Laminate flooring must be installed over a sub floor which is clean smooth and leveled.Laminate can be installed over existing hardwood floors installed over a wooden subfloor without a vapor barrier. Hardwood installed over a concrete floor must be removed prior to installing a laminate floor. Since the hardwood is not going to act as a vapor barrier, vapor barrier would have to be installed. If this was done by putting vapor barrier over the hardwood it would trap moisture between the concrete and the hardwood causing it to mold and rot.
Laminate can be installed over vinyl or tile but will require a vapor barrier if over a concrete subfloor.Laminate can not be installed over carpet or carpet pad so these items must be removed prior to installation. Installing laminate over carpet or carpet pad can cause the floor to have too much deflection. This adds stress to the locking system and can cause it to fail over a period of time.When installing over concrete vapor barrier is always required.