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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">The cob is about 20mm thick so that it covers and seals the
buck. The foam is about 20 – 30 mm and extends the depth of the window,
which is generally about 140mm. I agree that the cob would generate a small
thermal bridge where it is used to cover the buck. Our buildings are all over
Australia, but mainly focused in the southern states including Tasmania. We are
located in central Victoria where frosts drop the temperature to -4 C on
a regular basis in our winter, and on occasions as low as -10 c. </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Brian</span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">
<a href="mailto:GSBN-bounces@sustainablesources.com">GSBN-bounces@sustainablesources.com</a> [mailto:<a href="mailto:GSBN-bounces@sustainablesources.com">GSBN-bounces@sustainablesources.com</a>]
<b>On Behalf Of </b>Derek Roff<br>
<b>Sent:</b> Thursday, 22 November 2012 8:37 PM<br>
<b>To:</b> Global Straw Building Network<br>
<b>Subject:</b> Re: [GSBN] Window Detailing Question</span></p>
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<p class="MsoNormal">If I understand correctly, the cob forms a thermal bridge
between the inside of the house and the outside, in the space around the edges
of the windows. What percentage of the 100mm width is cob, and what
percentage foam? What climate are you building in?</p>
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<p class="MsoNormal">Derek</p>
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<p class="MsoNormal">On Nov 21, 2012, at 11:58 PM, Brian Hodge wrote:</p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Hi all,</span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Some time back we began enveloping the window buck in render/cob
so that the buck is completely covered and sealed. The window is then
fixed in position with the use of expanding foam. The expanding foam is a
mechanical connection which also provides insulation and a water proof seal. By
doing this there is no entry point for water , which normally happens around
the junction of the timber to render. We complete the second coat of render
before fitting the windows, which also assists in the drying of the second coat
inside due to the increased air flow by not having the windows in place.</span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">The expanding foam needs a dust free surface to adhere to, so we
treat the surface of the render in alignment with the window with 10 parts
water to 1 part bondcrete, which stabilizes the render. We have now been using
this method of window installation for about 6 years and even in high wind
applications we have never had cracking around windows or any water leaks.
Obviously in order to do this you must allow a significant amount of clearance
between the buck and the window to allow for the cob & render. We allow
100mm in the width and 60 in the height.</span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">The foam must be overfilled so that the excess foam can be cut
of broken off as this gives a surface that the render will adhere to, where-as
the natural finish is too smooth. Once the window is held in place with the
expanding foam, we use cob around the window to generate the final shape
required, which also provides a very strong structure around the window.</span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">This method of construction is obviously of no value to people
unwilling to use expanding foam, but it has served us well, and completely
solved the problem of leaks around the windows.</span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">I trust this helps someone.</span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Regards</span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Brian</span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black"><br>
Derek Roff</span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black"><a href="mailto:derek@unm.edu">derek@unm.edu</a></span></p>
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