[GSBN] The Straw Stuff

Tue Mar 8 19:15:07 UTC 2011

For the same reason as Chris (slow drying of straw-clay that I had put 
in place) I have I experimented something last summer that is a little 
similar to Chris' 'Straw Stuff'. Its purpouse is to insulate, from the 
inside, a stone wall in my new 200 year old home. I don't remember if I 
told you allready that Coralie and I are splitting up and selling our SB 
house next week; time to move on...

I placed 3x4cm uprights spaced every 50cm and some 20 cm away from the 2 
meter high wall. Then  60cm high boards are screwed on and the cavity 
filled, just like straw-clay, but with loose straw. On that a 3x4cm 
batten was layed and a little higher we fixed a second batten.
We compressed the straw with carjacks placed between the 2 battens. Once 
we achieved serious resistance from the straw we took of the boards, 
fixed the lower batten (by screwing it unto the uprights), and took away 
the upper batten. Then the boards got fixed again (but higher) and the 
whole thing was repeated about 7 times. With the ceiling already there, 
it was impossible to go all the way up to the top of the wall.
The very sientific way of veryfing the obtained density was 'pushing on 
it with my hands' (feels just like a sturdy bale).
And the limit of compression we decided on was that we didn't like the 
uprights to buldge (the stone wall on the other side obviously didn't).
We shaved the straw, and earth plasered it. A section that has not yet 
been plastered since october has not bulged. I was afraid it might.
I intend to fill the top with salvaged woodfiber insulation mats, 
plaster what hasn't yet been covered, place an air barrier paper, more 
uprights and make it all look good with wooded siding. I could also just 
plaster it all (and cover the battens) but all the other walls are 
plasterd and I also like wood.

I know there might be a risk of condensation against the (cold) stone 
wall, but just wanted to try it anyway (only one way to be sure eh?). 
Figuring our climate is not very rude, the wall is south facing and made 
of pourous limestone/earth mortar I figured I might get away with it and 
this facade is simply too good looking to be insulated from the outside.

So far I'm happy with the result but I found the technique to slow to be 
able to work in a commercial context and would not dare advice it to 
anyone because of the potential condensation on the cold stone wall.

I'm surprised Chis, that you managed to keep a good density just by 
pushing it in by hand. So far I have not been able to get loose straw to 
stay under compression without something holding it down constantly. 
Chris, is the lath holding it in place?

I'm not really worried about fire (my kids are too young to smoke) but 
maybe I should (I have dutch friends).
Yet in that case, so should all those who use their bales on edge no? 
And when I work with bales on edge, and cut the twines while shaving the 
walls, to the great deception of my workshop participants, nothing 
happens...

Andre - not bulging an inch - de Bouter

Le 08/03/2011 17:52, Derek Roff a écrit :
> Like Bruce and Chug, I have some concern about increased fire risk. 
> However, it seems likely that if you have stuffed the straw to the 
> same density as a bale, then your fire resistance should be similar.  
> With the caveat that Bruce mentioned, of conditions changing 
> dramatically if/when the lath burns and allows the straw to 
> decompress.  I'm not sure that it would suddenly decompress, but it 
> might.
>
> It would be interesting to build a test wall section, leave it for a 
> couple of months, and then cut through the lathes.  That would give 
> some idea of whether the straw would acquire a compression set and be 
> fairly stable in its packed form, or whether it would still be eager 
> to unpack itself.
>
> I'd like to hear more about how you determined the density of the 
> stuffed straw.  I'm guessing that you found you could pack a bale of 
> straw into less than a bale's volume in the wall.  Is that right? 
> Chris, do you have any sense of how consistent the density was/is from 
> edge to edge and top to bottom?  I would have imagined that the lathe 
> would bow outward significantly, under the pressure necessary to reach 
> bale densities.  If I understand your posting correctly, that didn't 
> happen.
>
> How would you compare cost and time for stuffing straw in this way to 
> filling a similar wall cavity with dense-pack cellulose?  "The Straw 
> Stuff" is a very interesting experiment, and I'm glad that you shared 
> your information with us.
>
> Derelict
>
> Derek Roff
> Language Learning Center
> Ortega Hall 129, MSC03-2100
> University of New Mexico
> Albuquerque, NM 87131-0001
> 505/277-7368, fax 505/277-3885
> Internet: derek at unm.edu
>
> On Mar 5, 2011, at 9:16 PM, Chris Magwood wrote:
>
>> Hey all,
>>
>> This past summer, we did a little experiment with our students that
>> seemed to work well, and I'm curious if anybody has tried it (or has
>> good reason to not try it!) before I go ahead and try it on a
>> slightly larger scale.
>>
>> We were building two walls with straw/clay, using a double stud
>> framing system and using thin wood lath on the studs as the form/
>> cage for the straw/clay. We then used clay plaster over the lath on
>> the inside and outside. As usual in our climate, we were under the
>> gun to get the straw/clay placed in time for it to dry thoroughly
>> before plastering.
>>
>> As we were doing so, I wondered if we might just use the same
>> framing and lath system and stuff the cavity with dry straw instead
>> slip-straw. So we built a sample frame and did just that. The wall
>> was 12-inches deep (as was the straw/clay wall). We placed about 18-
>> inches of lath at a time and then packed in the dry straw. We
>> measured the density of the original bale and we were able to get
>> the straw into the wall cavity at a slightly higher density than the
>> bale itself. We had pieces of lath cut to go across the wall to keep
>> the straw packed down at the intended density, but found we really
>> didn't need them. The whole thing went together really, really
>> quickly and plastered up nicely.
>>
>> So can anybody think of a reason why this might not be a good idea?
>> Yes, I know it's not as fun and natural as stacking bales... I'm
>> still a huge fan of doing things that way. But so many people are
>> building stick frames of one kind or another and then going to all
>> kinds lengths to notch, trim and otherwise jam bales into those
>> frames. This system fits a double frame wall really well, accepts
>> plasters really well and in general seems like a decent way to go
>> about using straw as an insulation. The thickness can be varied to
>> reach intended insulation values.
>>
>> Thoughts?...
>>
>> Chris
>
> _______________________________________________
> GSBN mailing list
> GSBN at greenbuilder.com
> http://greenbuilder.com/mailman/listinfo/GSBN
>
>
> -----
> Aucun virus trouve dans ce message.
> Analyse effectuee par AVG - www.avg.fr
> Version: 10.0.1204 / Base de donnees virale: 1497/3491 - Date: 08/03/2011
>
>