[Strawbale] Big bale insulation values (Derived from 'Repair work on danish strawbale house')

Dave Howorth dave at howorth....uk
Wed Oct 5 22:15:14 CEST 2011

I don't know about the insulation value. I suspect a test would be the
only way to be sure.

I think the condensation question is a 'red herring'. It doesn't matter
how thick the wall is, if it's warm inside and cold outside there will
be a condensation point in the wall. There is one inside a conventional
'small' bale wall, but it isn't a problem.

There are three ways to stop that being a problem. The simplest way is
to build from some material that doesn't really care, such as brick.
Another way is to stop the water vapour entering the wall by adding a
vapour barrier on the inside of the wall; that's what's usually done
with timber frame houses.

The third way is to make a 'breathable' wall where the vapour can enter
the wall and can even condense in the wall, but is also able to emerge
from the wall as either a liquid (by capillary action) or a gas (by
diffusion). That's what happens in a straw bale wall. You can also build
timber frame like that as well, by using so-called 'warm' construction,
where the condensation occurs in external insulation.

Cheers, Dave

On Wed, 2011-10-05 at 16:16 +0200, Max Vittrup Jensen wrote:
> Dear all, 
> The last question by Michael Jorgensen brings up an issue discussed
> during our recent 'Big Bale Building Basics' workshop. An issue which
> none of us were able to answer satisfactory, and which we'd appreciate
> input on.
> As we cut through some of the big bales (70x120x1900), (which we
> stacked on edge) it was evident that the individual straws was
> extremely compressed, much like what you see when you cut in some of
> the 'Stramit' panels (in CZ: 'Ecopanely' ). It's visual in this
> album:https://picasaweb.google.com/permamax/BBBB2BigBaleBuildingBasics?authuser=0&feat=directlink
> We deducted that a BB gives less insulation per cm3 than small bales
> (but as it's thiker it's fine), however also less air movement.
> Question is what how the real parameters look like? It also brought up
> the issue of diffusion when building with big bales to passive house
> standards. A concern was that a BB wall would need a moisture break
> membrane due in order to ensure the condensation point didn't occur
> within the bale
> This is all well beyond my humble knowledge... Any rocket scientists
> out there?
> Cheers,
> Max
> > > In your experience will bigbales have a relatively better insulation
> > > effect than the small traditional ones. My thoughts are that they
> > > are very heavily tightened and there the free floating air inside is
> > > less than in the small bales (relatively). Am I wrong? What do you
> > > recommend and what do you use yourself?
> > > 
> > > 
> > > Michael M. Joergensen
> > > Om Kaeret 4A
> > > DK- 2800 Lyngby
> > > http://g.co/maps/ff6pp
> -- 
>  Ing. Max Vittrup Jensen
>  "Jen-Sen: Make it Reality"
>  Consultancy in sustainable engineering, planning and environment
>  +420 585 15 20 10 - www.jen-sen.cz 
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