Rookie_Remodeler wrote:
Hi!

Thanks for the reply.

"Upper floor" means the second floor. Removing the subfloor will not
help since the joists are sagged themselves. Therefore, I can either
fix the sag by adding strips of wood with different thicknesses or add
the self-leveler (not very keen on this one unless somebody chimes
in).

My concern about using the wood strips is that some of the wood planks
will be "floating", that is, will not be supported by the subfloor,
ergo asking what can be done in this case.


What you normally do is take the floor up and start planting and sanding
and cutting bits of timber up to fully level the joists.

Even better. gets some new (flat) joist and bolt them alongside the new
ones, with a level and a steel rule laid over their tops..or a string..

That will stiffen the floor a lot..