[Greenbuilding] Most permeable air barrier

[John Salmen]

I would think the major design goal for a sugar shack would be ventilation – and aren’t the evaporators hooded these days – stainless steel vent hood kind of thing either mechanical or with a large chimney – old ones I was in as a child had big open cupolas 

 

From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of jfstraube at gmail.com
Sent: August-31-15 9:19 AM
To: Matt Dirksen; Green Building
Subject: Re: [Greenbuilding] Most permeable air barrier

 

Now you are second guessing design goals. 

 

Sent from my BlackBerry 10 smartphone on the Bell network.


From: Matt Dirksen

Sent: Monday, August 31, 2015 10:19

To: Green Building

Reply To: Green Building

Subject: Re: [Greenbuilding] Most permeable air barrier

 

" 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."

 

EVent is considerably more vapor permeable than any of the Gore products.

 

Regardless, opening up some pit zips will beat the hell out of any vapor permeable material, when it comes to attempting to reduce moisture build up.

 

On that note, I'd assume a good, properly sized, ventilation system would be far more effective (and cost effective) toward removing moisture, then speccing some $$ permeable membrane.

 

Especially in a specialized application like a maple sugar shack.


Matt


On Aug 31, 2015, at 9:52 AM, RT <ArchiLogic at yahoo.ca> wrote:

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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