[Greenbuilding] Most permeable air barrier

[RT]

On Sun, 30 Aug 2015 14:10:44 -0400, Ross Elliott <relliott at homesol.ca>  
wrote:

>
> 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?
>
>

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.

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.

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.

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

     (a) provide details to collect and route that condensation to where it  
can't cause trouble

                                and/or

    (b) use hydrophilic materials inside of the air barrier that will be  
able to suck up the moisture (ie like a sauna)

                                       or

    (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.





-- 
=== * ===
Rob Tom DT7-64
Kanata, Ontario, Canada
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