Sv: Cob: Cob/light clay hybrid

[Shannon C. Dealy]

On Sat, 21 Apr 2001, kajchr wrote:

> The idea of building two separate walls with insulation between them might
> sound interesting to anyone who wants 3 ft. thick walls.... but there is
> one great danger in this system. It was suggested earlier that loose straw
> could be used for infill. This idea makes all my hair stand on end (Right,
> looks funny...). In case of a fire starting somewhere inside this wall, it
> will act as a chimney, or blowtorch, call it what you like. Fires are known
> to happen in houses of all kinds.... Remember Murphy´s Law?

This is only a danger if an opening is left in the wall after it is
filled, which is not a good idea even if there were no fire danger.
Completely enclosing the straw will help to protect it from moisture which
might get in under any number of circumstances such as broken pipes, roof
leaks, etc..  Of course it will also protect you from the fire danger,
since it takes a fairly substantial amount of oxygen for combustion to
occur, and there is no way that sufficient oxygen can pass through a cob
wall to sustain combustion.  Fire tests on straw bales covered with a
layer of plaster were unable to cause ignition of bales even when one side
was subjected to 1800 degrees F. for an hour.  For reference, paper
ignites at 451 degrees, aluminum melts at around 1240 degrees, and
brass melts somewhere in the 1800 - 1900 degree range.  This is why straw
bale houses have no problems with meeting building code fire resistance
requirements.

Shannon C. Dealy      |               DeaTech Research Inc.
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