My subfloor is 3/4" plywood with 3/8" particle board ontop. From everything that I have read I need to remove the particle board, but should I put down some 3/8" plywood (or thicker) to replace the particle board, or can I put the hardwood directly on the 3/4" subfloor?

Wade

Your subfloor is approved by NOFMA and the NWFA. No need for underlayment as long as your flooring is being nailed down, the joists are 16" OC and you install at 90 degrees to direction of the joists.

In response to the question about replacing the particle board subflooring with plywood, you wrote the quote above. But I just found this:
"The more preferred type of subfloors would include those mentioned above. NO pressboard or particleboard." [found at http://www.hardwoodinstaller.com/hardwo ... floors.htm]

I have 3/4" particle board subflooring (over 1/2" plywood subfloor!) and don't want to replace it for my 3/4" hardwood flooring installation. Is what I found an opinion? Does NOFMA and NWFA say particle board subflooring okay?

All wisdom on this is appreciated! Thanks.

You are making a commom error in refering to underlayment as subflooring. In my quote, I said the SUBFLOORING is approved, which it is, being 3/4" plywood. Your situation is different. You have thick particle board UNDERLAYMENT over thin plywood. The proper way to proceed is to remove your particle board UNDERLAYMENT and install 1/2" plywood. Read this.
http://www.hardwoodinstaller.com/hardwo ... .php?t=385

VERY HELPFUL. I think all my questions have been answered, BUT ONE QUESTION REMAINS. My 3/4" particle board underlayment extends (obviously) under the wall drywall. I assume that the nailing of the particleboard underlayment was done before the drywall went up. How best do I remove the underlayment when it extends under the drywall? I'll also want to replace the underlayment with 3/4" plywood. My first instinct was to take a circular saw and cut around the perimeter of the room, but then I realized that it would leave a bit of the particleboard under the drywall and sticking into the room a bit. I hope my question is clear. Thanks. You've been very helpful.

I CA., this never happens but I hear it is quite common in other parts of the country. Where the builder uses wimpy 1/2" plywood subfloors and then installs 3/4" particle board over that. For the life of me, I cannot understand that reasoning when that builder could have simply installed 5/8" or 3/4" plywood and been done with it. Anyway, are you SURE that the particle board extends underneath the wall framing plate. Cut the sheet rock up about an inch in a few places to check. If the walls are built on top of the particle board, and you want to install a solid, 3/4" nailed down wood floor, then you need to remove that particle board (but not from under the walls, of course) It's either that or switch flooring products. Or you could risk it but you flooring with experience excessive movement. Keep in mind that one rarely nails more than a few inches close to a wall so you could skill saw out the particle board leaving that last few inches and replace it with 3/4" plywood. Or remove ALL the p. board (except whats under the walls) and install 1/2" plywood. You figure out whats better. More money for 3/4" ply but less work; or more work and less money for 1/2" ply. Take your pick.

Photos are better than my verbal description! Please go to
http://www.gfmuiuc.net/underlayment/
and see what I did after your last post. I cut back a portion of the particleboard underlayment and it was quite stuck under the drywall. But sufficiently crappy to be able to be picked away.

See photos and that should help you understand my situation. Thanks. You're being a huge help.

My floor is 1/2" plywood subfloor with 5/8" particleboard underlayment. I've resigned myself to pulling up the particleboard and putting down 3/4" plywood underlayment (which is pricey). I do want the floor to be solid, but oh the dust and hard work to remove and install!

As to your question, I don't know. But in a reply to one of my questions, I received this link that you might explore--capture the whole link and not just a part of it.
http://www.hardwoodinstaller.com/hardwo ... .php?t=385

I went to a good Lumber Company (not home center) and asked what they recommended for UNDERLAYMENT (not subflooring). They said all the homebulders are using T&G OSB for underlayment for hardwood applications. But after reading the sticky (which didn't actually say which Underlayment to use--only which Subflooring) I think I'm going with the 3/4" T&G Sturdi Plywood after removing the particle board. The other plus with using a Lumber Company is that while they charge a bit more per sheet, they delivery is free. Thanks for your help.

