A floor that touches nothing
A floating floor is locked together plank to plank and sits loose on the underlayment. Nothing holds it to the subfloor. That is what makes it fast to install and forgiving of minor imperfections, and it is also why it moves as one piece: a 20-foot run of laminate can change length by a noticeable fraction of an inch between a dry January and a humid August.
Where it goes
The expansion gap is a quarter to three eighths of an inch, or whatever the product specifies, at every wall, cabinet, island, fireplace, door jamb, pipe and transition. It is covered by baseboard, quarter round or a transition piece that is fastened to the wall or the subfloor, never to the floor. Nothing is ever set on top of a floating floor and fixed in place; islands and cabinets go in first and the floor stops at them with a gap.
Run-length limits and transitions
Products specify a maximum run before the floor needs a break, often in the range of thirty to fifty feet, and a maximum total area. Beyond that, a T-molding or flush transition in a doorway lets each section move independently. Whole-house floors are planned around these limits so the breaks disappear into the layout.
Acclimation
Flooring that arrives cold from a warehouse and is installed the same day expands when it warms and takes on the house's humidity. Acclimation, usually 48 hours flat in the rooms at living temperature, lets it reach equilibrium before it is locked together.
Underlayment and moisture
Vapor from a crawl space or slab adds moisture to the floor from below and drives expansion; a vapor-barrier underlayment and a subfloor that meters dry are part of the same system as the gap.
Diagnosing a problem floor
Lifting or peaking in warm months: expansion with no room, or a pinned floor. Gaps in winter: shrinkage, often after a summer install without acclimation. Hollow spots: subfloor dips. Movement when walked on: joints not fully engaged or an unflat subfloor. Cupping: moisture from below. Each points at an installation condition, which is why warranties require them and why installers follow them.
If it is already wrong
Relieve the perimeter: pull baseboard, cut back the floor to restore the gap, check for anything fastened through it. Free pinch points under cabinets and transitions. If the floor has buckled hard or joints have broken, the affected area comes up and goes back correctly, which is why a box of attic stock matters.
