cubby wrote:
I've researched this extensively without a clear conclusion, so time
to reach out to the people who have probably experienced it.

I have a plywood subfloor that has several uneven parts. My plan is
to (1) level the worst spots with self-leveling cement; (2) add
another half inch layer of flooring plywood glued and nailed to the
joists. Then I will felt the remaining uneven spots as necessary, and
staple hardwood flooring.

The self-leveling products do not lend themselves well to plywood I
know, and it certainly doesn't seem recommended to add hardwood
directly over SLC. But I'm hoping that my "sandwich" approach will
work. I have previously dealt with such problems by shimming and
using varying layers of felt. But this hasn't always worked very well
- it's very difficult to deal with differences of more than a 16th or
so. In this instance I am looking at some differences as great as
1/2". I should add that the uneveness was caused by a previous
structural issue that has been fixed but that left a residual gap or
two.

Any thoughts gratefully accepted.

Are the underlying floor joists that far out? How large are these
places that are so bad and how large is the entire floor area. What is
joist spacing?

If there are really 1/2" low spots you'd be advised imo to use bulk
material to fill in the worst of the valleys if it's a sizable area.

There's no reason it wouldn't work although I'm not sure I wouldn't be
more inclined to fix/level the joists and lay whole new 1" T&G
subflooring instead; that being more so the larger the total area.

Think this is one would have to see/study to decide on actual plan of
action...

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