Cob: strawbale/cob on the inside

[Tom Fetter]

As another Albertan interested in cob buildings, I've been a bit surprised 
that some folks haven't realized the necessity of insulation when building 
in as extreme a climate as this one.  There's simply no way that an 
uninsulated wall of any material can collect and hold enough solar gain to 
counter weeks on end of daytime temperatures averaging -20 degrees, with 
night temperatures another 10-15 degrees colder.  Even the most efficient 
thermal flywheel has to deal with long-term ambient temperature as well as 
solar gain.  I have also wondered about a hybrid, using strawbales on the 
outside, cob on the inside ... or maybe a 4-6 inch thick layer of 
cob/earthen plaster on the inside of strawbales to get the thermal mass 
benefits.

The stumbling block in my mind has always been how to adequately protect an 
external earthen plaster from cracking/spalling in the repeated freeze/thaw 
cycles we regularly have at either end of the winter.  Through November, and 
then again for about 7 weeks in early Spring, we often have humid days (as 
snow/ice melts) and freezing nights. This regularly cracks commercial bricks 
that haven't been fired at high enough temperatures to resist taking up 
moisture.  Given that, it makes me feel doubtful that a wide roof overhang 
and a high foundation would be adequate to protect unfired earth.  I'd 
appreciate any ideas ....

Tom Fetter.

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