Most newer homes have some insulation under floors. Older homes may not. If the floor is above a basement, then the basement ceiling insulation is crucial to preventing heat loss. Spray-foam insulation does an excellent job of insulating and filling the spaces around the electrical wires, pipes, and other obstructions. The most common is fiberglass batt insulation which can fit more easily among pipes and joists.
It's a good idea to add a vapor barrier over the basement ceiling insulation as a practical way to prevent heat loss and to protect the insulation from mold and mildew. It's vital to secure the insulation to the joists so it doesn't come loose and rest on the vapor barrier.
Stay tuned for more on insulation!