Condensation on duct in crawlspace

This house is in the deep south. The ducts in the crawlspace were recently wrapped with the insulation shown to help with a condensation problem. I don’t know how bad it was before but you could wipe water off this insulation and there were puddles below. The insulation had a label saying it provided an R 8 with an air space and an R 4 without. The insulation was double wrapped so it should have the minimum recommended which is an R 8. I’m thinking a thick well wrapped fiberglass bat would provide a higher R factor and take care of the problem. Has anyone else seen problems with this insulation in the crawlspace?




Let me guess, the crawl was ventilated and it was hot & humid outside, correct? Those vents allow humdity in the cooler crawlspace (and cooler surfaces e.g. ductwork, plumbing pipes, etc.) and voila!, condensation. Looks like the joist bottoms have some staining/growth as well from high humidity in the crawl, which is your culprit.

Solution? Encapsulation.

Either encapsulation like Josh said, or swap the ducts out to plastic flex. I never recommend aluminum ducts in the crawlspace down here.

Insulation does not prevent condensation, just as it does not prevent freezing outdoor pipes in the winter (It just slows things down).

If you do not collect psychrometric readings of the air no one here can give you any reasonable advise.