[Strawbale] Convection in SB walls

forum at lamaisonenpaille... forum at lamaisonenpaille...
Thu Dec 9 09:51:23 CET 2010


Thanks Desert David for correcting what I understood of our conversation.

I see no point in trying to reduce the convection in the correctly built 
and plasterd SB walls (where all the holes are correctly stuffed). Ok, 
there is some convection in fibrous insulation material; probably 
because they contain larger air spaces than 'normal' insulation 
materials . But we still have VERY well preforming walls so let's put 
our attention on other details that make a well preforming building. 
Also, including 'solutions' for imaginary problems often create new real 

As for the performance of SB combined with panels; rather drawing a 
final conclusion from 1 test (even if it were done by the best experts) 
or a gut feeling I feel  that it is a field where I would first like to 
see a lot more hard data. Adapting Bruce's book 'Design of SB Buildings' 
to french made me realize that thermal testing is a very complex thing. 
That mistakes (in the protocol, in comparing and in drawing conlusions) 
are easily made and the numbers that come out give us, at best, a very 
limited vision of thermal reality. Still, they are clues to a better 
understanding. And then there is the real world... Herbert, are there 
any pasif house buildings made with OSB and SB that live up to those 

Thanks Carol for Jan Lacompte's paper 

I wish you all a nice day,

André - drowning in Cognac - de Bouter

Le 08/12/2010 23:59, Jan Hollan a écrit :
>> I've wondered what can be done about this. Convection needs height to
>> really get going so I wonder if some less permeable layer laid
>> horizontally between the layers of bales might reduce it some.
> My guess is it makes it worse, in the wall. It is not a pleasant thought
> for me, as I have insulated this way (using cardboard or paper) one wall
> already. It is better to let the air flow along the wall, as it makes no
> harm. The more convection cells spanning the full width of the insulation
> layer, the worse.
> The airflow/convection barrier should be perpendicular to the heat flux,
> like panes in the window. This is easy in roofspace insulation (two
> layers of small bales or many sheets of straw from jumbo bales). I'm doing
> it on walls as well, using one decimetre thick sheets from large bales put
> into a light wooden framework.
> Some maths concerning that is deep within the list archive... March and
> April 2005. Something more on that is in Czech only,
>               http://amper.ped.muni.cz/pasiv/slama/how_work.pdf
> yours moderator and list almost-no-reader
>    Jenik
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