Hardwood floor buckling

[Larry Flanagan]

I recently had hardwood floors installed in my residence.  I am experiencing some pretty significant buckling in places.  In the worst spot, I cant even open my back door because the new floor has expanded and raised up so much.  I think I may have a moisture problem at the back door so I am planning on replacing the door.  My floor guy said to run a dehumidifier in the basement for a month and then he will come back and fix the boards.  I really dont think the basement is my problem.  I have a finished walkout and its drier down there than it is upstairs. But I had a dehumidifier sitting around so I have it running now and set at 50% RH. My main level is probably 70-80% RH. The portion of the room with the biggest problem extends out from the house so there is no basement underneath.  Its about 3' x 5'. What can I do to that part of the floor to keep the moisture level from getting excessive?  Some sort of vapor barrier and/or insulation?  I should do something in that space when the door and floor are ripped out.  Any comments would be appreciated on how to remedy this situation.