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Re: Strawbale engineering

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Our firm has engineered about a dozen straw-bale residences.

California was experiencing major air pollution problems from burning
rice-straw after the grain was harvested, and passed legislation with
prescriptive standards for straw-bale homes (i.e. if you meet the
standards, the local jurisdiction *must* allow you to build the
home).  The prescriptive standards are for load-bearing walls, but
they are pretty limiting as far as window opening sizes and such. 
Most of the houses we have designed were post-and-beam structures
with straw-bale infill.  An Architect or PE must do the design for
either sort.

As for fire-resistance, once you plaster or stucco the bales they are
essentially fireproof.  Even without stucco or plaster, it's really
hard to light a bale of compressed straw on fire--the only real fire
danger is during construction when loose straw accumulates as bales
are notched out to fit around posts and such.

It seems as if the building methods are still being refined, which is
a bit of a pain for us as engineers because the details we used on
one house are out of favor by the time we design the next one.

As I understand, the first straw-bale houses were built in the 1920's
in Nebraska (not what I would consider a 'dry' climate) and some are
still standing.  But that does not mean that none of the others
failed and turned into compost.  I would put language in a contract
stating that the building method is still experimental, and the house
may experience settlement, creep, cracking of finishes, etc.   And
that waterproofing is NOT my responsibility--which I put in all my
contracts anyway (especially after finding that the roof of the house
I'm leasing leaked for 15 years into the walls behind the tiled
shower;  I think the tile has become the main structural element
there....)

Straw-bale houses can be just as sturdy and long-lived as any other
house when designed and built properly.   And the energy performance
is amazing, from the owners that I have spoken with.  I'm waiting for
someone to treat the straw with borates to make it fire, insect, and
decay resistant (like they do for cellulose insulation).

Thor Matteson, SE
www.shearwalls.com


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