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To add vapor barrier or not?


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Those of the bretheran familiar with the great NW, is there a time when a vapor barrier is not required on the "dirt" crawl space floor? The reason I ask. Today I had a new construction home in which the builder put 4" pea gravel on the crawl space floor but there was no vapor barrier on top. My initial thought is that the vapor barrier should still be required, just wanted to be sure prior to calling it out.

And yes, that was one comfortable crawl...

Thanks.

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Hi Robert,

It's technically not required if the minimum net-free area of ventilation openings is not less than 1 square foot for every 300 square feet of under-floor area. One ventilation opening needs to be withing 3ft. of each corner of the building, except one side is permitted to have no openings.

ONE TEAM - ONE FIGHT!!!

Mike

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If there is proper ventilation then there is no need to install vapor barrier .

I disagree. There is code and then there is what you can see, smell and feel. I've seen hundreds, maybe thousands, of crawlspaces where the venting met code and there were moisture issues and I've seen just as many that met code and didn't have any issues.

The physical condition of a house doesn't care what's written in a code book. The house will do what it's going to do; it's our job to spot those issues, make the client aware of the implications and give them a sensible recommendation.

I'm in Robert's region. I know that a lot of builders around here will use pea gravel to raise the level of the crawlspace floor above water intrusion so that it appears like there is a very nice dry crawlpace. When I see a crawl full of pea gravel, I dig down as deep as I can to see how far below the surface I'll find the water and I'll always recommend a barrier - even if the ventilation is well above the code minimimum required to justify ditching the barrier.

Consider it a belt and suspenders approach. Most builders don't argue about it; a barrier is cheap and they, like us, know that they only see a crawl in a snapshot of time - there's no telling what might happen six months down the road - so why not put a barrier in to be on the safe side?

ONE TEAM - ONE FIGHT!!!

Mike

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My old crawlspace 1970 vintage, had pea gravel in the addition. In the winter, it becomes wet gravel. I added a poly vapor barrier and it was better.

This year, I spread the old pool liner, must be 20 mil or so, over the poly, white side up. Now, I can roll around in there all day and comes out clean and dry. [:)]

I have seen occasional old dirt crawls that were dusty dry. House on a dry slope or top of a hill.

New construction here is always concrete skim coat over poly in the crawl. It should be a universal rule.

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If there is proper ventilation then there is no need to install vapor barrier .

I disagree. There is code and then there is what you can see, smell and feel. I've seen hundreds, maybe thousands, of crawlspaces where the venting met code and there were moisture issues and I've seen just as many that met code and didn't have any issues.

The physical condition of a house doesn't care what's written in a code book. The house will do what it's going to do; it's our job to spot those issues, make the client aware of the implications and give them a sensible recommendation.

I'm in Robert's region. I know that a lot of builders around here will use pea gravel to raise the level of the crawlspace floor above water intrusion so that it appears like there is a very nice dry crawlpace. When I see a crawl full of pea gravel, I dig down as deep as I can to see how far below the surface I'll find the water and I'll always recommend a barrier - even if the ventilation is well above the code minimimum required to justify ditching the barrier.

Consider it a belt and suspenders approach. Most builders don't argue about it; a barrier is cheap and they, like us, know that they only see a crawl in a snapshot of time - there's no telling what might happen six months down the road - so why not put a barrier in to be on the safe side?

ONE TEAM - ONE FIGHT!!!

Mike

I'm not sure that's correct. Don't have time to look it up right now but gotta get ready for the kids' b-day party. . .

I believe the only time a VB is not required is when there's concrete on the ground.

Could be wrong. . . .

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