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Re: GSBN:Re Thermal Properties of Straw Bale Walls



Dear Nehemiah,

Apparently I did not get across what I intended to say. But it's not
that important.

As for stuffing the top of a post and beam structure, this is how I do
it (and I'm convinced  it is almost as dense as the rest of the wall) :
First place your bales to form your wall (* keep in mind that in France
the bales are usually placed on on top of one another, squished between
planks of 4x20 cm (2x4 inch))
When we get to the last row that can be placed we do NOT place them.
Instead we place a thick plank which we push down with a carjack. This
pushes down the bales, eliminating any (horizontal) voids between the
bales and making the wall a whole lot sturdier. We then prepare the
custom bales that will fill the space between the last bales posed and
the ring beam. To avoid stuffing with flakes (this is my main point) we
place those custom bales vertically thus filling the space of the last
row of bales + the space above it (and you bet you your bottom dollar
that MY custom bales are as dense as any bale coming straight out of a
baler ;-). When the custom bales are ready we take out the jack (the
bales bounce up a bit) and place the bales. We use 'shoe horns' made of
sheet metal to make sure the bales slide in as tight as possible without
the need to force a lot (I hope the word 'shoe horn' is correct, what I
mean is the metal object one uses to get in those very tight dancing
shoes). By the way the sheet metal is folded on one end so that it is
easily pulled out again. The bales will come up even more and this
creates an even pressure throughout the wall (at least we think so).

* car jacking a whole wall down is obviously tricky, but for a test
panel this should not be that difficult.

This said, I also like Bob's idea to cut out a piece of a larger wall.
But cutting would need to be accurate and handling could be difficult.
And I agree with wolfman that eliminating the the post and beam
structure using big bales is a very interesting way to go (but one would
need a crane to dip them ;-)

Bye,

Stuffed up Andr?

PS thanks Martin for Darrel DeBoer's email.




Nehemiah Stone a ?crit :
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 ?crit :

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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--
John Swearingen
Skillful Means, Inc.
Design and Construction
www.skillful-means.com


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