Per NWFA:

What it is:

Cupping occurs across the width of the individual pieces of flooring. The edges are high and the center is lower. It generally develops gradually.

Cause:

• A moisture differential within individual pieces of flooring, usually excessive moisture on the underside of the flooring. More subtle cupping can be caused by lack of proper acclimation (this is generally permanent cupping). Potential sources of excessive moisture include:

- Building leaks

- Poor drainage

- Plumbing leaks or overflows

- Leaks from dishwashers or refrigerator ice making units

- Wet or damp basements/crawlspaces

- Concrete subfloors that have not cured

- Plywood subfloors with excessive moisture

- Poor or no ventilation

- HVAC system not operating.

• Flooring also may cup when a wood floor experiences conditions that cause rapid drying on the

surface. This condition occurs with gaps as the flooring shrinks.