I have installed 12mm laminated floors. They have been in since late 2007. They are now pushing up on the long joint section. I seem to think it happens when it rains a lot. What will cause this and what can be done about it. I have done the job myself! I do have the 8mm spacing from the wall and the underlay is the one you get when you don't specify the thickness. Much appriciated.

Is this over a crawl space? Over Concrete? Or over a wooden subfloor over a basement?