[GSBN] R value export straw blocks?

martin hammer mfhammer at pacbell.net
Mon Jan 26 20:12:14 CST 2015

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 . . .


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).
> 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 Martin¹s 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 don¹t 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 Peter¹s 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 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 tested).
>>>>> 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.
>>>>> 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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> John F Straube
> jfstraube at uwaterloo.ca
> www.JohnStraube.com
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