Good morning! I'm in the process of installing hardwood strip flooring in my home. I was previously carpeted. I've pulled up the carpet and found 5/8" particleboard underlayment over 5/8" plywood sheathing. I removed the particleboard and screwed down the sheathing to eliminate squeaks. I put down AquaBar over the sheathing as a moisture barrier. I then screwed down a layer of 5/8" plywood sturdifloor.

My question is whether this will be adequate as a moisture barrier? My plan is to put down rosin paper over the sheathing with the flooring going down directly over the rosin paper. Originally I figured the rosin paper would help as a secondary moisture barrier as well as help deaden sound. On hardwoodinstaller.com rosin paper is not recommended as a moisture barrier.

I've racked out flooring to install this weekend but don't want to screw up now. By the way all flooring is either over joist (second floor) and solid T&G decking on the first.

Any help would be appreciated.

You can use the same Aquabar "B" laminated paper over your newly installed plywood underlayment. It is made for wood floor installations, among other things.

Thanks for the reply. Are you saying I shouldn't use the rosin paper and need another layer of moisture barrier?

Well, regardless of what Fortifiber says, Aquabar "B" is not a moisture barrier. Once someone finishes driving all the nails through the flooring and the paper, it's not nearly as moisture resistant. We consider it a moisture VAPOR REDUCER/DIFFUSER. It is superior to rosin paper in vapor reduction. It will not stop a floor from cupping if there is a lot moisture below the floor; nothing will except removing the source of the moisture. If you only want to "cushion" the floor and assist in helping prevent squeaks, the rosin paper is fine for that. 15 lb. asphalt saturated felt is typically the recommended product to go under 3/4" flooring. This should have been spelled out in your installation instructions. So, for 3/4" flooring, 15 lb. asphalt saturated felt is what both NOFMA, the NWFA and most flooring manufacturers specify to go under the flooring. For thinner nailed down floors, like 3/8" and 1/2" engineered, I prefer the thinner Aquabar B. If you are on the second floor with climate controlled living space below, then the red rosin will work fine, as it mostly just cushions the flooring to assist in preventing squeaks and keeps the dust down during installation. Plus, it makes the flooring slide easier to also assist in the installation. But it isn't a moisture barrier. Neither is the Aquabar or 15 lb asphalt felt.