Hi

So we bought our first home a few months ago and have not been lovin it. It's a 50s ranch and we are putting in click lock oak flooring from a good company, but the subfloor over the crawl space is way out of level (1/2" in some valleys). The sub floor is 3/4" particle board (yes, particle board, not plywood) on top of 1x6s laid down at a 45 degree angle! So, I can't just put in sister joists cause the 1x6 is on top of the joists. Do I shim over the 1x6? Seems not so good to me and what do I use for shims just cheapo wood ones? Doesn't seem like a long term solution, so I'm considering tearing it up and replacing the whole subfloor system. Here are my questions:

1. What would a pro do?
2. Should I remove the 1x6 so I can do sister joists for leveling?
3. If I remove all the 1x6 my room to room transitions are all wrong, so how do I deal with that?
4. If I don't remove the 1x6, what's the best shim material to use?
5. What wood to use as subfloor? Particle board again, or switch to ply? T&G ply?

Thanks for any tips.

So you have 1X6's on top of your joist and then 3/4" plywood on top of the 1X6's? Is that right. I was not following your original post. Clarify that and I'll try to help you out.

HI there,
Yes, that's pretty much the arrangement.
Floor joists seem pretty normal, 1 x 7 1/8" but they are at 16" centers
On top of the joists are boards laid flat, diagonal to the joists. Just measured these and they are actually 1x7 3/8" (not 1x6 like I said before)
Then on top of that there is particle board (5/8" thick) - not plywood

The particle board is crap - lots of peaks and valleys - and I'm now planning on ripping it up and laying down 1/2" plywood over the 1x7 and then gluing and screwing it down with shims (to bring it to flat if the joists are also part of the problem) next week. Does this sound right???

Thanks in advance for any help.

Sounds like you are on the right track. The particle board is just a waste of height space, brings nothing to the plate as far a hardwood installation goes.
But since you are anticipating putting in a floating floor, it COULD remain in place. Ummm, why the floating system anyway?
If you decide to change to a nail down floor, use 1/2 inch plywood (or greater) levelling the base sub-floor first with a combination of wood shims, heavy paper, etc, install the plywood on top, and you have a sub-floor suitable for any type of installation.

Dennis is on the right track. Remove the particle board and leave the 1 x 8's. Then re-fasten the 1 x 8's while exposed. Those usually work loose over time and are quite noisy. Now is the time to re-nail. Using a 8' straight edge, locate the low places and high places. High spots can be sanded down. Fill in low spots with shingles and/or asphalt felt paper till the subfloor is flat. Cover the entire subfloor with 1/2" plywood, well stapled or screwed. Double check for flatness. Sand high spots if needed. Now you're ready to install your new floor.

Thanks for the help!

We're going with the floating floor cause it's got to match the other half of the house that's on a slab and the slab had to have floating B/C it had mastic on it that we didn't want to touch.

What kind of plywood should I use?

CDX, OSB? T&G?

I know nothing about plywood???

Thanks

OSB is not plywood, T&G is not necessary. Leaves CDX, lol.