<html><head><base href="x-msg://828/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi All:<div><br></div><div>I located our report from the Real Goods project I mentioned a couple weeks back. Attached, with its appendices. It is based on post-occupancy performance data done by students at the University of California - Berkeley.</div><div><br></div><div>Jump to p. 4 for the straw-bale discussion, and also Appendix I. I note that the students needed a guess at an assumed R value in order to generate a predicted set of core temperatures, and then used actual data to somewhat confirm it. That does not fully justify that the walls have an actual R<i>us</i>-value of 65 (R<i>si</i>-11.44) [U<i>us</i>-value of .015 (U<i>si</i>-0.087)] but I do suspect that it's somewhere approaching that. </div><div><br></div><div>Again, these walls have 23" (584mm) 3-string rice straw bales, laid flat, with ±3" (76mm) of PISE (earth-cement) on the interior and ±4" (102mm) on the exterior. </div><div><br></div><div>Permit me to be the first to say that this is not the most scientific study.</div><div><br></div><div>If I recall correctly, when the State of California tested bale a bale wall panel for R-Value, the sample wall was still wet, and tested to R<i>us</i>-value of 33 (R<i>si</i>-5.81). Here I suspect the actual value is higher, and probably would've been had the plaster and bales been more dry. But as a result the California Energy Commission assigned an assumed R<i>us</i>-value of 30 (R<i>si</i>-5.28) for bales laid both flat or on edge. That's the value we still use today.</div><div><br></div><div>So, while perhaps not truly tested, it is safe to say bale walls have thermal performance values that fall somewhere between 'impressive' and 'stunning'.</div><div><br></div><div>Cheers,</div><div><br></div><div>David</div><div><br></div><div>ps: On the question of an exterior render—or not—behind a rain screen, for a lodge in Alaska we applied a thin coat of earth-cement plaster (sandy site soils mixed with cement), more due to concerns about keeping critters out than about air movement. There's a 1" (25mm) gap between the plaster and a loosely fitted log cull rain screen. While air movement within bales is very dependent upon the density, I have to agree with Danny's hypothesis that limiting of air movement with an exterior render greatly improves r-value. </div><div><br></div><div></div></body></html>