Your floors have to be even and flat. Unless they were designed to be sloping or with a gentle incline, floors are normally made to be flat. Foundation cracks and other problems below the house show up as symptoms in many ways. One of them is sloping floors.
How to tell if your floors are sloping?
The issue with sloping floors is that is is quite difficult to actually know or ascertain when it moves. The move may be too subtle to readily identify and it is too slow to see happen. For the most part, people tend to see or feel sloping floors only after it has moved considerably and by then the foundation cracks are apparent.
The easiest way is also the most obvious- set a ball on the floor and see if it rolls. A steel bearing or a large marble works best. If you doubt the ball’s movement is not reliable, try it from different points in the room and the adjacent room and tape the path, are they all pointing to the same direction? A more accurate method will be to use a spirit or bubble level that is at least two feet long. Place it at different parts of the room and make a note of the points where the bubble stops, if it is not in the center, the floor is sloped. If you have a laser leveler, it will be a lot more accurate.
So you have uneven floors…
The first thing to do in such a situation is to find out if the issue is just a cosmetic failure caused by bad workmanship or a result of foundation cracks. Follow the slope and see where it ends or find the deepest end of the bow, go directly below it to your basement and see if the floor at that point is also sloped. If it isn’t then it is a localized issue, if not and the basement is also bowed out, it may be a foundation issue. Call in the professionals and let them figure out how to fix it. If caught early, it may not even be that big a deal to repair. The issue of sloping floors is more common with slab foundations than with other types.
While this issue can be repaired and the damages rolled back, it would take a lot less time and cost way less when caught early on, that way further foundation cracks can be prevented as well.