Floating-floor expansion gap — leave ¼″–⅜″ at the wall or the floor buckles

What this diagram shows

A cross-section at a wall edge compares a floating floor — laminate, luxury vinyl plank, or engineered wood — installed two ways. On the correct side a ¼-inch to ⅜-inch expansion gap is left between the plank and the wall, sitting over the subfloor and underlayment, and is hidden by the baseboard and shoe, which fasten to the wall rather than the floor; the floor stays flat because it can grow and shrink. On the wrong side the planks are butted tight to the wall with no gap, so when the floor expands it has nowhere to go and buckles, peaking up at the seams.