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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>I would agree with aiming high on the exterior insul. I pay
about 17 cents per board foot of eps so it is not a big expense compared to the
labour of an renewing an exterior. <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>I have a project that I am having trouble making a decision
about the location of the drainage plane. It is 2x4 frame with eps infill and
3.5” of exterior eps. My original plan called for a 10mm drainage
plane between the wall ply sheathing and the insulation board similar to eifs
systems. The drain gap was planned as bottom drainage vent only and sealed
at the top, i.e. minimal venting. The disadvantage of the wall was a
reduction in the thermal value of the exterior insulation depending on air
movement (there will still be air movement). How much of a reduction is hard to
determine and I am wondering what other disadvantages there might be.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>The reason for the drainage plane at the sheathing is that the
foam is being covered with a render so didn’t require battens as a
nailing surface and I felt it is easier to detail penetrations at the sheathing
level with any potential moisture having a better opportunity for drying.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'>
<p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:
"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;
font-family:"Tahoma","sans-serif"'>
greenbuilding-bounces@lists.bioenergylists.org
[mailto:greenbuilding-bounces@lists.bioenergylists.org] <b>On Behalf Of </b>John
Straube<br>
<b>Sent:</b> March 21, 2011 4:15 PM<br>
<b>To:</b> Green Building<br>
<b>Subject:</b> Re: [Greenbuilding] exulation<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Adding insulation on the outside is a a great idea if you
are interesting in reducing heat loss and avoiding condensation.<o:p></o:p></p>
<div>
<p class=MsoNormal>The key to avoiding condensation is to use as high an
R-value on the exterior as possible, thereby warming the existing sheathing
temperature and hence reducing the chance of condensation. Placing enough
insulation outside the existing wall and condensation is practically
impossible.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
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<div>
<p class=MsoNormal>In your climate, given a 2x4 wall, even 1" of extruded
would be pretty safe, and will decrease heat flow by about 1/4. I would
try for R7.5 or so, and thus reduce heat flow to about 60% of what it was
before. Given that you get to do this type of retrofit once every 40-75
years, I would aim high with the R-value, and add R10 or more. XPS
(R5/inch) and polyiso (R6/inch) are good choices given their higher R-values
per inch, but EPS is fine and even Rockwool can work (R4 per inch for
both) <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>In all cases, I would try very hard to get as good an air
barrier as possible, and it is critical to get a good drainage plane.
Taping joints will do both, but some are concerned with the durability of
the tape. <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>Check out our website at <a href="http://buildingscience.com">buildingscience.com</a>
for case studies and details.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>In my own house with 2x4 framing, I added 4.5" of
ccSPF, and have no regrets. <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal> <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
<div>
<div>
<p class=MsoNormal>On 2011-03-21, at 2:54 PM, Chris Koehn wrote:<o:p></o:p></p>
</div>
<p class=MsoNormal><br>
<br>
<o:p></o:p></p>
<div>
<p class=MsoNormal>I am planning some work on a 1970's single storey home here
on Vancouver Island. Replacing windows is the impetus. The home has vertical
cedar channel siding over tar paper over sheathing (both ply and solid sawn
recycled form wood in different areas) over 2X4 framing with fiberglass batt
insulation, over 6 mil poly vapor barrier over GWB. We are in zone 4C,
"mixed marine" with roughly 5400 f HDD. Our heating season is long
but rarely severe. <<a
href="http://www.greenbuildingadvisor.com/sites/default/files/H-T%20Zones%20-%20legend.jpg">http://www.greenbuildingadvisor.com/sites/default/files/H-T%20Zones%20-%20legend.jpg</a>><o:p></o:p></p>
<div>
<p class=MsoNormal><o:p> </o:p></p>
<div>
<p class=MsoNormal>I'm considering removing exterior siding and adding a layer
of rigid insulation while I'm at it. Some siding needs to be removed anyway for
window replacement and some in other areas needs to be replaced due to flicker
damage, so taking it all off (and re-using it) doesn't seem to me to be a
substantial added burden. <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<div>
<p class=MsoNormal>Quoting the U.S. DOE site: "<span
class=apple-style-span><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:#3C4349'>Foam board insulation is commonly placed between the exterior
finish (i.e., siding, brick) and the studs of exterior walls. To prevent air
infiltration, you should place rigid insulation boards tightly together and
seal the seams with tape or caulk. However, this practice may worry some builders
in cold climates since the foam board may act as a second vapor diffusion
retarder. Studies have shown, however, that condensation rarely occurs in these
areas unless something else is seriously wrong with the wall assembly (i.e.,
massive uncontrolled air leakage into the walls from the house). If the
assembly is constructed correctly, the inside surface of the foam board stays
warm enough to keep water vapor in its gaseous state long enough for it to
escape."</span></span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>In the few areas I have opened the walls up I have seen no
evidence of condensation, though in some areas near the top plate some of the
insulation has turned grey, indicating air moving through it. It is possible, I
suppose, the air that's moving through the wall is not coming from the inside.<o:p></o:p></p>
</div>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>My questions to the group are:<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>* Given our climate and wall profile, is adding insulation
to the outside a good idea? <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>* Is there a type of insulation recommended for this work,
specifically in light of any concerns over moisture drive, as well as a desire
by the client to keep the thickness build-up minimal, and of course cost.<o:p></o:p></p>
</div>
</div>
<div>
<p class=MsoNormal>* What are suggestions around detailing: joints between
insulation panels, treatments at the bottom (siding currently laps directly
over brick, which is applied to a concrete foundation), fastening schedules
(insulation and siding), drainage plane. The house has min. 2' overhangs. <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>Thanks as always,<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>Chris Koehn<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>TimberGuides<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>Cobble Hill, BC<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
</div>
<p class=MsoNormal>_______________________________________________<br>
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<p class=MsoNormal><o:p> </o:p></p>
<div>
<div>
<div>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Helvetica","sans-serif";
color:black'>Dr John Straube, P.Eng.<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Helvetica","sans-serif";
color:black'>Associate Professor<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Helvetica","sans-serif";
color:black'>University of Waterloo<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Helvetica","sans-serif";
color:black'>Dept of Civil Eng. & School of Architecture<o:p></o:p></span></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:"Helvetica","sans-serif";
color:black'><a href="http://www.buildingscience.com">www.buildingscience.com</a><o:p></o:p></span></p>
</div>
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</div>
<p class=MsoNormal><o:p> </o:p></p>
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