We ran into an unanticipated problem with our 3/4 inch Brazilian Cherry floor. We had it installed in a second floor room that sits entirely over a garage and acclimated it for 3 weeks at a consistent temperature (72F) during the late fall in Houston, Texas. The installer used nails directly into the plywood. It's now summer in Houston and the humidity has skyrocketed. We still have the room at a consistent 72 degrees, but the garage below the room, which is insulated but not climate controlled, is now very warm and I imagine very humid. The floor has started buckling very bad in several places, to the point where when you stand on it it bounces up and down like a trampoline.

My first question is this: What is the most likely culprit? The humidity in the actual room, the humidity level in the garage below, or a combination of both?

Also, what can we do about this? Purchase a dehumidifier? If so, do we stick it in the garage or the actual room? Do we need to pull up the floor and have it re-nailed?

Thanks for any help.

Gee, I always worry about that when I am installing over a garage. Of course your going to have to pull it up and if done carefully you can save it. Your goint to have to do some preventative mopisture control either in the garage or in the room. I'd try stapling some six mil plastic to the ceiling in the garage and then a new layer pf sheetrocl. This will keep from trapping moisture up in there than if you did it from above.

Additional to the installation of a vapour barrier on the garage ceiling, I think it would behoove (gawd I love that word) you to place a portable dehumidifier in the space to reduce any humidity in the room.
Unlikely if the floor has actually lifted off the subfloor that it would return to flat condition, so removal and re-installation is most likely necessary.

depends if the floor is cupped or is buckling too diffrent things. If its cupped then the space under the floor is more likerly the culpret. if its just buckled then its probally from the conditions in the finished space along with what is going on underneth. You really need to call the installer and have him come out and take some readings. If the floor has a much higher mc on the bottom then you dehumidify the space below. If its constant through the piece then both spaces need to be dehmidified. You need a balance this is the key. you also need to check the expansion space if you are getting some lift its probally pressing somewhere along the walls or casings.

Well the OP stated that the floor moves up and down like a trampoline. Doesn't seem to be "cupped" if that is the case.

Well im sure that I dont have to tell you about people exaggerating over the internet. Just call the installer its been less than a year. if he is worth his weight in beans he will come out and help.

I've seen alot of those trampoline's when I did inspections. Hope none of my jobs do that, so far so good. Knock on wood!