[GSBN] The Straw Stuff

[Bruce King]

I don't think anyone has replied to Chris' post (have you?).  I don't  
have much to add, other than the almost obvious concern about fire --  
you're describing a monolithic bale wall (no strings, no bales, just  
compressed straw).  A failure of the plaster/lath in a fire could  
release the packed straw, as has happened in bale structures when the  
strings were exposed and meltable, which would then feed dry straw to  
the flames.  A major bummer, as we say in California.

On the other hand you are neatly avoiding the well-known problem of  
moldy straw-clay, which happens even in our dry western climates;   
it's hard to fully dry out a mass of wet straw-clay.

You have greatly reduced one risk (mold) while increasing another  
(fire), and simplified your labor cost/time.  I'm not sure that even  
this august group has collectively enough data points to properly  
evaluate how much you changed either risk, or whether that's a worthy  
tradeoff.  I guess I'm inclined to say go for it -- pack that dry straw!

Thanks,

Bruce King, PE
Director of EBNet
Ecological Building Network
the art and science of building well
bruce at ecobuildnetwork.org
PO Box 6397
San Rafael, CA 94903 USA
(415) 987-7271
follow us on Twitter: @EBNetwork

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
>
> -- 
> www.chrismagwood.ca
>
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