Well, I really "painted myself into a corner" on this one, and although I understand the difference between level and flat, I thought I could do both.

I wasn't sure how to proceed, so, since some of the joists just seemed to be lower, I decided to glue lathe to the top in some sections. In another section where the joist was sloping, I sistered them, making the sistered joist level.

I glued and screwed new plywood down, but the only plywood available was either thinner or thicker than the existing subfloor (thanks to the metric system), so I went with the thicker 3/4" equivalent.

I'm stuck now; I had planned on just adding thin plywood on top of what's left in this section, and then adding shingles and building paper to feather it out, but wondered if I could add 1/2" plywood and plane/sand it down. I imagine it would be difficult to even it out this way. If I cut out the last section of plywood, how would I deal with the joist that's on the other side of the wall - i.e.- what would I attach the new plywood along the wall to? (In the corner I actually installed an extra, albeit short joist).

BTW, the new plywood shown is almost perfectly flush with the old plywood on the other side of the room.

Yes, I am embarrassed, but hopefully my mess can be fixed.
http://www.mediafire.com/?08h0xfrmapuxr26,o6hp4e4h5aazlr0,csn3cmahgjcfhb8

Can anyone at least recommend a good book or instructional DVD to teach me the proper way. This is my first attempt at doing this.

I wish I could afford to hire someone to do it for me, but I can't, and daughter wants her room back.

I'm most embarrassed by the fact that I first asked what to do with the subfloor on June 26th, and this is as far as I've got.

Could someone suggest somewhere, anywhere, I could get the information I need, please.

Should this be on a carpentry forum? I just don't know what to do.

Sorry, Im a bit confused by the pictures, if im reading correctly the end of the new plywood is level to the old plywood at the end of the wall?

Thanks for the response.

No, what you see in the photos is what happened after I tried to level the subfloor without removing all of the old plywood, so what I'm left with is a section that is a lot lower.
The problem is the old plywood in the photo slants down, so if I just screwed, say 1/2" plywood on top, part of it will be flush with the new stuff I've put down, but most of it will be too high, and sloping. It's on the other side of the room that the new plywood (at least in one section) blends nicely into the old, although I have some issues there too.

I really think now, that if I ripped out the old plywood, I should have ripped it all out, and get all the joists at the same height. It really didn't help that plywood no longer seems to be available in the same thickness as when this house was built (late 1970's). It's essentially one ply thicker (or thinner). The big thing that I was scared of, though, is the transition at the bedroom door. I have enough hardwood to do all three bedrooms upstairs, but just wanted to get my daughter's room done first.

I'll try to get some more pics later that may make it more clear.

okay i understand a bit better, what is the difference in hiegt? I get there is a 1/2 in void next to the new plywood, what is it to make it to the edge of the wall 1/4?

OK, I bought some 3/8" plywood, and in this section you can see that along the wall it's almost the right height. That piece of shingle (or 5 thicknesses of 15 lb roofing felt) makes up for the gap along the new plywood.

Would it be OK to just screw down pieces of plywood like this, and then "feather out" the difference with shingles and/or felt? Most of the sites where I've seen them talking about using shingles, they then install another layer of plywood subfloor over it, whereas I would want to install a layer of the paper underlayment the flooring place sold me over all this, then the hardwood; would that be OK? I assume one would not overlap the shingles because it would make too much of a gap? Building paper seems like it would be better for "fine tuning" the thickness. Also, I'm a little concerned about the crunching noise from the shingle granules.

Now that I leveled most of the floor, the fact the the people that installed the newer sliding door installed it on a sloping subfloor accentuates the slope, but oh well. I guess that's one more reason it's more important to have it "true" than level. That door was really hard to open and close before though, and after I shimmed it at least it operates smoothly.

Again, I'm a bit embarrassed asking all these newbie questions, but if I don't know, I don't know, right? At least the subfloor is much more solid feeling, and squeak free now.

BTW only the larger new pieces of plywood you see are glued (using PL Premium) and screwed to the joists, the smaller piece is just glued (with contact cement) and screwed to the old subfloor.

http://www.mediafire.com/#rrt1z6avxg598

Edit: Silly me, I just realized, at least in this area, it is best to place shingles and/or building felt underneath the plywood, like this, right?
Of course, I would have to feather it out so the plywood has complete contact.

http://www.mediafire.com/imageview.php? ... 87e6s83y3n

Whats the water stains from? Are you overlapping the seams in the sheets, last pic looks like it isn't.

Funny you should ask; I was curious about the water stains myself, since there was even the odd rusty nail even in the middle of the floor. The only thing I can think of, and I see this all the time here even now, is when the house was built it was raining a lot before they closed everything up. The area I live in is a temperate rainforest (think Pacific Northwest). There are no pipes running through that wall, nor are there any signs of moisture now.

As for the seam, as shown in the photo, the 3/8" sheet just slightly overlaps on one side, and where the two new pieces join they are over top of the joist. Is this OK?

http://www.mediafire.com/imageview.php? ... 8wq840k6qc ....or should I buy a full 4x8 sheet (that was just from a 2x4 sheet) and do that whole section at once.

Am I at least grasping the concept of how to use shingles to flatten it out?

Nice discussion .. happy to commenting on this post ..Thank you

Yeah, I'm probably not the only one who's curious .

I forgot to mention that wherever i installed new plywood, I also installed full height blocking perpendicular(obviously ) to the joists under the seams.

There's nothing like trying something like this yourself to give one an additional level of respect for what the Pros do!

Unless someone tells me "STOP, you're doing it wrong," This is how I'm going to proceed:

First, I set the piece of plywood in the low section, and taking my 6' level, set it from the section of plywood that is already at the right height and flatness, across the low area.
Next, I took a piece of building paper, and while holding the level down over the "good" part of the plywood so it doesn't lift up, and kneeling on the plywood "patch" to compress it, slid the building paper under the level as far as I could, then took that distance as a measurement which I transferred to a sheet of building paper, cutting a piece out that width.
http://www.mediafire.com/imageview.php? ... 79&thumb=6
http://www.mediafire.com/imageview.php? ... p7&thumb=6

The first couple of times, the piece of building paper slid the whole distance, so I used the plywood patch as a template for a full size sheet, but of course, then each building paper sheet becomes progressively narrower.
http://www.mediafire.com/imageview.php? ... cz&thumb=6


Then I plan to screw the patch into the joist where I can, drilling pilot holes first.
http://www.mediafire.com/imageview.php? ... k4&thumb=6
I hope this is correct.

I did see a similar thing on HardwoodflooringTALK.com, but I didn't understand the process.

the first picture with the level with the felt paper under it, whats the thickness of the paper? folded 3 times over?
It looks pretty minimal from where I am sitting, probably could go right over it and never know

It's 15 lb paper, not sure what the thickness is. I was just using a single thickness under the level.
It's a bit deceiving because I had already added a couple of layers of building paper underneath the plywood in the first photo before I thought to document the steps.
Oh, and in the photo with the tape measure, I've actually reached the height I wanted. I think it was a total of 2 full size sheets, then two progressively narrower ones. Again, the photo was just a mockup for display at that point.
Maybe I'm being too anal about it?

edit: it's 3 full sheets, plus two narrower ones, and still just a tiny bit lower on one end. I used my vernier calipers, and the 5 layers works out to 5/32s of an inch.

BTW, I accidentally deleted some photos from a couple of posts, and can't edit them to put them back. Oh well, doesn't really matter I guess.