Hardwood Floor Cupping and Crowning
Cupping occurs when the edges of a board are high and the center of the boards is lower. Crowning is the opposite of cupping, in that the center of the boards is higher than the edges.
Cupping is caused by a moisture imbalance through the thickness of the wood. For example, the wood is wetter at the bottom of the board than on the top. If excessive moisture is the cause, identify the source and remedy the problem. Then, allow the flooring to re-acclimate to the new, drier environment. After drying to normal conditions, the flooring should flatten.
Some slight cupping and crowning can occur naturally and should be tolerated. They are usually only slightly visible unless the floor is viewed across boards and against a strong low light source such as a patio door or window wall. It is often noticed while the house is still unoccupied, but furnishings make it seem more normal as the strong light reflection is softened and angles of view are changed. Over time, the cupping will subside.
