Cob in Snow

[Mike Carter]

Speireag Wrote:
> You're going to settle in an area which is potentially
>harsher than mine.
Average low for Sierra City (for example), CA, in January: 27.9 degrees
Average high was 47.1 degrees
See http://www.wrcc.dri.edu/summary/climsmca.html for other CA cities.
Even Susanville, which is more extreme than the Sierra Foothills, had an
average January low of around 20 degrees.  Twin Lakes (does anyone actually
live there?) was around 16 degrees.
There are significant temperature swings in the Sierras during an average
24-hour period, which thermal mass will help with.  Try and find the average
daily temperatures for your location.
>
>    We have harsh winters up here, though we're not at all far above sea
>level.  We get lots of snow most years, and I have seen overnight
>temperatures below negative forty.  I have lived and camped in the high
>Sierra, and I know that you will get lots more snow than we do here (though
>drier), and probably experience lower temperatures, depending on where you
>end up.
Agree on the snow - not so sure about the temperatures.
>
>    Cob is a nifty material in many ways, but it is not a good insulator.
>It is excellent thermal mass.  So, cob works well in climates where the
>average temperature over a day or two is not consistently much colder than
>comfortable.  Like adobe, cob's thermal mass acts to smooth out the daily
>temperature curve; it absorbs excess heat gradually, and then gradually
>gives it off when the air temperature drops below the temperature of the
>cob.
On the strawbale list, someone more knowledgeable than I stated that
for a given "R" value, you were always better off with more thermal mass
rather than less.  So wall thickness and the amount of straw in the Cob
(density) come into play.  Insulation and thermal mass both help.
>
>    There's the rub.  If the air temperature *stays* low, then so will the
>temperature of the cob.  Yes, you can make up some of that difference with
>passive solar techniques and by heating with some form of fuel.  That's
>what makes cob work in the winter as far north as Oregon and Washington.
This statement is actually true for any wall system, including strawbale.
The question is, "how much fuel?"  I don't know of any data yet.
Let's hear from some of the people living in Cob buildings in central
Canada, Colorado, etc.  I keep reading that Cob, like adobe, is only
appropriate for dry desert climates.  But this doesn't match the historical
use in Europe and Canada.  Some people told us Cob wouldn't work in the
South because of the high humidity and warm nights - we were surprised to
find that our average outside temperature was only 83 degrees (which thermal
mass takes you towards) when daily highs were around 95-100.
>
>    Beyond a certain point, however, you need more than thermal mass.  You
>need insulation.  I have talked to people who have lived in stone houses in
>Minnesota, and they tell me that they're great in the summer and really,
>really cold in the winter.  Cob is better than stone for insulation, but
>not by a lot.  For a continuously occupied building, you can do very well
>by enclosing your thermal mass inside an insulated envelope.  Then the heat
>transfer to the outside is slowed down, and the thermal mass acts even more
>effectively to keep things comfortable, especially in combination with
>passive solar techniques.
Yes!  I don't think we really know how much Cob differs from stone, as it
depends on the amount of straw used in the Cob.  We have tried to get
"minibales" of straw for "outsulation" on our structures.  Leichlem (sp?) -
straw coated with clay slip - could also be used (Gayle Borst idea).

(Rest Snipped)

Mike Carter
cobcrew at sprynet.com
Austin, TX    USA
(via Northern California)