Hi,

As was mentioned in this (link) thread, I am planning to install 3/8" plywood over my 5/8" OSB subfloor prior to nailing 3/4" solid maple. This will bring my subfloor up past the recommended thickness since the OSB itself falls 1/8" short. My question is whether or not it is sufficient to screw down the plywood (I'll be putting down a LOT of screws for no squeaking), or if it would be even better to also glue the ply as well as screw?

On the other hand, this may be unnecessary since the nails through the hardwood will essentially bind the two layers of subfloor anyway?

Please advise; thanks.

glue and screw(possibly staple?). Always better safe than sorry. I would refasten (with screws) the existing subfloor.

Thanks for the reply.
Would it be better to put down all of the screws once the 3/8" ply has been laid down? If I add screws to the existing subfloor and then add the plywood I will have a much higher chance of hitting the screws I just put in, wouldn't I? By adding all the screws through the extra layer of ply directly, I only have to contend with the more limited number of screws put in by the builder.

Does this make any sense or is it in fact preferable to add screws to the existing subfloor first and then again through the new layer? It is a new home if it makes any difference.

What type of glue is recommended for binding the plywood to the OSB?

Thanks again.

Screw the subfloor to the joist with screws. Then screw the additional plywood underlayment to the subfloor, with screws. Don't worry about hitting another screw. Back it out and move over.

Yellow wood glue is what I use.

Thanks again for the replies.
To clarify (sorry!), when I am doing the second step of screwing the additional plywood into the subfloor, should I be adding screws all over the place (i.e. where there are no joists) or only into the joists like I did in step 1 before adding the additional ply?

Many thanks

Ugh. I had thought I had 3/4" subfloor, but I was finally able to measure tonight after removing a floor receptacle, and I only have 5/8" also. I too am going to be installing 3/4" solid hardwood. I take it then, then I am going to have to add an addition layer of plywood over this?

This will have to go perpendicular to the first layer correct? 3/8" is how thick I want to go?

Sorry to hijack...it's more of a piggyback.

You re-nail/screw the subfloor to the joist before installing an underlayment. The 3/8 plywood UL is installed by spacing the fasteners every 6"-8" on center on the perimeter and about 8"-10" in the field. Don't worry about hitting the joist here. Leave an 1/8" gap between each sheet.



You will need a minimum layer of 3/8" if your subfloor is 5/8" OSB. The strongest way to run an underlayment is crossing the joist, same as the subfloor. But since you are using a 3/4" solid product either way you want to run it is OK. Keep the UL seams offset and staggered from the subfloor seams.

Even if I have plywood, not OSB? It looks like 5/8" plywood is the bare minimum...

I was talking about 5/8 OSB Dave. If your 5/8 plywood is a T&G subfloor grade, in good shape and pretty flat you can install 3/4 solid right over it. Your call on that.

OK I got you. I will use what I have then. Seems to be in good shape for the most part; minus one small ~2'x2' area. Don't know if I'll leave it; or cut it out and put down a new piece.