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

fostertom at clara....uk fostertom at clara....uk
Tue Mar 8 16:05:15 CET 2005

Great comment Mark. Bales on edge? Woof! sounds dodgy - do they do that?
Is the Danish stuff available in English?

Tom Foster B.Sc.(Architecture) AECB
Tom Foster Architecture

-----Original Message-----
From: strawbale-admin at amper....muni.cz
[mailto:strawbale-admin at amper....muni.cz] On Behalf Of Mark
Bigland-Pritchard // Low Energy Design
Sent: 08 January 2005 14:35
To: strawbale at amper....muni.cz
Subject: Re: [Strawbale]Re: Strawbale digest, Vol 1 #474 - 7 msgs

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...)


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