" floor rises approximately two inches from the middle of the house to the end."

Over what distance?

The important thing is that the floor is flat. It can be unlevel (i.e., the bubble in the level is not centered) as long as it's on an even angle across the whole length (i.e., not "wavy").

So if it's flat, you can install hardwood without doing something to the subfloor. If it's not flat, you have to remedy it, but how and how much depends on the nature of the "waviness."

I was worried about this because we wanted to put hardwood in a 50-year-old house. So I bought unfinished hardwood. The installer was able to sand the surface down to disguise any irregularities in the subfloor. Turned out great.

brickeyee - That's a hard question to answer. I think the answer is the change happens somewhere over about 21-22 feet. But, the tricky part is I don't know if it is an even gradient. My thought is probably not, but that it is masked by the change in flooring type. For example at the thresh hold from the kitchen to the dining room you can see the change in elevation.

Get a laser level and set it up about 4 feet above the floor.

Now walk around with a metal ruler and map out the dips and rises in the floor.

you cam even sue chalk to write numbers on the floor at various spots.

You can them go back with tape measure and see how far apart the dips and bumps are.

Smaller changes (say 1/8 inch) over a decent distance (8 feet) should not be a problem.

Even 3/4 inch t&g floor has some flex.

You may have to use more than the minimum nailing schedule.