Sloping floors are aesthetically unattractive and uncomfortable to stand and walk on. This problem can be solved with some simple steps.
1 - Foundation Repair
Inspect your foundation for any structural problems such as cracking or sinking. This type of problem will have to be resolved first. You will need to consult with a contractor for the best solution to your problem.
2 – Shim Installation
Shims can be positioned between the sub-floor and the joist. This should level out the floor of the room. Use a level to be sure the floor is sitting properly then nail the sub-floor through the shim and into the joist
3 - Self-Leveling Compound Application
Apply a primer to the sub-floor to make sure that the compound adheres to the sub-floor. Allow the primer to dry then apply the self-leveling compound. Begin at the lowest part of the floor. Carefully spread out the compound to create a flat, level floor.
4 - Floor Joist Replacement
Weak and poor-quality floor joist will not provide the necessary support to a sub-floor. Inspect your floor joists for any damage or weak areas. If you find any evidence of problematic joists, have them replaced.
5 - Sub-floor Replacement
Inspect the sub-floor from underneath for any evidence of sagging or damage. If you find any areas that are damaged, have them replaced. If possible, install a vapor barrier to prevent any further moisture damage.
Source: www.DoItYourself.com