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GSBN:RE: From the Crest list
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.
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.
Tighter bales and tighter construction have consistently given better
R-values in the tests. One of the tests provided a very low R-value,
principally because there was relatively loosely packed straw filling up the
space between the top of the wall and the hole into which it was built at
the test lab. Another got low values because the stucco did not adhere to
the surface of the bales and there were convective currents between the
straw and stucco.
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.
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
smoke. 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.
Hope this helps.
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
Hola Mr. Stone
We missed you at Cambria, Amigo
Care to respond? If you aren't a member of the list, you can send it to me
and I will send it to the 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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