Leveling subfloor before engineered hardwood

[martyInVA]

I would like to have all the carpet and vinyl flooring on the 2nd floor of my townhouse replaced with engineered hardwood. In front of the kitchen sink, the floor sags about 3/16" between the joists. Under the refrigerator, the floor has also dipped where the wheels rest. This is a common problem in my development and I'm aware of houses where hardwood was installed without replacing the subfloor, and also some severe cases where the entire subfloor was replaced.

At what point does replacing the subfloor become necessary, and what is an acceptable method of correcting the problem when it's not necessary?

 

[Jadnashua]

You need to carefully read the installation instructions for the material you're interested in installing. I had a similar (but more severe) situation in my townhome where I wanted to install an engineered wood floor. It ended up being a major endeavor. I literally tore up all of the subflooring, leveled the joists which in some cases required plaining them, and in others sistering or shimming, then installing new subflooring. The end result was a very flat floor. On the stuff I was installing, they wanted 1/8" or less variance in 10'. About the same industry requirement to install new tile. It sounds like they skimped on the subflooring thickness, allowing it to deflect more than it should. Not an uncommon situation, but kind of sad.