[GSBN] R value export straw blocks?

martin hammer mfhammer at pacbell.net
Sat Jan 24 17:12:20 CST 2015

Hello Lance,

A delayed reply on this.

A company in California called Oryzatech (http://www.oryzatech.com/) has for
years been in the development of manufacturing a compressed straw block
called Stak Block (see attached fact sheet). They have made claims of an
R-value of 3.89/inch (see 2nd attachment). I like this product in many ways
and think it has tremendous potential. However I¹m skeptical of the R-value
claim because I haven¹t seen a bona fide testing report, and it¹s hard to
believe the R-value of a compressed straw block would double compared to a
typical straw bale.

The R-value for a straw bale, from the most trusted test in the US (the 1998
guarded hot-box test at Oak Ridge National Laboratory) is R 1.3/inch laid
flat and R-2/inch on-edge. This is still a matter of debate, but this is
what the testing showed. The difference in R-value per inch is explained by
the predominant orientation of the straw in a bale (or at least in the bales

Though counterintuitive, it¹s possible a compressed bale would have a higher
unit R-value than a normal bale, if by being compressed it confines more air
spaces. Thermal resistance is all about maximizing the number of confined
air spaces and reducing thermal bridging. Regarding the latter, I would
expect the thermal bridging across a bale would increase when it is
compressed. There is likely an optimum density for straw that will yield the
highest unit R-value, but this has yet to be researched and demonstrated.

Another point of thermal resistance comparison is polyiscocyanurate, which
has the highest unit R-value of any foam plastic insulation at R 5.6/inch.
For years polyiso claimed an R-value of 6.0/inch (or higher), but it was
adjusted downward a year ago under new testing protocol. (Sorry to bring a
distasteful petrochemical insulation into the discussion of natural
insulation! It does have quite an ability to insulate however.) Fiberglass
insulation is said to be R3.1 to R4/inch (material only, not including
thermal bridging of framing).

Regarding density, from the Stak Block fact sheet, the 1¹x1¹x2¹ blocks weigh
30 pounds. So they are 15 pcf or 240 kg/m3. Peter¹s compressed bales are 468
kg/m3. Those are quite dense, almost twice as dense as the Stak Blocks, and
4 times as dense as a typical straw bale. Even if you trust the R-values I¹m
stating for a typical straw bale and for a Stak Block, I don¹t know how you
would reliably extrapolate them to a denser block. The obvious answer is to
subject Peter¹s blocks to a reliable test.

You or Peter Torok might contact the co-founder of the company Stak Block to
better understand nature of their blocks and their tested thermal
resistance.  Ben Korman: d2bdesign at gmail.com

Speaking of Peter, was he ever seconded and brought into GSBN?

I hope this is helpful.



Martin Hammer, Architect
1348 Hopkins St.
Berkeley, CA  94702

On 1/1/15 7:41 PM, "Lance Kairl" <sabale at bigpond.com> wrote:

> Any one have  an idea on R value for super compressed export Bales.
> Any info will be passed on ,
> Although I should nominate Peter  to join the list.
> Is there a seconder out there, and then I will fill you in on his good works.
> Regards lance kairl
> Hosue of Bales.
> From: Peter Torok [mailto:torokenterprise at me.com]
> Sent: Thursday, 11 December 2014 1:13 PM
> To: House of Bales
> Subject: R value
> G'day lance, 
> As discussed these bales are very well compacted, the dimensions are
> 400x500x480 45kg or 400x500x240 22kg baled at less than 12% moisture and
> compressed at 5000 psi. If the bales were sitting on the 400 side, the straw
> runs horizontal. I inquired about lowering the pressure and he felt the
> integrity of the bale would be jeopardized, but more pressure can still be
> applied. I hope that is enough information to calculate a rough R value for
> both thickness', I look forward to hearing what you come up with. Thanks for
> helping me out with this, it's very much appreciated.
> I have found old studies from around 2003 that calculate between R1.4-2.4 US
> measure / inch
> This R1.4 ­ 2.4 relates to standard housing bales,
> Export ones may equate to the R value  for Timber??
> Regards Pete Torok
> Earth Wood & Straw
> 0411 304 794 <tel:0411%20304%20794>
> _______________________________________________
> GSBN mailing list
> GSBN at sustainablesources.com
> http://sustainablesources.com/mailman/listinfo.cgi/GSBN

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