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Vapor barrier - crawlspace


Bonne
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My question: Is it typically recommended to install the 6 mil vapor barrier to lie FLAT up to the piers on the ground of the crawlpace? Not tented over the pier pads? This is what I recommend and the contractor / installer wants to argue. I need something to support my opinion - or not. Thanks

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Either way will work as long as you are ensuring as close to 100% coverage as you can get.

The trouble with lying the barrier flat is that, unless you stake it in place with sod stakes or something similar, just about anyone that crawls around under there is going to dislodge it and then you've got big swaths of uncovered soil evaporating moisture into the crawl. On the other hand, if the barrier is tented over the piers and there is a tear in the barrier, it's evaporating the equivalent of the square footage of all soil not actually in contact with the barrier into the crawl.

I usually instruct to ensure the barrier overlaps the footers, overlaps at least a foot at adjacent sheets, is carefully trimmed so that it fits tightly around the base of piers and is staked in place so it can't be dislodged. I then point out that in the ideal installation the barrier is adhered and sealed to the sidewalls above the footers, at all overlaps and to the top of piers with latex mastic but not staked. That way, if you get a little groundwater infiltration but not enough to reach the top of the footers or the piers, the barrier can float up with the water and recede with the water as it subsides and you don't get any moisture at all evaporating under the home.

If it looks like it's going to be an installation where it's likely to flood heavily (I can think of one on the flood plain of the Snoqualmish like that) there needs to be a drain installed through the barrier if it's installed tightly like that, so that once the water recedes you aren't left with large ponds of water trapped on top of the barrier in the low spots. In a situation like that the barrier is pretty useless during flood stage anyway.

There's one company locally (Willard's Pest Control) that installs barriers that way and it works great.

ONE TEAM - ONE FIGHT!!!

Mike

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Either way will work as long as you are ensuring as close to 100% coverage as you can get.

The trouble with lying the barrier flat is that, unless you stake it in place with sod stakes or something similar, just about anyone that crawls around under there is going to dislodge it and then you've got big swaths of uncovered soil evaporating moisture into the crawl. On the other hand, if the barrier is tented over the piers and there is a tear in the barrier, it's evaporating the equivalent of the square footage of all soil not actually in contact with the barrier into the crawl.

I usually instruct to ensure the barrier overlaps the footers, overlaps at least a foot at adjacent sheets, is carefully trimmed so that it fits tightly around the base of piers and is staked in place so it can't be dislodged. I then point out that in the ideal installation the barrier is adhered and sealed to the sidewalls above the footers, at all overlaps and to the top of piers with latex mastic but not staked. That way, if you get a little groundwater infiltration but not enough to reach the top of the footers or the piers, the barrier can float up with the water and recede with the water as it subsides and you don't get any moisture at all evaporating under the home.

If it looks like it's going to be an installation where it's likely to flood heavily (I can think of one on the flood plain of the Snoqualmish like that) there needs to be a drain installed through the barrier if it's installed tightly like that, so that once the water recedes you aren't left with large ponds of water trapped on top of the barrier in the low spots. In a situation like that the barrier is pretty useless during flood stage anyway.

There's one company locally (Willard's Pest Control) that installs barriers that way and it works great.

ONE TEAM - ONE FIGHT!!!

Mike

Thanks for your reply!

I frequently find the vapor tented with the cardboard or form wood left on piers. With the vapor tented the cellulose debris quickly takes on moisture and deteriorates. Often there is mold / mildew. I am convinced that the vapor should be installed flat up to the piers with good overlap at seams and it would be nice if it didn't get disturbed. I have only seen vapor taped in one or two crawlspaces in 8 years!

Best,

Bonne

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My question: Is it typically recommended to install the 6 mil vapor barrier to lie FLAT up to the piers on the ground of the crawlpace? Not tented over the pier pads? This is what I recommend and the contractor / installer wants to argue. I need something to support my opinion - or not. Thanks

It's not worth arguing. Either way works just fine. Frankly, my personal favorite method is to make the floor of the crawlspace as flat as a pancake, install the vapor barrier over it as tight as a drum, and then place the piers on top of it.

- Jim Katen, Oregon

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