[GSBN] R value export straw blocks?

Bruce EBNet bruce at ecobuildnetwork.org
Mon Jan 26 14:27:49 CST 2015


Graeme (et al) —

Be sure to read John Straube’s extensive reply on this thread, like “Cellulose, rockwool, fiberglass and expanded polystyrene all increase their R-value as density increases from very low levels All have an optimal point, which varies slightly, and then the R-value drops again.”.

John surely knows more than I, but it’s easy to imagine that a per-inch R-value for an insulation material will be a function of several things, such as:
- the conductance of the material itself (as opposed to the fluffy insulation product), e.g., the solid wall of the straw vs. a tube-shaped single straw vs. a straw bale — three very different things
- the size of the captured air pockets:
	- how much do they vary?
	- how much do they interconnect?
	- what is the average size? ( can there be convection cycles within them?
	- and probably other things

Everybody make a mental note:  the next time some student asks what straw bale subject needs further research, this is it:  what is optimal density for optimal thermal resistance?

Thanks,

Bruce King

(415) 987-7271
BuildWellLibrary.org



> On Jan 26, 2015, at 12:06 PM, Graeme North <graeme at ecodesign.co.nz> wrote:
> 
> Bruce
> 
> Interesting
> 
> My observation of R values of different materials over many years , (esp with earthen materials  mixed with  aggregates of different densities ranging from stone to straw), generally points to an almost linear and direct inverse correlation between density and R value, whereby R value increases as density decreases - so am a bit puzzled by this discussion
> Unless the  k value for straw is significantly better than that of still air?
> And is there really any significant convective flow of air within a straw bale, plastered or not? 
> Has anyone got any figures?
> 
> More questions than answers
> 
> 
> Graeme    
> 
> 
> On 25/01/2015, at 12:43 PM, Bruce EBNet <bruce at ecobuildnetwork.org <mailto:bruce at ecobuildnetwork.org>> wrote:
> 
>> 
>> Let me jump right in with a couple of things to add to Martin’s post:
>> 
>> 1)  I have been a board member and partial owner of Stak Block for ten years, so speak with a bit of certainty when I basically agree with Martin;  the thermal tests were a bit funky (an undergrad engineering student doing his first unguarded hot plate test at Cal Polytechnic University in California).  I emphatically agree that we don’t know, and would like to know, the optimal density of a straw bale (or block) for insulating purposes.  My gut sense is that it will be denser than conventional bales, maybe even as dense as Peter’s super-compressed bales.
>> 
>> 2)  The widely-accepted R-values Martin quotes are averaged values taken across a plastered bale section, including the thickness of plaster.  A plastered straw bale wall is an intricate composite assembly that achieves far better structural, fire and thermal properties than the sum of its constituent parts.  That is, a straw bale by itself probably has much less than R1.3 or 2 as described because there is no plaster to arrest convective air flow across the assembly.
>> 
>> 3)  When we ran the straw bale research program 14 years ago we did look at super compressed bales, but only glancingly.  If someone contemplates using them in a building, they should consider not only R-value, but also bond of plaster to the face of straw (is it better?  worse?).
>> 
>> cheers everyone,
>> 
>> Bruce King
>> 
>> (415) 987-7271
>> BuildWellLibrary.org <http://buildwelllibrary.org/>
>> <BWL logo for email.jpg>
>> 
>>> On Jan 24, 2015, at 3:12 PM, martin hammer <mfhammer at pacbell.net <mailto:mfhammer at pacbell.net>> wrote:
>>> 
>>> Hello Lance,
>>> 
>>> A delayed reply on this.
>>> 
>>> A company in California called Oryzatech (http://www.oryzatech.com/ <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 I’m skeptical of the R-value claim because I haven’t seen a bona fide testing report, and it’s 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 tested). 
>>> 
>>> Though counterintuitive, it’s 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 1’x1’x2’ blocks weigh 30 pounds. So they are 15 pcf or 240 kg/m3. Peter’s 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 I’m stating for a typical straw bale and for a Stak Block, I don’t know how you would reliably extrapolate them to a denser block. The obvious answer is to subject Peter’s 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 <x-msg://111/d2bdesign@gmail.com>
>>> 
>>> Speaking of Peter, was he ever seconded and brought into GSBN?
>>> 
>>> I hope this is helpful.
>>> 
>>> Best.
>>> 
>>> Martin
>>> 
>>> 
>>> Martin Hammer, Architect
>>> 1348 Hopkins St.
>>> Berkeley, CA  94702
>>> 
>>> 
>>> On 1/1/15 7:41 PM, "Lance Kairl" <sabale at bigpond.com <x-msg://111/sabale@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 <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> 
>>>> 
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