What is the difference between floor and subfloor? Is subfloor a part of floor?
Subfloor is a part of the floor but has a different purpose. Without a solid sheet that spans the joints and the ends are supported, how can you install tile or wood flooring? In the oldest residential constructions I’ve seen, they used either two layers of thick wood planks (bottom acting as a subfloor) or boards run diagonally as the subfloor. Today, we almost exclusively see OSB, but the purpose is the same. It provides even support for the floor.