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RE: GSBN:Re: Question re R-values


I would be careful about quoting the Sandia Labs' report.  It had some
serious limitations.  Also, be careful with interpretations of ORNL's
tests.  ORNL has develoed a term they call "effective R-value."  While it
does do a better job of accounting for extra lumber in the wall and the
lost insulation value of spaces left unisulated, it unfortunately also
mixes infiltration with thermal conductance - what the R-value is supposed
to measure.

However, you are right that a simple comparison of fiberglass' R-19 to
straw bales' R-30 (or R-33) is not appropriate either.  Recent research
sponsored by the Energy Commission indicated that an "R-19 wall" as it is
generally constructed, only gives about R-12.  If extra care is taken to
make sure that insulation surfaces are flush to siding and sheetrock
surfaces, that insulation surrounds all wiring, that it fits tight around
switch and outlet boxes, and that it completely fills all bays, then the
"R-19" insulation will give you about R-14.  Whoopee!

On the whole, I agree with your approach of avoiding the simplistic answer.
However, I have also found that some people are more than a little turned
off by a technical answer to what they thought was a simple question.


> [Original Message]
> From: Derek Roff derek@...
> To: GSBN GSBN@...
> Date: 12/29/2004 12:27:06 PM
> Subject: GSBN:Re: Question re R-values
> I think it is risky to pretend that a complex issue is simple, to satisfy
> momentary need.  In talking with clients, enthusiasts, code officials and
> the curious, I am constantly bemused by the mis-application of
> and the incorrect analysis and extension of data.  At a minimum, I feel it
> is essential to quote a source for any simplification, as Bob did below.
> Most people that I talk to are mentally comparing strawbale to the myths
> the US insulation grail, R-19 fiberglass batts.  If I say that strawbale
> has an R-value of thirty, many people conclude that it is just a little
> better than fiberglass.  I prefer to say that strawbale as a building
> component has an R-value of 50, according to tests at Sandia National
> Laboratories tests.  I compare this to the R-19 fiberglass that they are
> familiar with.  Next I say that a well-built SB wall will have an R-value
> of around 30, according to Oak Ridge National Laboratory (ORNL) tests.  I
> compare this with the ORNL ratings of R-7 to R-11 for a wall insulated
> nominal R-19 fiberglass.
> I find that most people have never considered the possibility that R-19
> fiberglass doesn't guarantee an R-19 wall.  However, they can understand
> and accept the concept that a whole wall will have a lower average
> insulation value than its most insulating component.  I also mention that
> poorly built wall, whether insulated with SB, fiberglass, or anything
> can have a much lower insulation value.
> This is the simplest way to answer the R-value question that I have found,
> while still being effective in conveying some of the essential
> and providing a fairly accurate basis for comparison.
> Derek
> Derek Roff
> Language Learning Center
> Ortega Hall 129, MSC03-2100
> University of New Mexico
> Albuquerque, NM 87131-0001
> 505/277-7368, fax 505/277-3885
> Internet: derek@...
> --On Wednesday, December 29, 2004 10:10 AM -0800 Bob Bolles
> Bob@... wrote:
> > California Energy Commission has set Straw Bales at R-30, and that is
> > value we use.
> > bb
> >
> > Bob Bolles
> > Sustainable Building Systems
> > San Diego, CA - USA
> > Bob@...
> > www.StrawBaleHouse.com
> >
> > ----- Original Message -----
> > From: "Joyce Coppinger" jc10508@...
> > To: "GSBN" GSBN@...
> > Sent: Wednesday, December 29, 2004 10:04 AM
> > Subject: GSBN:Question re R-values
> >
> >
> >> When answering the question about R-values of bale walls and
buildings, I
> >> usually use a range rather than a specific number. A request has come
> >> asking for a specific R-value to satisfy the building codes officials
> >> are reviewing a project in the Northwest USA.
> >>
> >> I'm wondering what answer you would give to this question?
> >>
> >> Joyce
> >>
> >> Joyce Coppinger
> >> Managing Editor/The Last Straw, the international quarterly journal of
> >> strawbale and natural building
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