Hi,
I am close to finishing a remodel project and installing the flooring is my next step. I checked the subfloor for flatness and found that my new subfloor is out of plane with my old subfloor. The two subfloors meet at the same elevation, but they are just on different planes.

I'd like to raise the old subfloor gradually up to a 1/4" at the back wall (think wedge shape). I've read that roofing shingles are OK to use in this situation but I want to make sure it is the best fit for my scenario. I have left over starter shingles that I can use to gradually raise the old subfloor elevation, and I have 15 roofing felt to help smooth the transitions.

I will be using 3/4" oak flooring and it will run in the direction shown in the photo (see the one strip laying on the ground). This isn't ideal since my joists run that direction, but I didn't want the plank subfloor running the same direction as my finished floor.

I would rip out that little bit of planking shim the joists and install more OSB