Subfloor difference due to addition, how to fix?

[EllenEL]

My house has had addition built to it 20 years ago and hallway has a hump in the floor. I am looking for best solution how to even it out. Of course I can always put carpet but am hoping not to as I do not like carpets.
The difference in floors just under an inch. Hallway itself is 20' x 3 ft and connects multiple rooms including open floor LRDR and kitchen. So simply adding more plywood in old part will influnce a lot of floor difference in other parts of the house.
I am planning to instal Kahrs floating floor in all bedrooms and LR DR , kitchen.
My kitchen cabinets being delivered and I really have to figure out height of the floors so I do not mess kitchen instal. Couple of kitchen cabinets are goingnto the ceiling so I am really in trouble if I did make mistake.
Old part of the house is OSB 3/4" and new part plywood.
I am hoping to install over OSB as there is current laminate flooring over LR DR kitchen which successfully stayed there for 30 years.

 

[Mark Brown]

Is it located just in a hallway, like a localized area of joining? If that is the case just open it up 6 feet back or better and plane it down.

 

[EllenEL]

Yes, rest of it are in rooms/walls so I guess more stable or less noticeable.
Am not sure I understand, it will require lifting up current plywood piece of hallway, cutting what is under to the difference and reinstalling plywood back?
Additionally now that I think of it while sticky tiles seems to come off reasonably easy not sure what to do with residue on OSB? Thankfully it is only in hallway.

 

[Mark Brown]

Yeah, that is what I mean. Depending on where it falls it is usually the best/only option.

There aren't a lot of cost friendly or height friendly options available. If you can't fix it at the joists, it just gets ugly.

 

[EllenEL]

Thank you!
It needs to be investigated then. I am not sure if it will look good but I was thinking of putting some form of transition/ reducer piece in between and pretending it was design all alone?