[GSBN] R value export straw blocks?

Andrew Thomson ab3ajt at bath.ac.uk
Tue Jan 27 06:53:20 CST 2015


It is also perhaps worth noting that Stramit panels (according to their 
data http://www.stramit.co.uk/content/view/13/30/) have a standard 
density of 350kg/m3 and a thermal conductivity of 0.102 W/mk 
(R=0.5882m^2 kW for 58mm thick panel).

Andy

Dr Andrew Thomson MEng PhD
BRE Centre for Innovative Construction Materials
Dept of Architecture and Civil Engineering
University of Bath

01225 386621


On 27/01/2015 12:31, Andrew Thomson wrote:
> Hi All,
>
> I have recently joined as a posting member to GSBN so thought I'd add 
> to the conversation on thermal conductivity of straw at different 
> densities. Colleagues of mine at the University of Bath have done some 
> testing in this area and published the findings - details here: 
> http://opus.bath.ac.uk/30137/
>
> The paper includes a graph (copied below) of tests done at Bath Uni 
> and others, including FASBA. The results suggest that below a density 
> of 120kg/m3 thermal conductivity is less sensitive to deceasing 
> density than might be expected. It appears that the thermal 
> conductivity of straw is actually more sensitive to the temperature of 
> the straw and it's moisture content. Hope this is of interest.
>
> Cheers, Andy
>
>
>
> Dr Andrew Thomson MEng PhD
> BRE Centre for Innovative Construction Materials
> Dept of Architecture and Civil Engineering
> University of Bath
>
> 01225 386621
>
> On 27/01/2015 00:25, John Straube 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 
>> <mailto: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 
>>> <mailto: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>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> GSBN mailing list
>>>>>>> GSBN at sustainablesources.com
>>>>>>> http://sustainablesources.com/mailman/listinfo.cgi/GSBN
>>>>>> <StakBlockFacts.png><StakBlockR-Value.png>_______________________________________________
>>>>>> GSBN mailing list
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>>>>>
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>>
>> John F Straube
>> jfstraube at uwaterloo.ca <mailto:jfstraube at uwaterloo.ca>
>> www.JohnStraube.com
>>
>>
>>
>>
>>
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