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.