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Cob: Re: Thermal Mass and R-values

David KNAPP AAEEE5K at gwia.rkd.snds.com
Fri Aug 20 15:57:36 CDT 1999


Tom,

It is probably assumed by everyone, but I just wanted to add to the cob-SB discussion a bit.  I think the SB insulation on all four walls in severe climates is wise.  Due to the resulting thickness of the resulting wall however, the windows can end up looking like mini caves.  It would really enhance the feel of light and openness in the room to bevel the cob-SB walls at each window.  This would not hurt the structural stability of the cob wall if the angle is not too shallow.  To be sure, extra attention to the lintel should be applied.  It would also make a very nice area to place plants or to read a book on a sunny day in the winter.

If we build in NW Illinois, I am looking at a similar type of construction, except I would probably go for the light or medium timber frame and then do cob-SB fill in.  This is to avoid the potentially large battery of destructive testing and engineering expenses to get the local building departments approval.  We also want to install a living roof similar to what Rob Roy has installed on his NE NY Earth sheltered cordwood masonry homes.  Properly engineered, this would really help you with keep warm in the winter.  The snow load on the living roof acts as an additional insulation layer.  Rob Roy's living roof has lasted well for nearly twenty years now and shows no sign of needing repairs anytime soon.  His only hiccup was some carpenter ants that required a small easy to do repair.  An annual inspection and application of non-toxic Diacotamous (SP? Sorry) earth to any visible insects.

Dave Knapp
Winnebago, Illinois
Renewables at earthlink.net
http://www.bigfoot.com/~renewables/

>>> "Tom Fetter" <tom_fetter at hotmail.com> 08/20 10:25 AM >>>
Hi Tony.

Based on what folks said in reply to my similar query a while back, I'd 
probably encase strawbales within a cob wall -- more cob on the inside of 
the house (for structural and mass reasons), and either a thinner cob wall 
on the outside of the bales, or a thick mud plaster (which, if straw is 
incorporated, amounts to much the same thing).

...

Tom Fetter.