate, where
winter can be 20 below 0 and summer gets to 100 degrees, it's
important to design for both ends of that spectrum.  West windows
would kill.  East windows give me little, due to neighboring trees.
And north windows, are of course, looney, at least in the northern
hemisphere.

And having sat inside it now for an entire day with the sun streaming
in and the north wall soaking up heat (and radiating it back into the
greenhouse all night,) I'm pretty optimistic :)

			-Clint