When moisture buildup in floors occurs, hardwood floor cupping can result.
Cupping, also called "washboard" is a condition where the edges of a piece of flooring (across its width) are high and the center is lower. This generally develops gradually. Moisture imbalance through the thickness of the flooring is the only cause. Moisture is greater on the bottom of the piece than on the top.
A common source of the moisture that causes hardwood floor cupping is a wet basement or crawlspace. This moisture rises up into the home due to what is called the “stack effect” and this creates high moisture conditions on the bottom face of the hardwood flooring. This in turn causes the bottom face of the hardwood boards to expand dimensionally and this creates the cupping condition.