Preparing Wood Sub Floors For Hardwood Floors

"Okay that's great but..what can I do to flatten out my wood subfloor? There are high and low spots here and there, especially where the plywood sheets meet." During original framing some floor joists may not have been straight or had a slight bow running the length. This will cause some humps in the final sub floor itself and should be corrected to insure you don't have a see-saw effect in your home. Any voids under a hardwood floor are also likely to create squeaks you don't want to hear.

Power Tools To Fix

One great tool that works well to remove minor high spots is the use of a flooring edger. If you live near one of our large home centers in the likes of Home Depot or Lowe's most of them will rent edger's for a four hour period or daily rate. Thinking of using a belt sander? Sure it will work, but the power of this tool can't be matched. Our picture shows a few plywood seam areas that were knocked down with 30 grit paper (also available with rentals). Another option is a power planer, but can be dangerous unless all nails are set deep enough not to be hit by the blades of the planer.

But We Have Severe Dips

If the situation is too severe, removal of the subfloor may be needed and attention to the floor joists should be addressed. However in some cases with major dips in a few areas, different thicknesses of plywood can be fastened into the valleys to create a bridge effect. For example; you have an area 36" wide and runs the length of one room along an outside wall. Let's say it slopes one inch. One could opt to install strips of plywood in the area in varying thicknesses so it tapers back to height of the rest of the floor.

Minor Dips and High Spots

In our next example we've encountered a high floor joist and an area adjacent to it that sags. Without corrections, squeaks are sure to be heard. The flooring edger knocked down about an 1/8" of an inch at the plywood seams (1) and we used #30 roofing felt (2) to bridge the low area then rolled out our standard #15 felt paper prior to the installation.

Another thing about floor prep before we continue. If you have any squeaky areas before the hardwood is installed take care of it before it's too late. Often plywood will loosen from the floor joists over time. Make sure they're snug. Decking screws work the best to keep both tight against one another.

Shimming

The better installers will view transitions areas with a keen eye. After all they will be the most visible in the home and there's nothing worse than a great installation but a failure to address these areas. Another example is an area that leads to ceramic tile. Our 3/4" solid hardwood will fall about 1/4" below the marble threshold. Caulk it? I don't think so. A simple solution is to shim with our #30 felt once again.

In this case we tapered back four layers of the #30 felt to bring the flooring up so the durock underlayment (under threshold) isn't shown. When using any material to shim it's important to taper back from all angles. Not shown in this case is the tapering we did on the sides of the felt. In order for this to work you have to create a gradual incline so the hardwood will engage properly by tongue and groove.