What shows on the floor first
Foundation trouble usually reaches the floor before anything else. Doors that rub or will not latch, hairline cracks running through tile and grout, gaps opening along a baseboard, and a floor that rolls instead of lying flat are the signs people notice in the house.
A new floor makes those signs impossible to ignore. Click-lock vinyl and laminate float over the subfloor and need it flat, so a dip or a hump underneath can lift a seam or make a plank flex. That is why leveling is part of the installation agreement, not an extra the customer discovers later.
