[GSBN] R-values for cob, ideally documented

[Martin Hammer]

Hi Art,

Off list I will forward documents on this subject (from UK and Australia)
that were provided to me by John Fordice of the Cob Research Institute
(CRI). I¹m planning to use them as the basis for the thermal performance
(thermal resistance and mass properties) for our cob code proposal. But with
the review of Nehemiah Stone who is expert on thermal resistance and
testing. He plans to first assess them for credibility at the end of May.

Nehemiah was instrumental in establishing the still-used R-value for straw
bale walls for California while he worked at the California Energy
Commission in the mid-nineties. I believe he is on the GSBN.

I didn¹t hear R 1.25 per inch at the West Coast Natural Building Conference,
but I¹m highly skeptical. I¹m even skeptical of R-0.8.

By comparison, the R-values Nehemiah and I settled on for straw bale walls
in IRC Appendix S, based on the most reliable testing in the US, Denmark and
the UK, are R-1.55/inch for bales laid flat and R-1.85/inch for bales
on-edge. The values settled on for light straw-clay in IRC Appendix S by me,
Paula Baker-Laporte and others on our LSC code team range from R-1.8/inch
for density of 10 pcf, to R-0.84/inch for density of 50 pcf. As I remember,
these are based on a USDA Forest Products Lab report, a testing report by
the Canada Mortgage Housing Corporation and studies by research scientist
Douglas Piltingsrud.

Cob density is always well above 50 pcf, and therefore should have a thermal
resistance significantly less than R-.84 (if you trust the LSC values).

Martin Hammer


From:  Gsbn <gsbn-bounces at sustainablesources.com> on behalf of Art Ludwig
<oasis at oasisdesign.net>
Reply-To:  GSBN <GSBN at SustainableSources.com>
Date:  Tuesday, May 1, 2018 at 6:11 PM
To:  GSBN <GSBN at SustainableSources.com>
Subject:  [GSBN] R-values for cob, ideally documented

Hello people‹

I am working on getting our cob structures to pass Title 24 California
Energy Efficiency requirements. Got this from Gord Baird:

> static heat flow of R 0.8 per inch, and a dynamic heat flow of R 2.0 per inch.

Anyone else have anything to contribute on the topic of R-values for cob? R
1.25 per inch was mentioned at the West Coast Natural Building Conference...

The % of straw made an obvious difference in insulation value when we did
fire resistance testing, but we did not translate this to an R-value. We
could have up to 50% straw by volume in the mix (a bucket of loose straw per
bucket of sand+clay).


Gord¹s $0.02:
> The R22 to  R24 was full the whole  house actual performanceŠ but we had some
> walls at a steady state condition, and others in a dynamic condition.
> There are two equally important numbers  a static heat flow of R 0.8 per inch,
> and a dynamic heat flow of R 2.0 per inch.
> 
> Steady State:  Assuming that there is no sun then cob will act at r 0.8 (with
> pumice or without).   We had hoped the pumice would be more influential for
> insulation, but all it really provided was an additional R 0.2 over and above
> regular cob.  It did provide a 2 fold increase in compression strength.    Any
> cob wall in cloudy climates or north or shaded locations will act as a steady
> state performance -  our home the North wall acted like the steady state
> value.  We had hoped the pumice would be more influential for insulation, but
> all it really provided was an additional R 0.2 over and above regular cob.
> 
> Dynamic State:  On the south wall, our 24 inch walls acted like R 40 due to
> the ability to readily accept and store the solar radiationŠ cob has a slower
> thermal radiation which means that even in colder climates like ours that the
> south wall is fairly useful as it can collect more energy than it can radiate
> it away.     
> 
> Some of it is covered in this document
> https://ecosenseliving.files.wordpress.com/2011/09/science-research-report_sep
> t_1.pdf    
> 
> A coincidence to get your email todayŠ I had someone want to speak to me about
> greywaterŠ and they were from Los Angeles.   I sent them your way.    I recall
> you were moving (or  planning) on heading to the San Fran Bay area.
> Cheers
> Gord Baird
> gord at eco-sense.ca
> www.eco-sense.ca <https://eco-sense.ca/>
> 
> 3295 Compton Rd.
> Victoria, BC, V9E 1C8
> Phn: 250-478-2680

_______________________________________________ Gsbn mailing list
Gsbn at sustainablesources.com
http://sustainablesources.com/mailman/listinfo.cgi/gsbn

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.sustainablesources.com/pipermail/gsbn/attachments/20180505/77c34bbe/attachment.htm>