Plywood over plank subfloor questions

Old 03-02-22, 10:34 AM
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Plywood over plank subfloor questions

Hello, New poster and new homeowner here.

I have a few questions regarding putting plywood over my current plank subfloor. Iíll start buy saying I have already secured my planks to the joists and eliminated all squeaks.

I plan on putting plywood on top of my plank subfloor before finally adding vinyl plank as a finish.

1) What thickness plywood is recommended? Pros and cons to different sizes?

2) Should I screw the plywood directly to the planks or to the joists?

3)Is a membrane/paper required between the two layers of subfloor ?

Im open to any tips, pointers, tricks as this is a first for me

Thanks in advance
Old 03-02-22, 10:54 AM
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1. That totally depends on what you need. If the subfloor is stiff and flat then something as thin as luan can be used to simply provide a smoother surface. As the need for structure goes up so does the thickness of the sheeting. You eventually reach a point with 3/4" plywood or OSB where the sheeting alone can span 16" between joists pretty well and if you use 3/4" Advantech it can span that distance and be rock solid even without a subfloor.

2. I've heard it recommended both ways. After a couple decades maintaining older rental houses I screw through the sheeting and into the studs. Many older subfloors just don't stay attached to the joists very well. Nails work loose and boards split. Screwing, not nailing, into the studs securely sandwiches the subfloor so even a split board can still provide some strength to the floor.

3. I generally do not install a membrane or anything between layers though I think it is a good idea in some cases. If the subfloor is pretty decent you can glue or just screw the sheeting down and not have too many squeaks. If the subfloor is in more poor condition, even after you've nailed it back down, the planks can come loose and move causing squeaking. Of course this does nothing for the subfloor squeaking against the joists but you potentially can prevent some squeaks. A membrane between layers can be helpful if water leaks are a possibility. A membrane between layers can stop the water from damaging rooms below. It can also trap the water so any leak can spread further and not dry out as quickly so it's a judgement call. Again, I usually don't do it.
Mark Curry voted this post useful.

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