If your floors are uneven, find the high and low spots. This is one of the best ways of determining if a foundation problem is causing your floors to be uneven. Sometimes foundations that need shoring up may cause certain areas of your floor to bulge or buckle, so make sure to closely examine each and every section of your floor.
If it seems like an area is sagging, take a sharp knife or razor blade and insert it under the sagging area. If it can easily cut into, or cause slight indentations, then there’s a good chance that you have found the place where your sub-flooring has rotted through and is causing your floorboards to bow.
It is important to find installation problems before your floor is completely installed. There will always be areas where you’re working off the floor, so before you put the final touches on a level floor it’s best to find and save yourself from any sags or dips.
Dips may also be caused by an issue with joists and beams below your floor that require shoring up. If you have a laser level, use it to check for sags or dips in the floor. Many different types of levels can be used horizontally or vertically and they are fairly affordable. Another option would be to secure yourself a set of carpenter’s spirit levels. These give very accurate readings and are much cheaper than newer options such as laser levels.
Solution:
Use Self-Levelling underlayment: Pour self-levelling underlayment is used to level out high and low spots so a concrete slab can be poured, making sure no low or high-spot areas remain. A growing number of home improvement companies are now using self-levelling underlayment as an extra service to their customers.
Attempt Sistering The Joints: If you have access to the basement or crawlspace, it is possible to jack up saggy joists until they are level and then sister them so that they remain straight after the jacks are removed. Sistering is the process of mating up two boards with bolts, nuts, and washers so that the new board corrects or supports the other, weaker one.
Replace Columns: A column fix replaces broken or damaged concrete floor columns. Concrete supports floors, but sometimes these concrete supports can break or become damaged. For example, a dirt floor basement floor may have a hole in it, and the columns that hold the floor up will need to be replaced. The new column will need to be installed in a way that keeps the floor from sagging while you finish the basement project.
Add New Wood Floor Coverings Over The Affected Area: If you can put new wood over the old, that’s great. If not, follow the advice above for fixing wavy floors. There are many fixes for a wavy floor, and you have already identified a solution or two that could work for your situation. You may need to add more hardwood joists, or you may be able to add plywood and get by with lighter floor coverings.