[GSBN] R value export straw blocks?
Andrew Thomson
ab3ajt at bath.ac.uk
Tue Jan 27 12:53:20 UTC 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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