A flat subfloor is critical for successful hardwood installation. To calculate needs, use a ten-foot straightedge to check for dips and humps across the entire area. Measure the depth of any gaps using a tape measure or shims. If the variance exceeds the flooring manufacturer’s specifications, you must address it. Low spots can be filled with cementitious self-leveling underlayment. High spots may require sanding or grinding. Failure to level the subfloor can lead to hollow sounds, board movement, and potential damage to the tongue-and-groove system.
Ask an ExpertHardwood
How do I calculate subfloor leveling needs for wood?
Calculate subfloor leveling by checking for flatness with a long straightedge. If gaps under the straightedge exceed the manufacturer's recommendations—typically 3/16 inch over 10 feet—you must use a self-leveling compound or grind down high spots to ensure a flat installation surface.