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RE: GSBN:CalifoRnian values (was re: from the Crest list)

I like Derek's explanation a lot, partly cause it is true, and partly
because it deals properly with peoples preconceptions.
I like screwing people up by adding that SB walls have the potential to
be very airtight which is good for saving energy and improving help.
People get the idea that "breathable" means air goes through SB -- lets
hope not!

John Straube
Dept of Civil Engineering and School of Architecture
University of Waterloo
Waterloo, Canada

-----Original Message-----
From: GSBN [mailto:GSBN@...] On Behalf Of Derek Roff
Sent: May 11, 2003 19:44
Subject: RE: GSBN:CalifoRnian values (was re: from the Crest list)

> The difference between R-30 and
> R-45 means the difference between 0.033 Btu/hr/SF/F and 0.022 
> Btu/hr/SF/F. Repeat after me, "It just doesn't matter!  It just 
> doesn't matter."  I suggest we move on to other, more meaningful 
> disagreements.
> Nehemiah

In terms of a functioning house, I agree with Nehemiah that the exact 
R-value for SB doesn't matter.  I also like the statement that I 
first heard from Danny Buck of Living Structures:  The R-value of a 
strawbale wall is "enough."

When it comes to educating the public about strawbale building, I 
feel a need to say more.  What I say these days is something like, "A 
straw bale has a R-value of 45 or 50.  A well-built wall can have an 
R-value of 30 for the entire wall, according to tests done at Oak 
Ridge National Laboratories.  Fiberglass batts for 2 x 6 framing are 
rated at R-19 for the material, so that's less than half of the value 
for a straw bale.  Oak Ridge tested frame walls insulated with 
fiberglass batts, and measured R-values from a little over R-7 to 
R-12.  As with the raw materials, a fiberglass-insulated frame wall 
will yield less than half the insulative value of a strawbale wall."

I haven't figured out a way to say it more concisely, and still 
convey the needed information.  Plenty of people have come up to me 
and said, "I hear that strawbales are only R-30.  Since fiberglass is 
R-19, why should I bother with bales?"  I think it takes a bit of 
explanation to clarify the fallacies in that kind of statement.


Derek Roff
Language Learning Center, MSC03-2100
Ortega Hall Rm 129, 1 University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek@...