[Strawbale] compressing or not

[Tom Peeters]

Hi Herbert,

I know the differences in U-value and I know the insulation depends on the weight of the bale, but I was referring to the extra comprenssion when placed in a wall: are there tests that show a significant change in U-value - for the better or the worse - when there is an extra compression of the bales in the wall?
I ask this because the insulation value from a bale comes - at least partly - from the air that is contained in the hollow straws, so I wonder if (to much) compression wouldnt squash the hollow straws and thus make the bales insulate less?

kind regards
Tom



On Wednesday, March 12, 2014 12:01 PM, asbn <asbn at baubiologie.at> wrote:
 
Dear Tom and Stefano

Yes there are tests for different weights, and lambda depends on the compression.
GrAT (TU Vienna) as well as Waldland made series of tests, showing that the ideal weight for a good insulation-value 
lies between 90 and 120 kg/m3.
For a standard small bale this means divided by 7,6, so a small bale should weigh between 12 and 15 kg.
Other way to find out if the bale is usable: if you can easily move the 2 strings together, it is too floppy.

And there is a different insulation-value for
bales on edge: lambda = 0,05(2)
bales laid flat: lambda = 0,085

As mainly bales laid flat are compressed (like in loadbearing construction), 
these walls have - although compressed - a worse thermal performance (U-value) than bales on edge,
which are normally used in infill-construction-systems. 


all the best
Herbert Gruber
-----------------
asbn - austrian strawbale network
3720 Ravelsbach, Baierdorf 6
Tel. 02958-83640
asbn at baubiologie.at
www.baubiologie.at



Am 12.03.2014 um 11:27 schrieb permacultura la boa:

I do not know if is there any 'scientific' test, I have only to share my experience: ten years practicing & teaching and 46 sb building realized.
>Tests many times are contradictory and often fail when they want to put natural materials into a table...
>stefano
>
>
>
>
>
>________________________________
>Date: Wed, 12 Mar 2014 03:01:46 -0700
>From: tompeeters13 at yahoo.com
>Subject: Re: [Strawbale] compressing or not
>To: casadipaglia at hotmail.com; jure.pozar at gmail.com; strawbale at amper.ped.muni.cz
>
>
>Are there scientific tests that show that compressing a wall actually benefits the insulation value or that provide a maximum compression level?
>
>
>kind regards 
>Tom Peeters
>
>
>
>On Wednesday, March 12, 2014 10:06 AM, permacultura la boa <casadipaglia at hotmail.com> wrote:
>
>From my personal experience, both in load bearing than in post and beam, compression (and well done!) is essential for static, structural and insulation reasons.
>Stefano
>www.laboa.org
>
>
>
>________________________________
>Date: Tue, 11 Mar 2014 12:59:56 +0100
>From: jure.pozar at gmail.com
>To: strawbale at amper.ped.muni.cz
>Subject: [Strawbale] compressing or not
>
>Dear all,
>
>I have a fairly simple question? Is it necessarily to compress a wall of strawbales which is supporting only itself. It is basicaly an exterior strawbale wrapper of an existing brick wall. As far as I can remember Kuba didn`t compress strawbales on his workshop on ESBG in 2011. Can the strawbales sit-down after some years due to its weight and make cracks to the exterior clay plaster? The height of the wall is less than 3 meters.
>
>Cheers 
>
>Jure
>
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