| we are installing 3.25" wide x 3/4" tongue/groove rift and quarter sawn red oak - nail down, site finished. Our floor is 12" floor joists, 16" on center. 1/2" plywood on top of that needs some work. We will install 3/4" plywood on top of the subfloor. Followed by oak flooring.
We have two "dips" in the 42" hallway. One case the joist feels a tad "high" and there is a 1/4" dip about 2 feet away. The other case there is a low spot about 3/8" deep - again about 2' from the higher spot.
question - I think I need to flatten out these dips before putting on the new 3/4" plywood. But how? Because they are in the hallway, I can't really take off the subfloor and plane the joist - I can't get that close to the wall. Should I use some sort of self leveling cement? But - it must remain flexible - I don't want it crumbling apart after a few years. I've also heard of people putting down roofing felt - but 3/8" is alot of layers to put down! Again - will it crumble over time?
Maybe instead of planing down the joists, I need to "raise" the joist a bit by sistering on another board that is flat across the low area and then secure the subfloor to that new "raised up" joist.
Thanks in advance for your suggestions! | 
