Filed Under Leveling Wood Sub Floors
Often in old houses it is necessary to level the wood sub floors before installing replacement flooring, especially if that flooring is going to be ceramic tile or even hardwood. If your wood sub floor is not level it will cause the surface of the new flooring to be wavy or, in the case of ceramic tile, can cause it to crack and fail altogether.
Before you can begin leveling your wood sub floors you must remove the existing flooring so you can access the wood sub floor. If you are not already familiar with this process you should read Removing Wood Sub Floors. You probably will not need to completely remove the old wood sub floor but the article has a good section on how to remove the original flooring materials. After reading that article, return here and we will begin the leveling process.
Now that you have the flooring removed and the wood sub floor exposed, let’s get about the business of leveling the wood sub floor. First you must determine why the wood sub floor is not level. This will require accessing the underside of the floor from either the basement or under the house. Check the floor joists and support beams to be certain they are sound and solid. Check any support posts or piers for settling, insect damage or rot. If you find damage or weakness in these structural items it is strongly recommended that you consult a building contractor to find out how big a problem you are dealing with.
After you confirm your structural support is sound you can begin to determine what need to happen to your wood sub floor to bring it to level. Often in older homes you will find a rise in wood sub floors caused by a floor joist with a crown turned up. This can usually be corrected by removing the wood sub floor and planning or sanding the top edge of the offending joist to bring it into level with the adjacent joists.
Sometimes the opposite is true. A wood sub floor will have a low area caused by a floor joist with a crown turned down. In this case it may be necessary to shim between the sub floor and joist to bring the wood sub floor to level. Take great care to be sure the joist has not been weakened by water or insect damage and in the process of failing. You certainly don’t want to go through all of this only to have to do the job again when the structure fails.
In the event of minor high spots at the plywood edges or cupping of the plank boards you can use a machine called a flooring edger. These are usually available for rent from large home centers and are worth their weight in gold when trying to level a wood sub floor with small high spots. You could also use a belt sander or power planer to knock down these high spots but you should be certain all of the nail or screw heads are well sunk before attempting to plane the surface. One small nail head could cost you a set of planer blades.
It is not unusual when leveling a wood sub floor to find low areas or dips next to the high spots. If you encounter these dips you should first shave off the high spots as discussed above then shim the shallow dips with 15# or 30# felt between the sub floor and the flooring.
Eliminating the highs and lows while leveling your wood sub floors will help to keep your new floor from squeaking in the future and give you a nice even finish. If you find yourself with questions not answered in this article or the archives feel free to contact us and we will do our best to get you an answer as soon as possible.