Every August the same post appears: a floor that was perfect for two years has lifted into a ridge somewhere in the middle of the living room, and nobody touched anything.
The thread almost always lands on the expansion gap — that the installer ran the plank tight to the wall, or trapped it under a heavy cabinet, or caulked the perimeter. Those are all real and they're all worth checking first. Pull the quarter round in a corner and look. If there's no gap behind the baseboard, you've found it.
What gets missed is the other cause, and it's the one I see more often in newer houses: the run was too long to float at all.
Every floating floor has a published maximum continuous run — commonly somewhere around 40 to 50 feet in either direction. Past that, the accumulated movement across the field is more than any perimeter gap can physically absorb, no matter how correctly it was left. A great room, kitchen and hallway laid as one uninterrupted sheet in a modern open-plan house clears 60 feet without anyone thinking about it, because it doesn't feel like a long run. It feels like one room.
So the floor behaves for two mild years, then meets a genuinely hot August with a slab that's warmed up, and the expansion goes the only direction left to it — up, in the middle, where the field is widest.
The fixes are unglamorous. Either break the field with a transition at a doorway so each section is inside tolerance, or glue the floor down, which removes the constraint entirely because a bonded floor can't move as a sheet. Most people want the second one once they understand the first means a strip across an opening they specifically designed to feel continuous.
Worth measuring your actual run lengths before assuming it's the gap. If the longest straight line in your floor is over about 50 feet, the gap was never going to save it.
More on how the material moves on a slab: waterproof luxury vinyl plank.
