Thread: Double Vapor Barrier

I inspected a beach cabin on piers. The crawlspace is open to the elements (which is problematic) but I am more concerned about the black plastic stapled and taped to the floor joists. The local building inspector made them put down a vapor barrier on the ground but then allowed them to "weatherproof the fiberglass batts on the underfloor (*my interpetation). My inspector sense says its not right but can't think of the justification on why its wrong?

//Rick

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Hey Rick,

Someone recently posted a picture of a clear plastic installed to the underside of the joists (I think it was a week or 2 ago). It showed what will happen when you install plastic to the underside of the joists (mold, etc.).

I see that on almost every manufactured home.

Bruce,

That is more of a filter fabric material isn't it--- not a solid plastic? I've always thought that that stuff could breathe.

Originally Posted by Brandon Whitmore

Bruce,

That is more of a filter fabric material isn't it--- not a solid plastic? I've always thought that that stuff could breathe.

I've seen a lot of sheet plastic used as a vapor barrier on the bottom of the joists. It works great to keep the crawlspace dry in case of a plumbing leak.

Originally Posted by Bruce Breedlove

I see that on almost every manufactured home.

If that was not there, when the manufactured home arrived on-site, there would not be any insulation remaining under the floor.

I guess putting it under there to protect the crawlspace from leaks from above is okay - as long as it is on the monthly to-do list 'Punch holes in plastic sheeting under house to drain accumulated moisture out.'

OK even with the thread drift I think I can describe this one. The issue is the greenhouse effect that will occur with warm house on one side and cold air on the other. The condensation will soak the area and with the home as food create the moldy environment.

Manufactured homes have a dense mesh blanket that will breath. I will recommend that a product such as Tyvek replacement the plastic.

Thanks

//Rick

My vote would be for plywood with some vents through the plywood as a permanent solution.
Rodents/ pests are gonna love the easy access to the home through Tyvek/ plastic materials, not to mention what could happen with gusts of high wind.

Originally Posted by Rick Bunzel

Manufactured homes have a dense mesh blanket that will breath. I will recommend that a product such as Tyvek replacement the plastic.

Then I would make the recommendation 'to replace the plastic sheeting with a product which can breathe, as is used under the floors of manufactured homes'.

Specifically stating Tyvek could get you into some serious money and trouble if the Tyvek does not work out over the long run.

Tove would probably work great but being a cabin next to the lake and the animal thing plywood would be the best bet and seal it off altogether but access area to get at drains and such.

Ah, scratch that, water leakage from above would be a serious concern. Tyvek is the only way to go. Lets moisture out one way (down) and lets it breath as well and keeps the moisture from coming up from below and keeps the breeze off the insul. You say cabin then it must not be to big. A roll of tyvek does not cost much at all. Tyvek tape for the seems.

What I included in my recommendation is that they consider some type of barrier or skirting to prevent animal/ rodent intrusions.

What is the point of a vapor barrier on the ground if the crawl space is open on all sides?

"What is the point of a vapor barrier on the ground if the crawl space is open on all sides?"

Keeps the dogs from getting mud on them.