Re: SB: [Fwd from RT:] SB Vault Questions

[Marcus Hardwick <marcus1@sonic.net>]

Hi Doug,

I'm curious as to how you intend to "repackage" the straw bales to make them
tapered. If it helps you at all - the State of California Guidelines to Straw
Bale Construction requires the bale density in load bearing walls be a "minimum
calculated dry density of 7.0 pounds per cubic foot".

As for making them denser, at some point one needs to consider the change in
insulative properties that would occur, if that quality is to be retained, in a
wall/arch assembly. Also there would be a handling issue as, for example, 
a current three string rice straw building quality bale runs about 80-85 pounds
which is approximately 8 pounds per cubic foot (reduced to dry weight assuming
an equilibrium moisture content of around 10%). Double the density and you start
to need equipment just to handle the bales. 

Make the bales very dense and also small plus tapered..? 
Well, perhaps you could consider adobe? Clay is a low embodied energy material
that is abundant in many areas of the world. High thermal mass although not much
insulation.

I'm intrigued by the idea of geotexiles and think they could be used
(sparingly)  in conjunction with earth plastered straw bale for adding strength
in high seismic areas. How to fasten at foundation and roof plus detailing of
window and door openings need careful consideration. Using drainage type
geoplastic on the outside bale surface is an interesting idea although I'm not
sure it wouldn't set up a bit of a fire chimney.

How to life cycle cost effectively weather protect straw bale arch assemblies
seems to be the holy grail of SBC. Most of the arch testing I've heard of has
been pretty informal. Lots of room here for thesis areas for under grads if you
know any who are looking to go a bit outside the box (so to speak). Keep on the
quest.

Regards,
Marcus


> 
> ------- Start of forwarded message -------
> From: Doug  Nuttall <dnuttall@rcii.com>
> To: "'archilogic@yahoo.ca'" <archilogic@yahoo.ca>
> Subject: Fwd: More curiosity about straw bales
> Date: 11/22/02 11:31:12 AM

<snipped>
> I want to do an arch that has tapered bales, so there is no
> plaster between the bales, and use pure tension on the outside, pure
> compression on the inside, just to keep it simple.  Get the angles right,
> and the whole thing should work well.
<snip>

> I'm also looking for a relationship between bale density, compressive
> strength, and modulus of elasticity.  I'm pretty sure they should have
> that at CMHC, but I haven't spent enough time there to find what I'm
> looking for.  What I want is a relationship that will predict long term 
> performance of bales, and how it would change if I re-packed them to make them
> denser.

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