Crawl space: Vapor barrier on vapor barrier

[roufamatic]

A contractor recommended we upgrade our home's vapor barrier in the crawl space as it was thin and tearing in places. He laid a new, thicker barrier atop the old.Recently another contractor saw this and was displeased. She claimed that the two layers of plastic could cause moisture to be trapped between, leading to mold. She recommended a do-over, removing everything and laying a new barrier properly.Is there merit to her suggestion? It seems to me that as long as the barriers are abutting, and are both on the ground, that the real risk (moisture rising into the crawl itself) is minimal. But I have no idea.

[HayZee518]

vapor barrier

your contractor is correct. two layers opposed to one is counter productive. I would strip the existing down to the framing and put in new barrier. a thicker barrier won't solve anything. making sure the edges and joists are airtight is better. watch the tv - homes on homes. DIYTV he always installs a vapor barrier with that orange sticky tape at joins and wall corners.

[pushkins]

I think the poster is referring to vapor barriers on the crawl floor. None the less a dual layer is not advisable, while it will restrict any ground moisture in the crawlspace moisture will in fact build between the two layers of visqueen (plastic). Code doesn't allow dual layers, overlapping seams should be 6"-8". Having said that, with two layers there is little risk of this causing mold growing on the floor joists etc... as the moisture will be trapped between the two layers of plastic, it will remain as moisture not mold as between the plastic there is nothing for mold to feed on and grow, mold needs cellulose (wood , paper etc...) to feed on and grow. If it were me, I'd be removing the torn original plastic and reinstalling the new over the crawl floor area.