[Strawbale] SB R-values German tests
Dirk Scharmer- Architekturbüro WAND4
info at wand4...
Wed Mar 18 13:19:06 CET 2009
Herbert, André, Peter, ...
I sent our last test results directly to André. Herbert, I think you
know the Austrian activities very well but let me speak for the German
results and approvals:
In Germany we did about 15 lambda-Value tests (thermal conductivity)
according to EN 12667 since Mai 2003 (Attention! Herbert used
accidentally the term 'R-Value' which is not the conductivity but the
thermal resistance). We found a variety of values mainly depending on
density, humidity and fibre orientation and probably fibre length (type
Our best value was lambda 10,dry= 0,038 W/mK and our worst
lambda10,23/80=0,082 W/mK. We found conversion factors from dry to wet
between 1,07 to 1,2.
We tested densities (dry) from 80/ to 116 kg/m3. We tested wheat and rye.
The official approved "Baustrohballen" can be calculated perpendicular
to the fibre direction with lambda=0,052 W/mK (max. lambda dry=0,044
W/mK+ 20% addition) and in fibre direction with lambda=0,08 W/mK (max.
lambda dry=0,067 W/mK + 20% addition).
Our current goal is not the maximum optimization of the lambda value but
the maximum optimization of the usability of local bales which are
produced under normal agriculture conditions. For this it is more
important to provide a calculation lambda value which covers the variety
of occuring lambda values to avoid failing of some bale charges (the
distributor has to sign for the compliance of the properties).
I think we should have a session at the ESBG in Belgium in August to
this topic where we first present the current knowledge and the country
results to each other. After heaving heard the international results and
approaches we should of course discuss, e.g. lambda value optimization,
fibre direction, humidity, density and strategy, ...
And to avoid another confusion: "Baustrohballen" are of course "normal"
straw bales and I think there is not a difference to normal austrian
bales (of course we saw differences in past between bales from different
countries depending on the baler, on the acre, on the type of corn, on
the type of cultivation,.... "Baustrohballen" are produced directly on
the fields with normal balers (common ones in Germany: Welger ap 53,63
and 630 to 830, or different types of John Deere or Claas,...)
I'm keen to see the new Austrian test reports and how you managed to
optimize the lambda Value (pressing method?) and how you want to ensure
the thermal quality while the production of the bales.
And last but not least: Straw is not equal to straw, testing procedures
not equal to testing procedures and countries approaches not equal to ...
And please have in Mind: Most of the international R-Value-Tests (now
I'm speaking about the resistance) shows much higher recalculated
lambda-Values >0,06 W/mk as the Germans and Austrians are talking about,
on more reason for me, not to count on the best values.
Fachverband Strohballenbau Deutschland e.V.
c/o Dirk Scharmer
In de Masch 6
Tel. 0049 4131- 727804
Fax. 0049 4131- 727805
Email: ds at fasba...
> Peter, this is wrong...
> These are not the official R-values for Germany. The official R-Value for
> usual strawbales in Germany and Austria is 0,045 W/mK.
> These are the R-Values for "Baustrohballen", special bales tested under
> special circumstances.
> And it is an old but wrong conclusion, that the worse R-values are more
> We developed and tested those special strawbales for the building-industry
> (for prefabricated walls and roofs) in 2008/2009 again in Austria and had
> much better results in 2 different official testing-institutions: 0,047 W/mK
> (inluding the 20% addition) although there is no test-paper available yet
> (we are still optimizing...).
> The difference between "normal" strawbales and "Baustrohballen" is the
> testing-procedure according to EU-building-codes, but it is possible to
> press those building-bales for prefabrication in a whole different way, than
> Dirk did. It's all about pressing the bales in the best way.
> So we will have CE-certified "Baustrohballen" with nearly the same good
> R-values as the R-values for normal strawbales in Austria and Germany this
> Best wishes, Herbert
More information about the Strawbale