What is under the particle board?

Usually, the same thickness as the particle board.

If you have a wood subfloor, after you rip up the old particleboard, lay down 15 lb felt paper (if you don't already have it down), and then replace the particleboard with plywood of same thickness. I think our installers used 3/4" BC plywood. (one side was "nice") They left about 1/2"-3/4" gap between it and the drywall, which will be covered by your base trim anyway. Usually your drywall will stop about 3/4" before the subfloor too.

If you have a concrete floor/slab, let a flooring expert on here answer your question. I have no idea on that one.

Also, most of the solid wood flooring sites have good information about installing 3/4" solid wood floors and subfloor prep, as well as the National Wood Flooring Association (google that one).

Hope that helps and good luck!

We just did this very same thing in Nov. We used 3/4" T&G Advantech. It is something similar to OSB. It has a 50 year warranty and is supposed to be superior to plywood. We placed it at the edge of the existing drywall, which left room for expansion. A contractor I know wanted $1400.00 for labor and we supply materials. Our space was about 900sf. We had never done anything like this before but are glad we did. Big savings for these diy-ers.

Thanks for the responses everyone.

Under my particleboard subfloor there is a plywood floor.

sippimom, you suggest I lay 15 lb felt UNDER my new subfloor. Is this in addition to the felt which traditionally goes ABOVE the subfloor (and under the 3/4" hardwood planks)? Or if I do this do I no longer need the felt above the subfloor? What is the rationale for moving the felt down one layer?

> I'm curious as to why you need to add another layer of plywood if you already have 3/4" plywood under your particleboard?

Under the particleboard is a plywood sub-sub floor that runs completely under the walls. I was under the impression that you weren't supposed to nail hardwood floors directly into this, otherwise what's the point of a subfloor?

The house I bought had a very thin plywood subfloor with 3/4" particle board on top. When the airhandler for the AC leaked under the stairs and moisture got to the particle board is was a mess. Particle board crumbles when it gets wet. We had to tear out all the flooring and replace the particle board. That is where the 3/4" T&G came in. We also put 15 lb felt between to help serve as a moisture barrier. It also made the floor very sturdy & solid.

urungus, you need to determine what your plywood subfloor is. What grade, how thick, and is it tongue n grooved. Most times that will be a CDX sheathing grade , less than 3/4" thick, and will be a squared edge instead of T&G.

Find all that out and report back :)

I am doing same thing -- removing carpeting from particle board surface to install 3/4 in hardwood. I have 15/32 plywood under the particle board.

Several contractors and flooring experts ALL state the particle board is NOT suitable for nailing h/w flooring.

Consensus is that removing it, and placing an additional 1/4 luan or 3/8 plywood will provide satisfactory base. This would be total 3/4 inch -- manufacturers specs are minimum 5/8, hence my 15/32 is not enough.

Thats right, in most cases the first layer will be 15/32 (1/2") CDX sheathing grade plywood.... only thing that is good for is roof or wall wall sheathing. It has no T&G either. I would not go any less than a 3/8" BC grade plywood underlayment... a 1/4" would be a waste of money imo.

I prefer thicker underlayments ... 1/2 or 5/8 BC plywood. It depends on what the finished floor is going to be.

I have run into a similar situation at my house. We have 1/2" CDX plywood under 5/8" particle board that previously had carpet installed over it. I've finished removing all of the particle board in preparation for installing 3/4" solid oak flooring. My contractor said it would be OK to use 7/16" OSB on top of the CDX as an adequate underlayment. What are everyone's thoughts on this? Should I just spend the extra money to put down 1/2" plywood instead?

It will work but you won't see that in the NWFA or NOFMA manuals. I use a BC grade plywood... I'm looking for holding power and stability here, plus, I am getting paid to do the best job i can for my clients.

"I am getting paid to do the best job i can for my clients."

Heard dat!!!!

Don't cheap out on the prep!! The prep is basically the most important part of the job. Have you thought about angling the installation, on a 45º????? You won't have to overlay any plywood underlayment, unless the substrate has an enormous amout of movement.

Yeah you do Floorguy.. it's only a 1/2" CDX square edge plywood sheathing. That's not suitable for any kind of finish flooring without adding some type of underlayment.

Oh, I thought I read ¾. In that case the substrate would have an enormous amount of movement!!! Only me and Jerry could walk across it.

I am the proud owner of a new (to me) 1984 home that had carpet over what appears to be 3/4" particle board. I was reading on some of the other hardwood sites that I cold just install 1/2" CDX plywood over the top of the particle board and that would be adequate for installing 3/4" solid hardwoods. I'd definitely glue/screw the plywood. What do you think? If this is not a good idea, what should I do? I appreciate the help!!

We have a 1975 mobile home which has water damage in the kitchen (a valve leaked under the kitchen sink. The floor now 'gives' at the door and along the kitchen cabinets. I need to replace the particleboard floor in the kitchen and have some soft spots in other areas. Do I set a saw at a 3/4" depth to cut away the damaged flooring and replace with 3/4" plywood? Some has been replaced in a bathroom, but the whole bathroom floor needs to be replaced as well.

@marcus, I know this thread is old, but we're in the same boat. Did you end up going with the 1/2" plywood on top? Did it work? We're looking at a $10k quote for removing the particle board, it would be so much cheaper and easier to just put the layer of plywood on top.