A engineered wooden flooring 5/8" thick was installed over a old pine wooden floor that was not even. The recommended pad and even roofing felt was used with success in some uneven areas. There is a couple of areas where the floor gives or is spongy. This floor is designed to be a floating floor. Is there any suggestions for fixing these areas which are close to the edge (not in the middle of floor)beside removing and leveling the subflooring?
Sadly, I suspect you already know the answer.
A floating floor is only as good as it's subfloor. If the subfloor is not level, or soft, or damaged then it must be fixed before you can hope to have a decent floating floor installation. The only way to help a damaged subfloor without removing the new, floating floor would be if there are some soft or low spots AND if you have access from below. In this case, you could add brace framing that will raise and support the bad spots.
There are many other ways of fixing a bad subfloor - cutting out and replacing bad sections or skinning over everything with new plywood - But these will require that the floating floor not be in place.
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