Where should the vapor/moisture barrier go?

September 1, 2021 11:26 PM

I've taken up old carpeting and pad, and am installing a Pergo Vintage Linen Hickory floating laminate floor. Each board has foam underlayment attached. I've done a moisture test on the subfloor and see levels range from about 6% in most of the room to about 11.5% near three, floor to ceiling windows. Pergo says levels should be 12% or below.

Although the living room is above grade by about a foot, during the rainy times of the year, water tends to pool just outside of the house. The water table seems high there I think because of a small slope with ground cover about six feet away from the house. It's been very dry this summer, so I'm thinking when the rains come, the subfloor will soak some of it up and these numbers might not mean much.

The subfloor is already in place, so I can't put a moisture barrier below it. Can I put 6mil or higher plastic sheeting on the subfloor and then install the floating floor on top of it?

posted by CollectiveMind to Home & Garden (2 answers total)

Response by poster: Also, I've seen mentions about how the floor needs to breathe. If I put plastic over the subfloor, does that make it less breathable? Do I have alternatives if I can't get this to work?
posted by CollectiveMind at 11:36 PM on September 1, 2021

Adding an impermeable barrier can trap water in all kinds of bad ways, leading to rot. Unless the subfloor is concrete, I would not add an impermeable layer on top of it.

With water, the best solution is always start on the outside. Could you regrade or add drainage such that water does not pool close to the house?
posted by rockindata at 5:36 AM on September 2, 2021 [5 favorites]