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Re: GSBN:Re Thermal Properties of Straw Bale Walls



Andre said, " As for the test Nehemiah mentioned where the top was stuffed.
A
> suggestions (if such a test is ever to be repeated) is to compress and
> stuff the wall from below with car jacks between the 'foundation' and
> botom plate'."

In an ASTM 236 Hot Box test, you do not have the opportunity/ability to
jack the wall segment up.  You build it upon the insulated (which is
pre-tested for conductivity) base, and you have a set opening size to build
up to - which is why you have to stuff the top once you have compressed the
wall segment.  If you COULD jack the wall up, you would be faced with
almost the same problem (only with jacks or blocks in the way) at the
bottom as we faced at the top.

Nehemiah Stone
stoneandstraw@...



> [Original Message]
> From: André de Bouter forum@...
> To: GSBN GSBN@...
> Date: 5/20/2007 3:17:00 AM
> Subject: Re: GSBN:Re Thermal Properties of Straw Bale Walls
>
> An other very effective way to create a snug fit arround the posts was
> shown at the last ISBBC: Put a piece of lumber (that has the dimension
> of your post) on the ground. 'Drop' your bale onto it .Cut of the excess
> straw that sticks out on the side oposite of the piece of lumber. "Et
> voila!"
> This trick only works for bales layed flat and with posts that are
> moderate to small in size. I forgot who showed us this 'gem' during the
> conference.
>
> Marty suggested that the 'French dipped' bales might give a good tight
> fit between the bales. My experience is the opposite. If the bales are
> dried after being dipped the diped sides get rock hard and do not
> compress. If the bales are placed before they are dried there is more
> chance for settling but this is a messier way of going about.
>
> As for the test Nehemiah mentioned where the top was stuffed. A
> suggestions (if such a test is ever to be repeated) is to compress and
> stuff the wall from below with car jacks between the 'foundation' and
> botom plate'.
>
> Bye,
>
> André "drop that bale" de Bouter
>
>
>
> John Swearingen a écrit :
> >> Straw-clay seems the best material for this purpose, although too
> >> much clay
> > might increase conductive heat loss in the stuffed area. <
> >
> > ...for several other reasons, too.  When straw is stuffed in joints it's
> > relatively loose and so provides a ready channel for moisture into the
> > depths of the wall.  Straw-clay will form a seal against moisture
> > entering
> > the joints between the bales.  In addition, it stops air infiltration
and
> > can be screeded off to make a flat plain for plaster, thereby reducing
> > the
> > occurance of cracks that result from abrupt changes in the thickess of
> > the
> > plaster.  Also, it's fun to get dirty....
> >
> > "Hurlen" John Swearingen
> >
> > On 5/19/07, Martin Hammer mfhammer@... wrote:
> >>
> >> Nehemiah -
> >>
> >> Good explanations.
> >>
> >> You talked about the straw-stuffed gaps at the top and sides of a
> >> wall as
> >> being places where convective losses could occur.  So I'll add the
> >> thermal
> >> importance of stuffing vertical joints/gaps between bales for the same
> >> reason of limiting convective losses.  (This would also be important
> >> between
> >> bales and "posts" that go mostly or all the way through the thickness
of
> >> the
> >> wall.  I've seen I-joists or steel trusses used this way.)
> >>
> >> Straw-clay seems the best material for this purpose, although too much
> >> clay
> >> might increase conductive heat loss in the stuffed area.  Horizontal
> >> joints
> >> between bales don't seem to be an issue because the weight of the bales
> >> appear to cause the surfaces to lock in well enough to limit air
> >> movement
> >> between them (although the French dipped bales might seal that joint
> >> even
> >> better, and bales on-edge probably nestle together better than
> >> laid-flat).
> >>
> >> Then there's always the question of what material is between the
> >> bottom of
> >> the plates, and what the insulative qualities of the roof bearing
> >> assembly
> >> are.  And then there's the ceiling/roof, and the windows/doors, and the
> >> amount of infiltration throughout, and . . . . .
> >>
> >> Martin Hammer
> >>
> >>
> >> > John,
> >> >
> >> > I did not see a response from Andrew.  Was that off list?  I am
always
> >> > interested in what new or other information people have on the
thermal
> >> > properties of straw bale construction.  Care to share his input?
> >> > Also, your Q about how compaction affects R-value is a potent
> >> question.  If
> >> > hot box testing wasn't so expensive and time consuming, or if there
> >> were
> >> > funders lined up to pay for it, I'd already have an answer for
> >> you.  There
> >> > are a number of confounding factors, so until someone has done the
> >> actual
> >> > research, we can throw around lots of theories.
> >> > For example, it is air that creates the insulation value of almost
> >> > everything used for wall insulation.  ,,,not the spun glass, not the
> >> solid
> >> > portions of the foam, not the cellulose, not the straw.
> >> Therefore, if
> >> > bales are compacted too much, one would expect the insulation value
to
> >> go
> >> > down.  But, what is "too much?"  If bales are too loose, then the air
> >> can
> >> > circulate in the air pockets and research HAS shown that this can
lead
> >> to
> >> > convective currents that lead in turn, to a dramatic drop in
> >> R-value.  That
> >> > was one of the causes (we think) for the relatively low R-values in
> >> the
> >> ATI
> >> > lab tests in Fresno, CA.  Once we stacked the bales in the hot box
> >> wall
> >> > opening, and compressed them as they'd be in a building wall, we had
a
> >> six
> >> > inch gap at the top.  We filled it with straw as tightly as we could,
> >> but
> >> > we are not match for either a baler or truckers' strap tightening
> >> levers,
> >> > so we KNOW that the top (where the greatest amount of heat exchange
> >> would
> >> > naturally occur anyway) was much looser than the rest of the
> >> wall.  Ditto
> >> > the sides, though those gaps were significantly smaller (so perhaps,
> >> harder
> >> > to compact straw into).
> >> > Further, though in theory greater compaction - after the optimal
> >> point -
> >> > will lead to a decreasing R-value, no tests have yet shown that to be
> >> the
> >> > case.  Perhaps we just haven't found the optimal compression force
> >> yet.
> >> > Perhaps the theory is wrong.
> >> > Lastly, I would question your assertion that jumbo bales are
> >> "naturally
> >> > compacted a lot more than the smaller bales."  It is mechanically
more
> >> > difficult to compact a larger bale to the same density as a smaller
> >> one.  I
> >> > am not saying that the machinery isn't designed to do so - perhaps it
> >> is.
> >> > But, from a pure physics point of view, it is not "natural" as you
> >> said.
> >> > One way to verify whether the compaction is greater or not is to
> >> measure
> >> > the water content and density.  Rice straw bales in California (the
> >> ones
> >> we
> >> > tested) are typically at least 8 pounds per cubic foot at a moisture
> >> > content of about 6%.  Do you have similar data on the Aussie jumbo
> >> bales?
> >> > If you want to get an accurate reading of the moisture content (more
> >> > accurate than a moisture meter stuck a random depth into the
> >> bales), let
> >> me
> >> > know and I will send you (offline) a description of how we did it.
> >> The
> >> > density (#/cf or kG/cM) is pretty easy, assuming you can weigh a
> >> > representative sample of the bales.
> >> > Hope this helps.
> >> > Thanks,
> >> >
> >> > Nehemiah Stone
> >> > stoneandstraw@...
> >>
> >>
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line.
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> >>
> >
> >
> >
> > --
> > John Swearingen
> > Skillful Means, Inc.
> > Design and Construction
> > www.skillful-means.com
> >
> >
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