[Strawbale]Re: Strawbale digest, Vol 1 #474 - 7 msgs

asbn asbn at baubiologie...
Tue Mar 8 17:11:38 CET 2005

Dear Mark

If you want to know the difference between e.g. cellulose, sheep-wool, flax,
fiberglass and strawbale, our tests give a relevant result (all are 0,045),
even when the thickness of the measured probe is smaller than that of a
strawbale. All of these insulation-materials act different in reality or
when wet. But for all organic insulation-materials there is a 20% addition
in value by way of calculation for that reason (not so for fibreglass). And
all are measured under the same conditions.

When you have to prove the insulation quality to officials to get better
financial supplies when you build, these tests are relevant, because this
paper is the only thing that matters and all common building-engineers use
these tests for energy-analysis.
We all - networkers, builders, architects, officials - know, that reality is
a different thing, even one (passive)house doesn´t act as the other one. But
as long as we have to compete with cheap prefabricated-houses or expanded
polystyrol-passive-houses, truth is on our side, when we rely on our tests.

Strawbale-(passive)houses in Austria are usually build with this
construction / wall-system:
1,5 ­ 2 cm limeplaster on facade
3 - 5 cm magnesiabound Heraklith-plates (woodchips)
2,4 cm diagonal wood-boards
35 cm strawbale with 6 x 35 cm construction-timber (sometimes in a
dual-sandwich-system, isolated with 5 cm cork)
2,4 cm wood or OSB-boards*
3 - 5 cm magnesiabound Heraklith-plates (woodchips)
2 - 5 cm clayplaster (thickness depends on wall heating-system)

*If OSB-boards are glued, wind-protection-folie is not necessary.

Blower-door-test is obligatory if you want a financial (eco-)supply by the
government in Austria.

This wall-system has many advantages (e.g. easy to use installation-level in
Heraklith-boards). And I´m sure, this is a passivehouse-system, U-value
around 0,12 - 0,14 W/m2K. For sure it is a safe (and therefore accepted)
system (post-and-beam-construction) for countries with much and cheap
wood/timber (not so for Denmark).

Best wishes from Austria
Herbert Gruber, ASBN

08.01.2005 15:35 Uhr

> Dear all,
> The low lambda results in Germany, Austria and Denmark are indeed based
> on official test procedures, and appear to be reliable.  However, in
> these procedures, (i) the thickness of bale used is smaller than that
> for a wall assembly, and (ii) only very dry material is used.  Hence, if
> (a) there is any heat transfer effect which isn't proportional in its
> extent to the thickness of material, or (b) if moisture movement makes
> any difference, these tests will not be directly applicable for U-value
> calculation without some sort of adjustment factor.  There is reason to
> believe that convective effects, including moisture transfer, do make
> some difference in a real-life wall assembly.
> This indeed appears to be the case when we look at the whole-wall
> U-value tests carried out by ORNL and by the Danish testing programme -
> both to variants of official test procedures in the countries
> concerned.  These give significantly higher U-values than can be
> explained by the lambda values.  There is some useful discussion of this
> in the Danish summary document:
> Munch-Andersen, J & Møller Anderson, B (2004),   Halmhuse: Udformning og
> materialeegenskaber,  By og Byg resultater 033, Statens
> Byggeforskningsinstitut, Hørsholm, Denmark
> which is available online in .pdf format at the By og Byg website.
> Realistically, I would not assume a U-value of less than 0.2 W/m2/K for
> a 2-string-bale wall laid flat.  The results seem to me to suggest that
> you'd get much the same for the same bales laid on edge.  (Though I
> personally have big doubts about on-edge bales for other reasons...)
> Mark

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