Ok here goes, bear with me a bit. 9 years ago we had 3 1/2 inch red oak hard wood floor put in. i have radiant heat so i was told by my heating peeps to let hard wood installers know that they should use shorter nails when installing the hard wood so that no nails wouldn't hit pex tubing for heat. my installers said they would use a shorter nail. i had floors done in whole house upstairs and down stairs. i have no problems upstairs but on first floor i have every 1-2x a year for a few months buckling in one spot. it does usually go down but this year its really bad and i want it fixed. i took off baseboard and cut out sheetrock to give more room for wood to expand. everything was really tight so i thought it would go down a lot but it didn't. part of issue is the wood starts to buckle in family room and a little in kitchen, but the wood runs from family room to kitchen and even dining room all one row connected like one big floor. so i'm not sure if i would need to relive other spots as well for more space to expand. my plan right now is that there is room for floor to go level with less impingement, and once it does hopefully go back i can nail the wood flat to subfloor and hopefully next time it won't swell so much. i didn't not run a/c this summer that much didn't need to so i know that the humidity in home is what made it swell so much. it almost doesn't even seem like they nailed the wood down very well in this spot allowing it to buckle but i'm not sure. the installers sold the buisness so no help contacting them. one question is what type of nailer would i use for this? as much as i dont' want little nail holes on my pretty floors at this point i want a flat floor that doesn't buckle and makes less creaky noise when walking on it!!

Lots of things can cause buckling. Like bad fastener schedule ie; fastener spacing. A small leak. The crawl space is to damp, lack of expansion space.