[Strawbale]Hygrothermal behaviour of straw bales- Update of german test findings

[Dirk Scharmer - Architekturburo WAND4]

Hi!

Jan: In this moment I'm trying to be present on the 'passivhaustage' with a
contribution about the hygrothermal properties of strawbales. See you!

I'm convinced that the differences between the measurements of the specific
heat transfer value of strawbales are depending on minimum two factors:
1. the direction of the straw blades to heat transfer direction
2. the measurement method: The common Test according to DIN 52 612 or DIN EN
12 667/ DIN EN 12939 is an idealised one (two specimen one heat plate in the
middle and on both sides a cool plate). The common US-Test were plastered
walls are tested will be more realistic, I hope we will be able to do one in
future.

Our recent german tests (DIN 52 612) showed the following findings:
Straw blades in direction to the heat transfer: lambda10dry = 0,067 W/mK
lambdaZ= 0,08 W/mK, the same as mentioned from Rene and as found in several
international tests.
Straw blades transvers to the heat transfer: lambda10dry = 0,038 W/mK
lambdaZ= 0,045 W/mK, the same as in austria.
(Density about 90-110/kg/m3)(lambda10dry is the value measured on the dry
material at 10 degrees middle-temp., lambdaZ is the measured value + 20%
addition, because of the potentially difference at higher humidity. Thanks
Herbert, I partly stole this english explanantion from your message)
There had been more tests in germany, which are not certified but had the
same findings, including the interdependence.

To get more certainty about this interdependence, I just ordered two more
tests with the straw blades transvers to the heat direction.
I hope to have the findings in 4 weeks.

Concerning the moisture behaviour:
For the german technical approval of straw bales as an insulation material
we was challenged to prove that the straw bales do not molder in any case of
application. (But our favoured version is from inside to outside: clay
plaster 3cm, 46cm straw clay plaster 3cm, a ventilated wooden cladding in
the first step, in this moment it's to difficult to prove that only clay is
enough aginst driving rain)
We decided to do three steps:
1. install an hygrothermal measurement system in a sb- building
(www.fasba.de/projekte/strohpolis.html): DONE!
2. take specimens of built-in straw from 5 sb-buildings: DONE! Analyzing is
left.
3. do hygrothermal simulation with WUFI (http://www.wufi.de/index_e.html).
MISSING!
The simulation will show if there will be to much condensate or not.
All this findings will come in the following months and we hope to get the
german approval at end of 2005. We'll to get both lambdavalues in it, the
good one for straw blades transvers and the bad one for straw blades in
direction of the heat transfer.

You are all invited to take part in our german straw bale meeting on 1th to
3rd july 2005 in the near of Koblenz, may be it's useful to speak a little
bit german, I hope some austrian an switzerland balers will participate
(more on www.fasba.de/aktuelles/).

Beneath a lot of new sb-projects we will talk about test findings Approvals
etc.

Herbert, do you disagree?

Greetings

Dirk Scharmer


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