Subfloor below Hardwood...

[Greg Cuetara]

I have a second floor where we ripped up carpet and are putting down 5/8" bamboo. I got the carpet ripped up in one room and found 3/8" ply over 1/2" osb. The osb is not in great shape. The osb is nailed down to the joists and the ply was screwed down with 1" drywall screws. I pulled up a few pieces of the plywood and the osb looks like a nice little wave going down the room.

What is the recommendation for the subfloor below hardwood? Is there any way to salvage what I have...like maybe rip up the 3/8" and put down 1/2" plywood or should I really rip up everything and put down 3/4" advantech or 5/8" plywood?

I know one of the problems right now is that nothing is secured down to the joists really well so i was going to go through with long screws and tighten up the subfloor down to the joists anyways.

thanks,
Greg

[Jason Roehl]

If you really want to go to all the trouble to rip everything up, no one can stop you, but it's probably not necessary. If you do, I'd go with 3/4" T&G plywood subfloor.

If you can find where your floor joists are, I'd run some 2" construction (not drywall) screws through what you have into the joists.

Put down some 15# felt paper and use cleats to install the bamboo--staples will cause the tongues of the bamboo to split and can leave visible humps where the staples pushed the surface of the bamboo upward (just saw another contractor make this very mistake this past fall).

[Greg Cuetara]

Jason,
Thank you. I guess i'll run out tomorrow and get some good long screws and go nuts up there securing everything down. Good tip on using the cleats...havn't gotten that far yet. Taking down the popcorn ceiling, gotta paint that and then paint the walls then will be ready to install the floor.
Greg

[Mike Cutler]

Greg

Old house?
Is the "OSB" and engineered subfloor material, or did someone use cheap OSB exterior sheathing for the subfloor?
I don't mean to contradict Jason, but I'd rip it up, and have done so myself. Then put down the 3/4" T&G Jason suggested.
I put down a 3/4" T&G brazillian ebony floor on top of a layer of 3/4" Advantech, with a 1/2 Ply layer. The flooring was put down on top of Elastilon, and there is zero squeak, or flex, in that floor. I heat with a woodstove, so I may have gone a little overboard.;)

[Greg Cuetara]

Mike, House built in '83. From the looks of things they used the material they had on hand. Not sure the osb is a real engineered subfloor material but not sure there is a way for me to tell. When I pulled up the 3/8 ply the osb is all white...i hope it is not mold....

i would love to be able to take it up and put down advantech but really have to figure out if it will be ok as is rather than drop another 500 on plywood right now.

[Mike Cutler]

Greg

For me the decision was made by the house. Built in 1919 the floors had " New England charm" ( yeah right! ;).)
I had to rip up the whole floor, attach full width sisters to the joists, level everything, and then put the subflooring in. You are right, It was surprising how quickly the costs went up.
All of this because of leaking toilet flange.:mad:

Engineered subflooring has a lot of writing on it. Spec's and conformance detail for installation.

[David Larsen]

I would only replace the 3/8 plywood. Use construction adhesive and staple it down. If you are concerned about the OSB being secure to the joists, then secure the OSB to the joists prior to adding the new 3/8 plywood.

If you did take the OSB up, you have to take into consideration. #1. The cost. #2. The OSB is running under the interior and exterior walls. If you remove it and cut it flush with the walls you will alter the strength of the system. You can do it, but I would recommend putting some nailers between the seams.

The OSB is probably fine unless you have had some moisture problems. Make sure it is completely dry before recovering if you do.

The 1/2 OSB plus the 3/8 ply plus the 5/8 bambo will make it more than strong enough. The 3/8 ply over the 1/2 OSB will be strong enough to support the bambo.

[Jason Roehl]

Before we get too far into discussing the "strength" of various thicknesses of floors, first consider that the vast majority of carpeted, new-construction floors are on top of a single layer of 3/4" T&G OSB (and have been for 20+ years).

To match an existing floor, I have even installed 3/4" red oak flooring directly onto the floor joists (with felt, of course). It was plenty solid.

So whether or not the 1/2" OSB is in good shape is really irrelevant, as long as it is not wet and moldy. Get the 3/8" plywood solidly connected to the floor joists, and you'll have a solid purchase for the cleats.

[David G Baker]

It is possible that the white stuff on the OSB is from plastering or from Sheetrock installation or mudding and probably not mold.

[Jim Becker]

... 3/4" T&G plywood subfloor..

This. Over the OSB...which will be nearly impossible to remove cleanly. And no drywall screws!!! Us proper flooring adhesive (there is low VOC available for safety since your home is now finished with people and, perhaps, pets resident) and then nail.

[David Weaver]

I would do the T&G ply subfloor, too. It is what is in our 60 year-old house - or something similar, some sort of joined ply.

My parents' house is circa 1924, and the subfloor is a second layer of (presumably ugly, it's painted on the bottom so hard to tell) hardwood floor either running diagonally or 90 degrees to the to layer of floor. i can't remember exactly which, but it "talks" quite a lot as you walk across it. You'd have to be a pretty heavy sleeper in the house to ever get robbed without waking up.

[Larry Edgerton]

Because it is absolutely certian that it is going to rain on a new house here I have been using the newer waterproof osb products for subfloor. Most flooring manufacturers do not warrenty their product if installed over regular OSB, but do over the premiums. You are not going to get wet but for me delamination problems made me switch.

In this case I would screw down whatever you decide with a good screw as Jason has suggested, I use GRK's. Glue of course. I would hesitate to have three layers though. Too much chance of something not being tight, but it is hard to say having not seen what you are looking at. Just the fact that they used 1/2" osb makes me question whether anything else was done correctly.

Larry