Underlayment Thickness Help

[cwbolyard]

Hello all! Remodeling a 1986 home, pulled the carpets up, and found press board underlayment. I am taking that up and replacing it with plywood and then LVP. The subfloor appears to be 1/2 inch plywood and the underlayment was 5/8th I believe. The subfloor feels weak to me and dips more than I expected when stepping between joists. Maybe this is normal? The floors are pretty smooth but I have read so much about having glass smooth floors for LVP and to avoid any future issues wondered how thick to replace the underlayment layer. THE QUESTIONS: Should I use 19/32 or 23/32 on top of the plywood subfloor, what length screws should I use, and should I screw the underlayment into the joists? The price difference getween 19vs23 isnt much. Is it worth it or am I a paranoid first time home flipper? Thanks

 

[Sparky617]

By "pressboard" do you mean particle board (basically glued sawdust) or Oriented Strand Board OSB (large pieces of wood glued together? Given the age it could be either. OSB has been around for at least 45 years now, but I think particle board has been around a lot longer. My first house built in 1984 had 7/16" OSB roof sheathing, I think the subfloor was plywood though. 1/2" will have considerable flex when put on 16" OC joists.

For your subfloor with LVP IMHO you'd be better off with Advantech tongue and groove OSB instead of plywood. Plywood can have voids in the interior layers. A skinny high heel can break through the LVP and top layer of plywood if there is a void. OSB doesn't have voids. I'd screw and glue the Advantech. I've heard people go screw it in-between the joists and others say into the joists. I would screw the existing down to the joists, especially if it was nailed and not screwed. This will keep the floor quieter. Don't use drywall screws for securing the subfloor. They can and will break.

 

[cwbolyard]

By "pressboard" do you mean particle board (basically glued sawdust) or Oriented Strand Board OSB (large pieces of wood glued together? Given the age it could be either. OSB has been around for at least 45 years now, but I think particle board has been around a lot longer. My first house built in 1984 had 7/16" OSB roof sheathing, I think the subfloor was plywood though. 1/2" will have considerable flex when put on 16" OC joists.

For your subfloor with LVP IMHO you'd be better off with Advantech tongue and groove OSB instead of plywood. Plywood can have voids in the interior layers. A skinny high heel can break through the LVP and top layer of plywood if there is a void. OSB doesn't have voids. I'd screw and glue the Advantech. I've heard people go screw it in-between the joists and others say into the joists. I would screw the existing down to the joists, especially if it was nailed and not screwed. This will keep the floor quieter. Don't use drywall screws for securing the subfloor. They can and will break.

Yes it is particle board. So you would go with an OSB tongue and groove over a plywood for LVP?

 

[Sparky617]

Yes it is particle board. So you would go with an OSB tongue and groove over a plywood for LVP?

I would, yes. Some people don't like OSB, but it is a great product for this application.