Crawl space or leak in kitchen to blame for cupping?

Q: I have a problem with my red oak hardwood floor cupping. It started slowly at the island in the kitchen and has spread slowly. The floor is less than 4 months old.

With background – I had a hardwood floor installed in a foreclosed home that I bought. The home initially had water damage and hence we had to remove the entire subfloor and install new boards, then tar paper (felt paper) was laid, and then the hardwood was laid. The hardwood sat in the home for over a week before installation. The man that installed the floor has done this type of flooring for about 20 years.

The house is over a crawl space that does have some moisture issues. There is proper ventilation, but we have not gotten to laying a tarp on the dirt. I just recently notice a leak under the kitchen sink due to an improper installation by a plumber. I am not sure where to place the blame.

I would like to know if moisture can get from a crawl space, through the tar paper, to the floor and cause the damage, or if it would be more likely the plumbing that has caused the problem? Also, is it possible the floor could return normal? We live in Michigan.

A: Cupping indicates excessive moisture moving from the bottom of the floor to the top. Of course a wet crawl space is something you want to attend to. The felt which was installed first serves as a moisture retardant. I wouldn’t view it as a vapour barrier since it has dozens of holes punched through it when nailing down the floor. Laying out a tarp on the dirt should help. However, the leak at the island sounds like the most likely source of the problem.

I have seen floors flatten out in time. You will need to be patient and give it that time to thoroughly stabilize and see what it does.

Sanding a floor before this moisture stabilization occurs would likely lead to the floor crowning, which is reverse cupping.