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<DIV><FONT size=4>I am wondering if it would be reasonable to install accurately
precut eps foam between joist, rafters, or top chord of truss during the framing
to achieve a cheap relatively tight installation when compared to fiberglass
with the air seal being achieve outside the framing with continuous 6” eps foam
managed for air tightness. More detailed description is below.
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<DIV><EM>From: John Straube </EM></DIV>
<DIV><EM>Sent: Wednesday, November 28, 2012 1:13 PM </EM></DIV>
<DIV><EM></EM> </DIV>
<DIV><EM>Experience has taught those who have built a few of these
externally-insulated buildings that they can be easier to build too. This
means one has to learn how to handle the remaining challenges</EM></DIV>
<DIV><EM>1. how to find low cost long screws that screw in quickly and
easily</EM></DIV>
<DIV><EM>2. the furring needed to allow for easy cladding fastening</EM></DIV>
<DIV><EM>3. the details at window and door openings required to mee</EM></DIV>
<DIV><EM>Point 3 is still evolving and improving.</EM></DIV>
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<DIV>My comments:</DIV>
<DIV>I am designing a house mounting eps on exterior of framing. I found a
source of eps that is a lower price than fiberglass/R. By making it on the
outside, I avoid the conflict with wires and plumbing commonly installed in the
framing and achieve continuity. Also, the framing is inside the
thermal envelope and therefore near the conditioned temp. I am addressing
the three issues John brought up. </DIV>
<DIV> </DIV>
<DIV>I found a source of long screws. </DIV>
<DIV><A
href="http://www.loghomestore.com/1748-headloc-panel-fasteners-9-to-18-inch.php">http://www.loghomestore.com/1748-headloc-panel-fasteners-9-to-18-inch.php</A></DIV>
<DIV><FONT size=4>Prices seem reasonable. Far less than GKR screws that I
love. However, the screws are a significant cost. My original intent
was to mount 12”eps over the roof sheathing. However, using a spacing of
2’oc on furring strips that are also at 2’oc, it results in 4 screws/4sf, or 1
screw/sf. On the walls, my 6”foam is setting on the foundation with no
significant loading except for wind suction. My site is windy. For
this I need am planning a 9.5” screw at </FONT></DIV>
<DIV><FONT size=4>$.50/screw in bulk. However, the thicker roof would need
16” screw for $1.22/screw. That is a significant sf upcharge. The
12”eps is only $1.56/sf. I am aspiring to keeping the cost down to create
more access for high performance. As a result of this cost, I made the
recommendation that we insulate the ceiling of continuous 4” eps mounted
below cheap plane jane truss to achieve the continuous thick air barrier with
cellulose toped off to achieve higher R value. I believe this is the most
cost affective way to top off the thermal envelope. However, my clients
want to develop the attic. Therefore, we are back to wrapping the insulation
above the roof sheathing. However, because of the cost of the fasteners, I
am looking to skin it with only 6” foam to achieve thick air barrier and put
some insulation in between attic truss top chord to increase the R value.
Fiberglass would be the easiest. Because of the above roof eps, it
probably would be ok, even though it is air pervious. I would follow <A
href="http://www.buildingscience.com">www.buildingscience.com</A> ‘s
recommendation for proportion of air pervious to non air pervious to insure
inner most foam temp remains above dew point in winter with 50% relative
humidity in house. </FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>However, I am wondering if you could precisely cut eps foam to
the exact 22.5” spacing between truss top chord mounted at 24”oc. I see
this as being installed during the framing with a friction fit. Since the
top 6” insulation achieves the air barrier requirement, I would not think
additional sealing would be needed. Even without sealing, the nature of
eps would be much tighter than fiberglass. It also turns out it is less
expensive. This could also be done at the band joist. Installing
during the framing allows the foam to be used as a spacer to create a tight fit
that would be difficult to achieve after framing. However, I have not seen
it done this way. Therefore, what are the risk that I am not seeing?
Or is this a reasonable idea to increase R value at a low cost?</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>List input is always appreciated. </FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>Eli</FONT></DIV>
<DIV><FONT size=4><A
href="http://www.conservationarchitect.net">www.conservationarchitect.net</A>
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