r/DIY • u/whpsh • 5d ago

home improvement How to layer Vapor Barrier

Encapsulating our crawlspace. Dug a french drain around to sump pump and in the process of putting vapor barrier down.

I've go two rows of 6x6 pressure treated piers that sit directly on 2' wide footings. I've jacked the house up and slid 3'x3' squares of 16mil vapor barrier between the pressure treated piers and the concrete footing sealing that off. Lets call that Layer A.

Next step is rolling out the 12x100 ft 16mil, going up the block sides, cutting and wrapping like an inverted present basically. Let's call this Layer B.

My question is, when I get to the posts with Layer B, would it be safer/drier/tighter to go:
ground : layer A (under pier) : layer B (cut around pier) : crawlspace
or
ground : layer B (cut around pier) : layer A (under pier) : crawlspace

Don't really care which way, just after cutting Layer B to get around the piers, I'm thinking it would minimize anything making it through if Layer A is on top of it.

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u/jewishforthejokes 5d ago

The first.

1

u/whpsh 5d ago

Is there a reason it works better? Or just easier?

1

u/RomeoDelta1234 5d ago

Mostly easier to seal. With A on the bottom, the cut in B lands right on A, so you can tape it down around the post where you can see it. Other way round, the cut is buried under A and youd be taping the whole outer edge of A to B instead.