Insulating Crawlspace, vapor barrier controversy

I'm currently in the process of insulating the floor over my crawlspace to increase the comfort level in the house during winter. This is our second winter in the house and from experience, the floors were cold, extremely cold. We live in Eastern Canada, so minus 35 Celsius is not out of the ordinary.
So far, I have been in the crawlspace and have laid down a vapor barrier over the dirt floor (full coverage, taped seams etc.) but I am concerned about the fragile fiberglass insulation that I will be installing between the floor joists. From experience, I know that a vapor barrier always faces the warm side of the building to prevent moisture from migrating into the insulation and condensing. This makes sense as there is more moisture inside in winter than out, however, I have a gut feeling that a crawlspace will always contain more moisture regardless of steps taken to alleviate it. So, I am contemplating placing a second vapor barrier under the insulation (attached to the joists) to protect it from the moisture in the crawl.
My questions is, how do I protect the insulation? How much moisture would realistically flow from inside the house into the crawlspace through the floors trapping condensation in the fibreglass? I can't imagine the flow would be anywhere near that of walls and ceilings. Also, my subfloor has two layers of 6 mil poly underneath it, plus my flooring is 3/4" tongue and groove pine with three coats of Varathane.
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Rob Landry wrote:

Those two layers of poly will make a good vapor barrier. You need not worry about the moisture getting into the fiberglass.
Consider this. The moisture will be something at or below 100% in the ventilated space. All else being equal as air warms it can absorb more moisture so the humidity goes down. So as the air might move through the fiberglass it will also be warmed and as it warms it will have a lower humidity, so it will always be less than 100%.
The problem comes from the other way. The warm air in the house may be 60% humidity but as it travels out through the insulation and cools to say -10C it may now be super saturated and condensing on whatever is cold like your wood and fiberglass. It's like the moisture that forms on you glass of iced tea and what you are going to have is a cup of hot tea, so don't worry.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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"Rob Landry" >

Check http://www.buildingscience.com/ for a wealth of climate specific best practices information.
Will
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Great site, wealth of info.
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