2nd layer of plywood or use existing floor for spacing.

Hi

I am installing a new wide plank pine floor in my home. The room currently has 3 layers; Carpet, 3/4" Pine planks and 3/4" plywood. I removed the carpet and now deciding if I should remove the existing pine planks. They are currently face nailed and come up easy. In order to keep the transition height between rooms level I could either install over the existing 3/4" pine or remove the old planks and replace with a second layer of plywood. Which is preferred? If I put down new plywood should it be T&G and should it be glued and screwed?

Thanks Bob

 

In your case, you can put down 5/8"- 3/4" if plywood or 3/4" Advantech (if OSB) which is a T&G product. Optimally, you want a T&G floor for added strength. Do not glue the 2nd layer to the first. Remove the existing poorly adhered planks, screw down the original subfloor to eliminate squeaks, install your second layer to the first with the strength axis across the joists, but screw down to the ply and miss the joists. Use exterior deck screws as other screws are not rated for flooring applications.

 

Ok that all sounds good. Question, why is the standard recommendation to miss the joists when installing a second layer of plywood? I have read it is to decouple the finished floor from the joists and protect from movement? If true, then what would you do in the case your finished floor sits directly on one layer of plywood? -Bob

 

Bob, you wouldn't have a decoupling problem if you only had one layer of plywood. It is basically meant to allow the two layers of plywood to be decoupled from each other and the joists below. The movement is so minimal, but it is there. Good luck with the project, and let us know if we can help further.

 

>you wouldn't have a decoupling problem if you only had one layer of plywood.<
sorry for not understanding. If I only had one layer of plywood my finished floor would move with the joists, since the single layer would be attached with the joists. Now if we add a 2nd layer of plywood, I don't see why you can't screw the 2nd layer of plywood through the first and into the joists? Thanks Bob

 

I think it helps control squeaking and/or buckling .... I don't know for sure

For what it is worth, when I installed plywood over my subfloor I screwed them to the joists thru the subfloor and used drywall screws because I didn't know better. Not sure if I was just lucky or what but that was about 18 yrs ago and my floors are still level and squeak free.

 

If you screw the second layer to the same joists as the first layer, they the two sheets which will expand and contract at different rates will fight the joists for dominance. Buy screwing to the first layer you effectively lock the floor as one unit and they will move together as one. Therefore less stresses on the floor system. This is exceptionally important when dealing with tile that would be subject to the movement by showing cracks in the finished floor system. With wood floors, it can result in movement of the fastening systems and result in a squeaky floor.

 

Now I understand, thanks!