Vapor barrier under basement floor
I have a ten year old house that has a 6mil vapor barrier under the slab. There is about six inches of crushed gravel under that and native sand even lower. The basement is a walk-out and we’ve never really had any water issues. We do run a dehumidifier in the summer months.
We are finishing the basement and adding Coretec Pro Plus Vinyl Plank flooring. The instructions are vague about adding a vapor barrier between the slab and the vinyl flooring.
I was wondering what everybody’s opinion would be about this. I can see two arguments:
1. Adding another layer of plastic on top of the slab would help preserve the vinyl flooring and isolate any water vapor.
2. But I could also see this trapping any normal moisture/vapor between the slab and the plastic, creating it’s own set of problems.
So what do people think? Should I add another vapor barrier or not?
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Neither vinyl nor concrete are damaged by moisture.
A redundant vapor barrier on top of the slab doesn't hurt anything, but it doesn't buy you anything either.
Thanks for your reply. It just seems like I am sandwiching the concrete in plastic. I can see that as a bad thing. I worry that it would just trap water/vapor under the slap and start growing mold on any little bits of dust or dirt that might get trapped under there.
I agree with Dana. Either way is fine. If you have poly under the slab, you don't need another layer of poly -- but if you install it, no harm is done.
Don't worry about what happens under the poly. It doesn't matter.
I'm going to be that guy: vinyl, except in critical applications where there is no suitable alternative, can never be considered a "green building" material. I believe this should be mentioned here at Green Building Advisor.
Unless you believe in perfect air sealing, stick to the recommendations below.
That's a really interesting read. Thanks!