There are several problems that can cause a sagging or sloping floor which is one of the reasons why fixing a sloping floor is difficult.
How to fix sloping floors on second floor.
Except for that slope the floor itself might be flat.
Load bearing wall removed or altered on first floor.
Sagging floor issues often relates to framing issues or the loads that the floors are carrying.
Foundation issues deteriorating wood supports especially sills which rest on the foundation footer improperly installed joists or sub floors and other issues can all cause a floor to slope or sag.
Common reasons for sloping or sagging second story floors.
Depending upon the conditions it is possible to strengthen or repair existing framing members such as floor joists or roof rafters by adding reinforcing material sandwiching the member on either side with plywood is sometimes worthwhile but the plywood must be installed correctly for greatest strength.
For rooms that have a general slope the issue may be foundation problems that require the assistance of a foundation repair company or a general contractor.
Before embarking on the floor leveling project here take a simpler approach first.
The cause of these may be the same or may be different.
If a load bearing wall is removed on the first floor then the second story floor joist or trusses may drop down in the area where the load bearing wall was removed.
Thre ways to fix a sagging or sloping floor.
Slanted floors can also cause cracks over windows and doors or make doors and windows stick and tough to operate.