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Is the vapor barrier located on the ground or on the bottom of the joists? What do you mean by exposed ends? Do you mean the edges between the fiberglass insulation?
The proper way to construct a floor system over a crawl space is to install a kraft-paper faced fiberglass batt insulation into the joist bays with the kraft paper facing tight against the floor sheathing. Code requires that the vapor barrier is on the warm side in winter. Once the insulation is fully installed then you should install an air barrier over the bottom of the joists. Tyvek is a good material for this, but anything that is an air barrier will work. DO NOT put a vapor barrier at the bottom of the joists as it will trap moisture in the floor deck and create mold. The air barrier is to stop the movement of air through the fiberglass insulation. Allowing air to circulate through the fiberglass reduces its effect R-value significantly. Think of adding the tyvek to your attic space to if you have exposed fiberglass. The 6-mill poly vapor barrier should be laid against grade and if possible protected by some kind of overlay if you access the space regularly. Having only two vents within the space should be adequate if they are free or dirt and debris and are located on opposite sides of the space to assist in a true cross-ventilation.
The proper way to construct a floor system over a crawl space is to install a kraft-paper faced fiberglass batt insulation into the joist bays with the kraft paper facing tight against the floor sheathing. Code requires that the vapor barrier is on the warm side in winter. Once the insulation is fully installed then you should install an air barrier over the bottom of the joists. Tyvek is a good material for this, but anything that is an air barrier will work. DO NOT put a vapor barrier at the bottom of the joists as it will trap moisture in the floor deck and create mold. The air barrier is to stop the movement of air through the fiberglass insulation. Allowing air to circulate through the fiberglass reduces its effect R-value significantly. Think of adding the tyvek to your attic space to if you have exposed fiberglass. The 6-mill poly vapor barrier should be laid against grade and if possible protected by some kind of overlay if you access the space regularly. Having only two vents within the space should be adequate if they are free or dirt and debris and are located on opposite sides of the space to assist in a true cross-ventilation.