Glue down hardwood floor separating at joints

Q: My parents had hardwood floors installed in their home a little over a year ago. They live in a home that is about 8 years old and the 3 rooms that had the flooring put in all had carpet in them previously, which was properly removed. Then the floor was levelled. This weekend the flooring started separating at the joints, in random parts of all 3 rooms, which are in different parts of the house.

The installer is a friend of mine and he had never seen or heard of such a thing. The flooring was purchased from my work, and when I spoke to the decorator here she said that it has to be an installation problem. The installer knows he used the correct type of glue, but have you ever heard of a floor doing this after being down long? The house has no structural issues.

A: This floor is glue down? It sounds like the sub floor is shrinking and the glued down floor is separating at the sub floor seams. I’ve seen it only a few times in 40 years, even on very old floors. It stands to reason, the finished floor will react to what the sub floor is doing. I would put a moisture meter on both the finished floor and sub floor if you have access to that. They should be within 4% of each other. You may also check the humidity level by placing a hygrometer on the floor for a short time, say 15 minutes. I feel fairly confident the issue is the sub floor itself. What was used to level the floor? If water was added to the sub floor along the joints (I assume it is sheets of something) it may have expanded and then as it dried it shrunk.