David , you should use a square edge for that and not T&G. Anything used for an underlayment should be sq.edge regardless of the product. the lumber yard did not understand your question I don't think. Remember you have walls in the way now.

Thanks very much for your quick and helpful response. I explained to Lumber Co. man (an older man who said he was in the construction business) exactly my entire structural situation (layer by layer) and it that it was the underlayment I was replacing. I don't think he knew what he was talking about.

The Sticky I read was a bit fuzzy (for newbies like me--its target audience) about what Underlayment to use since it focused so much on subflooring. As I've dug through this great website, the real questions we newbies have is about UNDERLAYMENT and NOT subflooring. (One poster e.g. thought that if the subfloor was plywood and the underlayment was particleboard that the 2" staples might be used to put down the hardwood. But still, the particleboard had to go. And I saw in the Sticky the list of preferred subflooring and decided on the 3/4" T&G plywood for the underlayment, since it didn't list the preferred Underlayment. You saved me )

I think I finally have all the information I need! I'm so glad I joined this website. Thanks.

If you read it carefully, it mentions TWICE that CDX plywood is recommended for underlayment. CDX plywood is NOT T&G and is a lower grade perfect for HARDWOOD underlayment. This is where it mentions plywood for underlayment.

Yes. I saw that (I didn't know what CDX plywood was or that it was specifically not T&G). I only was thinking that the Sticky would have been improved by having a list of preferred Underlayments, which is what so many of us need to learn about, especially since we were warned in the Sticky not to remove the subflooring unless it needed, and then only by professionals. I liked the Subfloor list of most preferred to least preferred materials, but wanted such a list for Underlayment. Thanks!

The fact is, no "list" is needed as the ONLY recommended underlayment for hardwood is plywood. So what would that list include? Plywood, plywood and plywood. Now there are various grades of plywood with CDX being almost the lowest (and cheapest). But it performs it's function as an underlayment perfectly. Also, in many cases, underlayments are not needed or required. Only when there is a flawed subfloor. Then it is needed and the sticky pointed that out quite clearly, IMO. It also listed many types of underlayments that are used in construction but most are not suitable for hardwood flooring. But I'll take it under advisement to improve the sticky recommendations. Thanks for your critique.

I returned to the Lumber Company to price the CDX (3/4" is $19.95). They maintain that "industry standard" is OSB for underlayment for hardwood flooring applications. The guy I spoke with said, "I know that 99% of the builders of the finest homes in town use OSB under the hardwood floors." Ack! We visited The 2006 Showcase of Homes--new gorgeous homes by various builders who were there to greet the hundreds of people who parked in the nearby newly converted cornfield. I looked at the hardwood flooring very carefully in each of the showcase homes (Champaign, IL prices ranging from $387,500 to $425,000). A Dutch graduate student went with and he said each of the homes would have been easily over 1,000,000 euros in Holland. In several homes some woodflooring areas that were not flat. And some of the end pieces didn't meet. But most of the flooring in the homes we saw was gorgeous. I haven't a clue what subflooring or underlayment nor how it will fair as the first cold season passes.

I need underlayment to replace what's there now (particle board to be removed), to stiffen the subfloor, and to bring the final floor level up to match the newly tiled adjacent rooms.

Part of my confusion over the OSB issue is that the "NOFMA Installing Hardwood Flooring" PDF someone sent me says that 3/4" "OSB is a comparable substrate" in their "Installation over Wood Joist Construction" section (p. 4). NOFMA has OSB subfloor covered by tar paper and then the 3/4" flooring nailed down. They said if this is over a crawl space (my application) to make sure it is vented and there is a plastic vapor barrier over the ground of the crawlspace. But I keep remembering that subflooring is not underlayment (which I now take has to be plywood).

I tend to read info from the point of view of a complete novice in this area and things obvious to the experienced are not so obvious to some of us. Thanks for all your help and patience.