My brother-in-law finished building a log home last year and had a beautiful hickory hardwood floor installed throughout the house. We went to visit him this last summer, which was a particularly hot and humid one. I noticed that every board in the floor was cupped, like upside-down Venetian blinds. It was driving him and his wife nuts, and they’d already talked to the installer about sanding the entire floor flat again and then refinishing it. Then we started talking about why this would happen. Later in the day, it came up that he had a dehumidifier going 24/7 down in the crawlspace. The space under the house was as dry as the Sahara desert. Eureka! The problem was obvious. The undersides of the floorboards were bone dry, while the tops that were exposed to the heat and humidity had much higher moisture content. The board tops were swollen while the bottoms were shrunken, causing the cupping. He unplugged the dehumidifier and a month later the floor was as flat as a billiard table.
By the way, if you’d like to see how to install a hardwood floor from scratch, go here: How to Lay Hardwood Floor With a Contrasting Border
— Travis Larson