Cob: Insulation

This message is really just from Mark (as opposed to the last one, for which we are equally to blame.   :-)

On Thu, 24 Aug 2000 10:03:23 Russel Johnsen wrote:
 >Another avenue we are considering is a stack wall cob
 >hybrid.  The more insulative stack wall would be the
 >outside with a cob thermal mass interior.  Both walls
 >breathe so they should be compatable.  

This is something I've considered as well. The thing I haven't liked about cordwood, even out at Rob Roy's, is the shrinkage of the wood from the cement matrix (which would also happen if cob was substituted for the cement). Truly, when this happens a building very literally breathes. These air leaks can be an enormous source of thermal loss. With a direct-applied plaster (preferably on both sides, and as thick as a person wants - as in cob), these air leaks would be eliminated. Where there's plenty of deadfall, appropriate thinning/harvesting, or after-slash cleanup (sigh), I like cordwood. Except for the cement use.

 Last time I talked to Rob Roy (sheesh, it's been, like, two years now), he'd got wind of a cordwood house in Wales where they used cob instead of cement mortar. He didn't know any details, and I haven't heard anything since.

FWIW, building scientist John Straube of the University of Waterloo (Canada) alluded a while back that a small uninsulated mass-walled house could potentially "work" in severely cold climates, and have similar heating-energy requirements to a well-insulated structure with comparable interior space. He supposed the walls would need to be on the order of 3'-4' thick, and a frequent or constant heat source would be required inside the structure. Who wants to research this and report back to the list?   :-)

Mark Piepkorn
duckchow at greenbuilder.com


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