Recently bought a 33 year old home that has some significant settling
and very wavy subfloor. sub dips a good 1/4"-1/2" in some spots. We
were going to install HW but the installer stated the sub was so bad he
would not feel comfortable laying over it unless we got it fixed.
So...We got two estimates to fix which were about the same cost, $5k,
but we now have to decide what is the better way to go. Rip out and
replace the sub in all the rooms we are laying the HW (living, dining,
hall, master bedroom) or shim the exisiting sub and lay new sub over
the top. Here is the to do list for replacing:
Cut old sub floor around 1 1/2" from the wall
Remove old plywood;
Reinforce / level existing joists
Blocking joists in the middle
Install 2x4s on the perimeter to support connection between new sub
floor and walls;
Install new ¾ in. plywood (screws, liquid nails)
Fill gaps between new and old sub floor with "FixAll";

Any suggestions or comments on the best solution? We want to get to the
heart of the problem, but are afraid of what ripping and replacing may
lead to.
Also, anyone heard of insulating the flooring to reduce noise?
Replacing contractor suggested we do so, but was wondering if this is
necessary or recommended at all.
Thanks in advance for any help!