How to Prevent Uneven Floors

What You'll Need
Replacement lumber
Construction adhesive
Wood screws
Level (laser level is best)

Preventing uneven floors is the first step in any flooring project. Whether you are installing hardwood, tile or laminate flooring, if the floor is even slightly uneven your new flooring will not perform as well or last nearly as long as it should. It may also result in bounce or squeaks in the floor. It is entirely worth investing a bit of extra time and money to make sure that floor is even before installing flooring. Here is how to ensure you get an even floor.

Step 1: Inspect Existing Joists

You will want to inspect the existing floor joist for rot, damage or decay. Some may just be old and need reinforcement. Replace any floor joists if needed, or reinforce the existing floor joists. If there is obvious sagging in the existing sub-floor, you may want to consider adding support beams for additional support. In many homes, particularly old ones, floor joists could be spaced too far apart or are not sufficiently supported for the required load.

Step 2: Evaluate Sub-floor

The sub-floor is usually of plywood, and is also subject to decay and rot. If this is an existing sub-floor, evaluate the wood to see if replacement is indicated. If in doubt, replace it. The plywood is critical to the amount of flex in the floor, which can compromise the integrity of the flooring above it if there is too much. Sometimes, all that is needed is some additional strategically placed screws to secure a particular spot. Make sure that screws are not placed immediately next to seams between plywood sheets, but in the body and straight into the joists. Construction adhesive can also be helpful to add some additional reinforcement to a troublesome spot. Ideally, particularly for tile floors, tongue and groove plywood is best to eliminate any flexion around butt joints of sheets.

Step 3: Evaluate Floor

Check the floor at different points in the room with the level. Assess the floor at different angles and identify any uneven areas. There are a variety of ways to even the floor, and a broad spectrum of ideas and suggestions can be found on the Internet. However, there is a common opinion that the solution is shims (on top of existing sub-floor) and additional plywood can help even spaces out. That is, assuming, that all that can be done to correct uneven floor joists has been done. If the area that is uneven is low, it can be built up using shims cut from a 2x4 with 1/2 inch plywood over the top. If there is a particular area that is raised, screwing it more tightly into the floor joists may correct the problem.

Step 4: Evaluate Flooring

Flooring can also cause uneven floors. Warped hardwood will create ridges in the floor. Laminate can bubble up. Tile can break. If any of these are the culprit of the uneven floor, it can be corrected by replacing that particular section of flooring.