I am trying to prepare 60 year old 3/4" oak tongue and groove floors for new 3/4" Santos Mahogany replacement flooring. Unfortunately I have had to remove a few walls and the old duct work so the oak hardwood floors, which are still in very good shape, cannot be spared. I want to apply the new flooring over the old oak but found that there are some low spots where the old supporting walls have been removed and replaced by overhead beams. I have patched the floors where the walls were removed but there is a 0 - 1/4" depression in the floors adjacent to where the walls once were. I considered using a leveling compound, such as laticrete but it does not state that a hardwood floor is a recommended substrate. Does anyone have any suggestions for a solution? I also considered using some type of shim but have never done this and have no idea what material to use and how. Any suggestions would be most appreciated. The area where the floor has depressed over time and where the walls were removed are about 4 feet long and a foot wide. In the middle of the 1 foot width the depression is about 1/4' and would taper to 0" within 6 inches to either side. The new flooring runs perpendicular to the four feet section that was repaired.

Four feet long
____________________________________________ 6" from center line it is back to flat

____________________________________________ Center line is depressed about 1/4" - the is the middle of the area where the wall was removed and the floor patched with 3/4" board, screwed and glued.

____________________________________________ 6" from center line it is back to flat

Thanks,

Edgewater

First off, if you plan on going over the existing flooring, you will be going the opposite direction, or at a 45º angle, or you will experience some serious seasonal movement.

A band of ¼" ply or OSB as a shim in the low area and taper back batting wedges on 6-8" centers.

If I lay the new floor opposite the existing floor, it will run parallel to the underlying floor joists. Will that result in any problems. The house is 1930s vintage so the first layer of subfloor is made up of 7/8" thick by 6" wide tongue and groove planking followed by the 3/4" thick oak tongue and groove flooring running perpendicular to the floor joists.

If it already has a 1x6 subfloor going across the floor joist, the oak is laid the same direction of the joist, and across the opposite direction of the 1x6 plank subfloor. At least that is how it should have been done.

No matter which direction of the joist, the rule is to go the opposite direction of the wood your going over and fastening to.

You should be able to find 3/4 unfiniished oak and repair and refinish the entire floor, but if not the osb and shins is they way to go. Good luck!

Can someone provide me with a little more detail about the use of batting wedges as described in the post by the flooring guy? I am not familiar with this description. Thanks for all of the feedback. It has been most helpful.

A tapered cut 2x. A long wedge shape.

The height you need, tapered back to zero.

Laid like a simulated joist, but on top of the existing wood floor, or any substrate.
Placing them close together @ 6-8" centers so you can lay the flooring across them and have full support.

Or in this case, to support plywood so it is level with the existing flat substrate and the flooring on it.

It depends where the low area is and the depth it is.