Since this topic comes up alot and there has been some misunderstanding and misinformation, I thought I would clarify it for you DIY'ers out there.
First let's talk terminology. It is importamnt when asking technical questions. So................
Subfloors......... Are the deck/wood floor a home is built on. The subflooring can be different materials and is always attached directly to the joists/trusses. Go in your basement/crawlspace and look between your joists. That material nailed to the tops of your floor joists is your subfloor.
Underlayment.............. If your have a vinyl floor in your home and you have wood subfloors, most likely you will have underlayment. Underlayment is used to provide a smoother substrate for some floor coverings, like sheet vinyl. It is also used to raise one area up to be even with another floor. It is used to provide a suitable substrate for tile ( like Hardi Backer Board) and used to stiffen the subfloor. It comes in many types: particle board, plywood, OSB, cementious tile backer board, sheet rock has been used, luan, masonite, etc. And more are being developed all the time. Underlayments are not subfloors and subfloors are not underlayments. Underlayments can be safely removed; subfloors should never be removed EXCEPT for damage or remodeling and only by licensed, knowledgeable contractors. Underlayments always go on top of subfloors and are usually stapled but can be nailed, glued, screwed, etc.

As far as wood subfloors go, this is what NOFMA (National Oak Flooring Manufacteres Association) and NWFA (National Wood Flooring Association) have to say. All solid wood floors should be nailed down (nail, staple/cleat) to an approved wood subfloor. Approved wood subfloors are listed in order; best to least preferable.This is based purely on the materials nail holding capability.
BEST: 1" x 6" solid #2 or better douglas fir or frame grade pine boards installed diagonally across floor joists 16" oc.
NEXT: 3/4" T&G Sturdi Floor plywood subflooring installed at 90 deg. to joists 16" oc.
Next: 5/8" T&G plywood subfloor installed at 90 deg to joists 16" oc.
Next: 3/4" OSB (Orientated Strand Board) T&G subflooring installed 90 deg to joists 16" oc.

There are other, older and not used anymore subfloor systems one may encounter. Such as: 1&1/8" T&G plywood subfloor installed at 90 deg to 4x6 beams spaced 4' oc.
1&1/2" x 5" T&G solid fir deck boards installed at 90 deg. to 4 x6 beams spaced 4' oc.
1x8 solid fir/pine boards installed at 90 deg to joists spaced 16" oc
1" RED-X T&G particle board subfloor installed at 90 deg to joists spaced 2' oc.
3/4" or 5/8" particle board found mostly today in modular and mobile homes.
These subfloors should NOT be removed but overlayed with 1/2" CDX plywood that is well stapled (2" around perimeter and 6" oc.) or glued or screwed. In all cases, subfloors and underlayments are to be flat to within 3/16" in a 10' radius.

When gluing down an engineered floor over a solid lumber subfloor, you will need an underlayment of 3/8" plywood, at least. When gluing down to a plywood or OSB subfloor, many are tempted not to use an underlayment. I prefer to use a 3/8" plywood underlayment over a plywood subfloor when gluing down a wood floor because if the floor needs to be repaired or replaced, it is easier/better with underlayment than with the subfloor.

I hope this clears up many of your questions regarding installing wood floors over wood subfloors.

Regards, Gary

Great post!!

Of course I need to follow up with a question.


What happens if you rip out an existing nailed/stapled floor and replace it with a new nailed/staples floor?

Will the tear out of the finished floor damage the structural integrity of the existing plywood subfloor? Will the nails/staples/cleats leave holes that then need to be filled or would you install a thinner underlayment prior to the new finished floor?

Perhaps it's not a concern?

Great stuff Gary. I never considered that one! I'm going to consolidate this message sometime this weekend into the sticky one I posted. Feel free to add any other comments.



I've never seen it as a concern, but I haven't dealt with as many plywood subfloors as the other guys. If large chunks are removed something should be done.

Removing a nailed down floor does not normally damage a subfloor to the point where one needs to replace or patch the subfloor. I've removed/patched many solid floors from wood subfloors and never once had to patch/replace the subfloor EXCEPT when someone glued the wood floors down to the subfloor. Then you can expect to damage the subfloor upon removing the glued down wood floor.