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Re: [SB] GSBN:RE: From the Crest list
Thanks for the additional input. I have taken the liberty to put your
posting to GSBN to Repp including some additional points from me. Why
aren't you on the Repp list in its current form it is even better then the
At 06:32 AM 5/7/03, you wrote:
I used to be on the list but I guess I'm not sure I am anymore since I
didn't receive this except through Bbbbobbb. Oh Well.
In California, the accepted R-value (for compliance with the state building
standards) is R-30. That was based on a the results of a number of tests.
One that I managed while at the California Energy Commission (CEC), two at
Oak Ridge National Lab, the tests that Joe McCabe did, and testing that
Sandia Labs did. Every test had issues, and didn't all test the same thing.
I am aware of this I find it a pity that the circumstances and test method
are not that well documented. it makes comparing results and the appraisal
of found values very difficult. At least I have only been able to track
down limited information regarding the tests.
For example, McCabe and Sandia tested straw bales, while the other tests
were of straw bale walls. The best test (the last one at Oak Ridge) was of
two string bales, but extrapolating the conductance to three string bales
provides a value of R-33. The CEC, by the nature of its unique position in
the California construction community, has to be conservative in its
specifications; hence, R-30 instead of R-33.
To me the difference between R-30 and R-33 or even R-50 is a moot point
considering all other factors like window and roof details and other
possible cold bridges. Its no a sum of parts but the whole system poperly
put together that counts. I think that this is a matter we should be
stressing much more considering some recent reports of the poor thermal
performance of certain SB houses.
Sheet rock is flamable, at least enough to feed ignition somewhere else.
The paper coating on sheet rock will burn and burn hot. Sheet rock is a
very bad choice for finishing a bale wall - even if it weren't for how much
nicer looking a plastered bale wall is than flat gyp board.
I fully agree, besides once the paper is gone how long will the sheet rock
stay intact and what about the joints between sheets?
Did you have a look at the recent CSIRO fire test yet? They are a very
strong case for the fire resistance of SB as you might be aware CSIRO have
probably the toughest fire test criteria in the world. They tested various
stuccos there with little difference between results. The test samples were
made by an experienced SB builder with a reputation for good work. He
expressly did not endeavour to do a better job then normal on the samples
because he wanted the test to be representative.
When we built my house, we held a propane torch to the side of a bale for
nerly five minutes. Less than thirty seconds later there wasn't even any
On my site www.rened.cistron.nl on the SB house page the Vreeland barn
shows a few pictures of such a SB inflammability demo. The story is half
true because if you put a sufficient heat load on a not stuccoed bale, not
just a Bunsen burner it will eventually explode into flame. The integrity
of the stucco itself is also very important in preventing fire because at
the high temperatures of a real fire the stucco is also acting as a heat
insulator preventing rapid heating of the straw.
We then broke open a bale and lit the loose straw. In less than
thirty seconds we had a flames over fifteen feet and building fast. Trying
to burn tightly packed bales is harder than burning a phone book. Trying to
burn loose straw is easier than burning a pile of phone book pages,
individually ripped from the book, and wadded up.
Loose straw on building sites is a serious fire/safety hazard and should be
cleaned up as soon as possible. I am therefore not very keen on the
concept of notching bales or any other techniques carving bales which
produce loose straw. I prefer 'leicht lehm' and the rapid application of
the first stucco coat
Best to you all.
From: Bob Bolles [mailto:Bob@StrawBaleHouse.com]
Sent: Tuesday, May 06, 2003 6:17 AM
To: Nehemiah I Stone; Nehemiah I Stone
Subject: From the Crest list
Date: Mon, 5 May 2003 14:55:07 +0200
From: Rene Dalmeijer rened@...
Subject: SB r-value and fire resistence
At 06:00 AM 5/4/03, you wrote:
>If in Calif. they only "give you" 29 for bale, does that mean the R value
>the bales is really 29? Probably not. What they really need in Mongolia
>a true high R value.
The recent ORNL 1998 tests seem to indicate that r-value is nearer R 29
(3string bales) then any other value. I have the impression that to some
this is disappointing and not enough after the initial R50-55 (3string
bales) values based on the 1993 McCabe tests. But in effect the 'low' R29
is at least 2 x better then most modern mainstream wall structures. In
effect a SB wall properly executed without cold bridges will perform quite
a bit better then stick frame. It is very difficult to avoid cold bridges
in stick frame. Some of the recent reports for under performance of SB
buildings are not due to low r-values of the walls but mainly due to
excessive air leakages due to poor detailing at roof and floor
>I'm not arguing that air in the bales wouldn't up the R value -- I don't
>know -- seems to make sense.
A tightly packed bale does not seem to impair its insulation value that
much because it precludes air movement within the bale thus avoiding
convection losses. The ideal insulation with air is having lots of small
disconnected airspaces therefor a loosely packed bale could have a poorer
thermal performance then a tightly packed one.
>But w/r/t fire inside a stuccoed wall -- I've
>always wondered how houses -- and even steel buildings -- burn when the
>is between stucco and sheetrock, which I assume is also not flammable. As
>long as it has a burnable roof, if the stuff inside the walls (studs,
>straw) is also burnable, maybe it's a fire hazard.
Most materials are flammable given a high enough temperature. To reach the
required temperature requires sufficient fuel to build up the needed heat.
The reason why a SB wall can perform so well regarding fire resistance is
1) A complete intact stucco covering,
2) No airspaces,
3) Its own the insulation,
4) Tight packing of straw.
Therefore airspaces in the SB walls, loose straw and lightly packed Bales
are not so good for fire resistance. Another point to note is that every
penetration of the stucco surface creates a potential fire path (and air
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