I'm sorry if you've all seen this question a thousand times, but after reading and reading, I'm still confused.

I have a 5/8" plywood subfloor on 16" OC joists. Then there is a 3/8" particle board underlayment on top of the subfloor.

I'm installing a prefinished 3/4" American Cherry 3" floor.

So let me get this straight... Should I *tear up* the particle board underlayment??? (I think the answer is "yes".) If so, should I put down a NEW plywood underlayment over the subfloor?? What thickness? How should the new plywood underlayment be installed - Nails, screws, glue?

I have taken out a piece of the particle board underlayment, and the plywood subfloor is in pretty sad shape. What should I do to prepare the subfloor? Or is it "no big deal" since I'll put a NEW plywood underlayment over the top of it?

Please help ASAP! I really wanted to start the installation of the hardwoods right away. But I also want to do it RIGHT!

Thanks in advance!
-brian-

You can lay your new 3/4" solid cherry floor right over your existing 5/8" plywood SUBFLOOR AFTER you have removed the particle board underlayment. You say the subfloor is in "sad" shape. It doesn't have to look good, just be structuraly sound. You may need to refasten the plywood subfloor in areas and screws work well for that. You'll need to run your new cherry flooring at right angles to the floor joists (90 deg.) Check for flatness and fix high and low spots. No need to install new plywood UNLESS the old subfloor is TOTALLY shot (by water or termites).

Thanks Gary! That's pretty much what I thought. I won't know just how bad the subfloor is until we get the particleboard off today, but I know some of it is splintering and has some holes in the top layer of the plywood. I don't have access to a flooring sander, nor would I want to take on that project! SO... Just how much time/energy should be spent on the subfloor. Should cracks be "filled" with something? Or would it be less time/energy to just put down new plywood underlayment?

One other hitch... I want to run the boards lengthwise down the hallway, which would be running them WITH the joists, rather than against them. With a 5/8" subfloor, will this be a problem?

As far as the height of the floor is concerned, it would match the rest of the house better if I DON'T have to put a new underlayment down.

I want to do this the RIGHT way, so thank you all SO MUCH for your help!
-brian-

Small gaps and cracks in the subfloor don't matter. Neither do small voids or holes ( note that I said small ). Running with the joists down the hallway could be a problem. It is not advised. Can you get under the house to add more blocking? If so, that's what I'd recommend. Don't fill the gaps between the plywood panels. They are supposed to be that way.

Gary said:
> Small gaps and cracks in the subfloor don't matter. Neither do
> small voids or holes ( note that I said small ).

Ok... that begs the question: How small is "small enough". Some of the voids/holes in the top layer of the plywood are as big as 1 x 5 inch strips, and about 1/8" deep (one layer of plywood). And there are some plywood corners that are splintered and a little deeper than that.

And what about high spots, where the top layer of plywood has a little wrinkle in it? Should that be CUT out, or sanded down lightly?

> Running with the joists down the hallway could be a problem. It
> is not advised. Can you get under the house to add more blocking?
> If so, that's what I'd recommend.

I can get under the floor in that area with ease. So should I put 15" 2x10s in between the joists in an "H" pattern? Just under that particular area of the hallway, right?

Or would it be better to just run the boards crossways across the hall, just like the rest of the installation. I don't recall ever seeing an installation where the boards weren't running lengthwise down the hallway! Does it look OK to run them the other way? What about the "ladder effect" that I've read about?

Thanks for your input!
-brian-