[GSBN] R value export straw blocks?

Enga Lokey enga at thelokeys.net
Sun Jan 25 02:44:09 CST 2015

Interesting timing on this thread as I was just at a local processing plant that makes these straw nuggets for export. Give me another couple of years and I might have some hard figures for you on U-values, but one question that came to mind immediately  was the buildability of these bales. Has anyone every tried to re-tie (resize) one to accommodate a real-world building scenario? The ones I saw were held together with 2 straps of highly tensioned tape in each direction. I don't yet have any on site to see how possible it would be to insert a bale needle or what happens when the straps are cut. It did appear that the straw was quite short and not consistently aligned (which could possibly be a good thing). 


enga at thelokeys.net

On 25/01/2015, at 5:18 PM, Kyle Holzhueter wrote:

> In Japan, compressed straw mats called Tatami are traditionally used for flooring in living- and bedrooms. Since the disposal of tatami mats has become an issue, we've begun using old tatami mats as infill insulation. There was an article about this in a recent issue of the last straw. My research studio has measured the thermal conductance/insulation value of a variety of Tatami mats using a KD2 Pro thermal properties analyzer, which basically involves sticking a pin into the substrate/insulation, a heat pulse is emitted and heat capacity, conductance etc. measured. Since tatami mats are designed to be used as flooring, they are generally denser than straw bales.  With some variation, unplastered straw tatami mats have a density of about 245kg/m3 and a thermal conductivity of about 0.116W/mK. Among tatami mats, the lower densities have lower thermal conductance. For example, a 217kg/m3 mat has a thermal conductivity of about 0.081W/mK, but this straw tatami mat has a 1.6mm layer of polystyrene foam in it's core.  For comparison, a Danish study regarding the U-value of straw bale walls systems which includes a chart outlining straw bale densities and thermal conductivity is available at the following link:
> http://www.homegrownhome.co.uk/pdfs/Danish%20english%20only.pdf
> A wild guess but I suspect the optimal density of straw in terms of thermal conductivity is between 100 and 150kg/m3. I'm speculating, but it seems that at greater densities, like we see in tatami mats, the straw is crushed reducing still air. Although a plastered straw bale per se would provide excellent insulation, I think the challenge with entire straw bale wall systems is eliminating air pockets in the wall that would enable convection.
> Kyle
> *************************************************
> Kyle Holzhueter  PhD (Bioresource Sciences), Research Associate
> Nihon University, Graduate School of Bioresource Sciences
> Architectural and Regional Ecological Design Studio
> 1866 Kameino Fujisawa Kanagawa 252-0880 Japan
> カイル・ホルツヒューター 博士(生物資源科学) 研究員
> 日本大学大学院 生物資源科学研究科                       
> 建築・地域共生デザイン研究室                    
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