I recently assisted a group doing Hurricane Sandy relief work. Many of the affected houses had crawlspaces which had been flooded. The group’s approach to re-insulating was to install fiberglass batts, paper side up, between the floor joists, then staple Tyvek to the bottoms of the joists. I’m not sure what the thinking behind this is. My concern would be the trapping of water caused by condensation in the joisy bays. Any thoughts?
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Replies
The paper side should, indeed, be uppermost, facing the warm side, to help retard moisture migration from the living space into the insulation batts.
As for the Tyvek, although I don't see the need for it, there is no harm in having it there. Tyvek is not a vapor barrier--it's an air barrier, but there is very little point to it in a crawlspace "ceiling."
So, to address your concern about trapped moisture, the paper facing on the batts will help prevent it, and the Tyvek won't create a trap for it in the batts since it does not prevent passage of water vapor.
Although it's certainly true that convection currents passing thru batt insulation will reduce its insulatiing performance, is it really true that the crawlspace insulation will lose "most" of its inslulating value by not having an air barrier on the underside?
To me, of all the applications where batt insulation could be subjected to convection currents, this one ought to be the one most nearly inert. (Say, compared to attic blown-in insulation or attic knee walls lacking 6-sided air barrier coverage.)
air wash...
Air wash can reduce the effective R-value of FG insulation. Ironically, this is what Tyvek was originally designed for...to go over FG batts in attic joist bays to minimize air wash loss. But no one used it since it was an "invisible upgrade" and no one knew or cared about air wash losses.
So they then remarketed it as a house wrap. A house covered in Tyvek became visible, and a great source of advertising on it's own. Everyone wanted it. Unless they were smart enough to know better. lol
Covering crawlspace insulation with Tyvek will reduce/eliminate rodent infestaion into the insulation.
What? You got rodents with out claws or teeth?
Its not unheard of, they make small utility knives.