[GSBN] R value export straw blocks?

Kyle Holzhueter nihondaigaku.kairu at gmail.com
Sun Jan 25 00:18:45 CST 2015

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:
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 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
〒252-0880 神奈川県藤沢市亀井野1866

TEL/FAX: 0466-84-3364
Mobile: 080-3477-9841
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