[GSBN] R value export straw blocks?

John Straube jfstraube at uwaterloo.ca
Mon Jan 26 20:50:26 CST 2015


I do think the density is near its optimum if it is as high as 6 to 9 pcf.  
A tightly controlled test of conductivity for a sample of straw at 5 pcf, 1” thick (I am skeptical because of this) was measured to be 0.041 W/mK with some other measurements in the range of 0.04 to 0.55 W/mk (R3.6 to R2.6/inch).  The higher density rice straw performs more poorly as it often higher density (10 pcf, 160 kg/m3).
The problem with 5 pcf bales is that they are good for insulation but not really for plastering. So I think builders prefer denser stiffer bales and so the R-value of 2 to 2.5 is about the best we can expect for stiff strong SB.  But loosey goosey straw bales over R3 is likely quite achievable and ready-to-burst into flames fluffed up straw run through a hammer mill to reduce fiber diameter is more likely to be closing in on R4
But this is a lit review with a bias towards tightly controlled measurements.
I supposed I could do a C518 test of a few flakes of straw up to 4” thick (our current and the most common machine out there), but I really am interested in seeing a full bale done ….

On Jan 26, 2015, at 9:12 PM, martin hammer <mfhammer at pacbell.net> wrote:

> Very revealing graph John. Thank you. 
> 
> With the optimal density of most materials being in the 2 to 8 pcf range (for highest thermal resistance) this implies that the typical straw bale (in the 6.5 – 9 pcf range) is already at or near its optimal density. Any thoughts?  Also, I wonder about a straw bale filled with freon or argon.  Hmmm . . .
> 
> Martin
> 
> 
> On 1/26/15 4:25 PM, "John Straube" <jfstraube at uwaterloo.ca> wrote:
> 
>> I am not sure if I can send images but I am trying 
>> If you are at high density (soil, wood etc), then reducing density increases R-value (that is decreases thermal conductivity). If you are at very low density, then decreasing density decreases R-value
>> The plot below is made up of many many materials.
>> The vertical axis is conductivity and the horizontal axis is density.
>> You can see the lowest conductivity / highest R-value per inch, occurs around 30 to about 125 kg/m3.  (2 to 8 pcf). The obvious deviation around 30-40 kg/m3 (2-2.5 pcf) is due to foams filled with gases other than air (Freon etc).
>> 
>> 
>> <image.jpg>
>> On Jan 26, 2015, at 3:35 PM, Graeme North <graeme at ecodesign.co.nz> wrote:
>> 
>>> thanks John - I knew that there were at least some research answers out there.
>>> Reminds me once again how lucky we are to have such wonderful researchers and scientists contributing so willingly to this group.
>>> 
>>> Graeme
>>> 
>>> 
>>> 
>>> On 27/01/2015, at 9:06 AM, 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> 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
>>>>> 
>>>>> <BWL logo for email.jpg>
>>>>> 
>>>>>> On Jan 24, 2015, at 3:12 PM, martin hammer <mfhammer at pacbell.net> wrote:
>>>>>> 
>>>>>> 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 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
>>>>>> 
>>>>>> 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> 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> 
>>>>>>> 
>>>>>>> _______________________________________________
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>>>>>>> GSBN at sustainablesources.com
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>> 
>> John F Straube
>> jfstraube at uwaterloo.ca
>> www.JohnStraube.com
>> 
>> 
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John F Straube
jfstraube at uwaterloo.ca
www.JohnStraube.com






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