How can I even out the subfloor for hardwood (3/4" oak) installation if one section of the house is lower than another section? The front part of my living room is higher than back part, a difference about 1/2" within 3 feet. I think this is because the front part is on top of the garage. I was thinking of using a 1/2" plywood for the underlayment on the front part and 3/4" for the back part. But then what should I use in between the 1/2" and the 3/4" plywood?

Also, there's a huge dip in one section (about 3 feet) of the living room with the lowest point of about 1". Should I remove the subfloor to shim it and put back the subfloor to level it?

Thanks in advance for any advice.

Hi
If it is possible to remove the subfloor to level it then this will defiinitely be the best way. Trying to level out a floor which has a gradual slope is very tricky - even if you laid down battens you would need to make sure each batten was the correct height to keep the flooring level.