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<DIV><FONT size=2 face=Arial>Janne,</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>R-values in the energy code tables are just for
insulation materials. The intent of the code when limiting U-factors is
that you include all layers of the entire assembly, and not just the
insulating materials. This is why the U-value requirement is very seldom
equal to 1/R. What you should do is add all R-values for the insulation,
skin materials on the wall, and the indoor and outdoor air film
coefficients. Then compute the U-value and see if it meets the 0.064
limit.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>I believe that most of the values presented in the
tables have already assumed certain bridging conditions, and that is
why (repeating what I said above) the R-values for insulation materials do
not usually match the inverse of the overall U-factors. You can see this
more clearly when you look at below grade walls. Since no air film would
be present, the insulation requirement is expressed as C. The value
C-0.119 inverted is R-8.4, whereas the R-value requirement is just R-7.5.
In this case, the remaining 0.9 R-value is assumed to be available from the
masonry wall. </FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Regards,</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>LOD </FONT> </DIV>
<DIV><FONT size=2 face=Arial>===========================<BR>Larry O. Degelman,
P.E.<BR>Professor Emeritus of Architecture<BR>Texas A&M University<BR><A
title="mailto:ldegelman@suddenlink.net
CTRL + Click to follow link"
href="mailto:ldegelman@suddenlink.net">ldegelman@suddenlink.net</A><BR>===========================</FONT></DIV>
<DIV style="FONT: 10pt Tahoma">
<DIV><BR></DIV>
<DIV style="BACKGROUND: #f5f5f5">
<DIV style="font-color: black"><B>From:</B> <A
title="mailto:JKairento@B2Qassociates.com
CTRL + Click to follow link"
href="mailto:JKairento@B2Qassociates.com">Janne Kairento</A> </DIV>
<DIV><B>Sent:</B> Wednesday, December 15, 2010 2:16 PM</DIV>
<DIV><B>To:</B> <A title=bldg-sim@lists.onebuilding.org
href="mailto:bldg-sim@lists.onebuilding.org">bldg-sim@lists.onebuilding.org</A>
</DIV>
<DIV><B>Subject:</B> [Bldg-sim] Mass. Energy Code</DIV></DIV></DIV>
<DIV><BR></DIV>
<DIV class=WordSection1>
<P class=MsoNormal>Hello!<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>For Climate Zone 5, IECC requires a minimum insulation value
of R-13 + R-7.5 c.i. for a steel framed building. If the studs are 16” on
center, the thermal bridging degrades the batt R-value of 13 down to an
effective R-6 c.i. which bring the total insulation value to R-13.5 c.i.
Currently, I am reviewing a building with 2.5” of R-5 extruded polystyrene total
an insulation value of R-12.5 c.i. However, the building wall assembly exceeds
the ‘Assembly Minimum’ of U-value 0.064. Since IECC 2009 is the effective energy
code of Massachusetts since June 30, 2010, is the insulation assembly in
agreement with the Minimum Envelope Requirements if the ‘Assembly Maximum’ is
exceeded? Any input will be much appreciated!<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: black">Regards,<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: black"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: black">Janne
Kairento</SPAN><o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><o:p> </o:p></P></DIV>
<P>
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