Q. Can moisture condense on the back of a prefinished hardwood floor above an uninsulated crawlspace and cause cupping? The flooring was installed over 15-pound asphalt felt and an OSB subfloor; poly covers the ground underneath the dry and ventilated crawlspace of the 2-year-old home.
A. Tandy Reeves, a certified flooring inspector and CEO of Flooring Inspection Training Services in Tulsa, Okla., responds: While there are several possible causes for the cupped flooring, condensation due to a lack of insulation probably isn’t one of them. Cupping is always caused by a moisture imbalance from the bottom up, either at the time of installation or over the life of the flooring. Because the cupping seems to be evenly distributed over the entire house, the most likely cause is that the moisture content in the subfloor was elevated before installation and the flooring wasn’t properly acclimated. To prevent such problems, the moisture content of the subfloor and the new wood flooring must be within 2 percent to 4 percent of each other prior to installation.
Another possible cause is that the plastic covering the dirt in the crawlspace isn’t sealed to the walls or doesn’t cover the ground completely, elevating the relative humidity underneath the floor. Inadequate cross-ventilation in the crawlspace would compound the problem; typically the area of the vents should equal 1.5 percent of the total square footage of the house.
It’s also possible that the floor was mopped at some point with an excessive amount of water; this too could lead to cupping.
Once the source of moisture is found and corrected, the floor should be allowed to dry for at least a year to see if further action is needed. Unfortunately, if the planks have cupped enough that there is edge crush on most of them, they will not go back to normal, and the floor will have to be refinished or replaced (prefinished flooring with an aluminum oxide finish can be very difficult to sand). It might be that your only option is to tear out the old floor and install a new one per the flooring manufacturer’s instructions.
