<!DOCTYPE html><html><head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<!--[if !mso]><style>v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style><![endif]--><style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:HelveticaNeue-Light;}
@font-face
{font-family:HelveticaNeue-Medium;}
@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;
mso-fareast-language:EN-US;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
p.MsoPlainText, li.MsoPlainText, div.MsoPlainText
{mso-style-priority:99;
mso-style-link:"Plain Text Char";
margin:0cm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;
mso-fareast-language:EN-US;}
span.PlainTextChar
{mso-style-name:"Plain Text Char";
mso-style-priority:99;
mso-style-link:"Plain Text";
font-family:"Calibri",sans-serif;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;
mso-fareast-language:EN-US;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 72.0pt 72.0pt 72.0pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
<style type="text/css">body { font-family:'Times New Roman'; font-size:17px}</style>
</head>
<body lang="EN-CA" link="#0563C1" vlink="#954F72">On Sun, 30 Aug 2015 14:10:44 -0400, Ross Elliott <relliott@homesol.ca> wrote:<br><br><blockquote style="margin: 0 0 0.80ex; border-left: #0000FF 2px solid; padding-left: 1ex">
<div class="WordSection1">
<p class="MsoPlainText"><span lang="EN-US" style="mso-fareast-language:EN-CA">I know Tyvek is way more permeable to water vapour than Typar, which are the only two choices available locally, but I'm building a sugar shack, which as its primary function is to
dissipate a tremendous amount of water vapour. I don't want the water to condense on the ceiling air barrier, otherwise it may drip back into the syrup. What's the absolute most vapour-permeable air barrier on the market, including those esoteric European
membranes?</span></p>
<p class="MsoPlainText"><o:p> </o:p></p></div></blockquote><div><br></div><div>I have no idea nor have I looked at any product tech data numbers but I doubt that any building sheet membrane air barrier product is more vapour-permeable than the "breathable" Gore-tex liner that is inside some of the jackets that I wear in winter.</div><div><br></div><div>On those garments I find that after strenuous activity (when it's really cold out) the inside of the jacket will often be dripping wet with condensed perspiration.</div><div><br></div><div>I suspect that what's happening is that the heat loss from my body is not enough to keep the transpired perspiration in vapour phase so that it can be moved through the vapour-permeable Gore-tex membrane which of course does not permit liquid-phase moisture to pass through. </div><div><br></div><div>I don't know how voluminous your sugar shack will be so I have no idea what the interior temps will be at the building envelope and whether the temps at the interior surfaces will be sufficient to drive the moisture past the air barrier but I suspect that a more prudent strategy would be to assume that there will be condensation and </div><div><br></div><div> (a) provide details to collect and route that condensation to where it can't cause trouble <br></div><div><br></div><div> and/or</div><div><br></div><div> (b) use hydrophilic materials inside of the air barrier that will be able to suck up the moisture (ie like a sauna) </div><div> </div><div> or</div><div><br></div><div> (c) design the sap boiling apparatus as a closed system ( you know, like your mescal juice still) so that the evaporate can be collected and directed to where it can't cause trouble.</div><div><br></div><div> </div><div><br></div><div><br></div><br><div id="M2Signature"><div>-- </div><div>=== * ===<br>Rob Tom DT7-64 <br>Kanata, Ontario, Canada</div></div></body></html>