Vapor/Moisture Barrier needed?


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Old 01-15-09, 04:41 PM
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Question Vapor/Moisture Barrier needed?

I will be installing carpet in my bottom floor soon. I have a wood subfloor that sits on a concrete slab. Do I need to put down felt paper as a barrier anywhere in my installation? Previously there was a layer of felt paper between the planks of the subfloor and the particle board underlayment. (There also appears to be felt paper between the slab and the subfloor joists.)
 
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Old 01-15-09, 05:48 PM
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What type of flooring was installed prior? Is this above or below grade? Basement? Slab above grade?

You had a particleboard underlayment. That's o.k. for carpet. Why did you remove it? Moisture issues?

More details are needed.
 
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Old 01-15-09, 06:02 PM
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You never would won't a VB under a floor! It will just hold moisture.
 
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Old 01-15-09, 06:26 PM
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You want a vapor retarder under laminate and hardwood as recommended by manufacturers. The questions here are why there is plywood over the concrete and if it is below or above grade. Sounds like a screed floor system with joists possibly 2x4's over concrete. No knowledge of system being above or below grade. No knowledge of moisture issues.

Whether installing laminate or wood over concrete, or gypcrete above grade on the 15th floor, a vapor retarder is required. Solid 3/4" hardwood is not recommended below grade, but it can be installed above screed system with vapor retarder beneath and another vapor retarder on top and beneath flooring above grade. Or, it can be installed with 3/4 plywood or OSB over vapor retarder on concrete above grade with another vapor retarder on top before installation.

The purpose of a vapor retarders is to keep the penetrating moisture from emitting to the flooring, whether over crawl space or basement or above grade concrete slab. Moisture issues cause cupping and crowning, which tend to be major issues with wood floors. All concrete has vapor emissions, even if vapor retarder was installed beneath.

Note 'vapor retarder' is not a 'vapor barrier.'

While engineered wood flooring is more dimensionally stable than 3/4" solid, it can be installed below grade on concrete WITH vapor retarder, as can laminate. It is extremely important to follow manufacturer's instructions re: subfloor prep, moisture tests, vapor retarders, and required underlayments. Each manufacturer tends to have its own very specific instructions which must be followed in order not to void warranty.

Vapor retarders are, indeed an important part of flooring installation. The purpose of vapor retarders is to retard moisture.

Let's back up to our camping days. You spread out a ground cloth before you pitch the tent. Why? To retard moisture. Modern day tents installed polypropylene bottoms which provide an additional vapor retarder. So with ground cloth underneath and the additional polypropylene tent bottom as an additional vapor retarder, we advanced long beyond the old days of the Army surplus pup tents, which were a piece of canvas, a couple of tent poles, and some pegs, and soaking sleeping bags and blankets in the back yard. Even with those two vapor retarders, sleeping bag still feels damp. You carry a clothes line and tie between two trees and air and dry out bedding before making it up again for the next night. Note: vapor retarders--not vapor barriers.

Yes, indeed, vapor retarders below flooring are important!
 
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Old 01-15-09, 09:04 PM
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twelvepole: Thanks for your response. We took up the floor because our first floor flooded. (We moved in in April '08) Our concrete slab is the foundation which is at grade (or maybe a couple inches below?) There is a layer of felt paper covering the slab. We have a wood subfloor w/ 2x4 joist and 1x6 plank. Above this WAS felt paper then particle board underlayment, followed by the finished flooring. We had mostly carpet, some hardwood, and linoleum.

Our plan is to put in more hardwood and some carpet. We were not having any moisture issues prior to the flood. I could just repeat the order of underlayment and felt paper that was already in there, but it doesn't jive with what I've been reading. For instance, shouldn't the barrier/retardant come between the underlayment and the finished floor for hardwood? (It was between the subfloor and the underlayment.

Then, for carpet in this situation, would it work to put the barrier/retardant between the subfloor and underlayment as the previous owner or perhaps the original builders had done.

Thanks again for your help. Luckily, I have a few weeks of letting stuff dry out before I start building again. So, plenty of time to get all my ducks in a row.
 
 

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