Some floors are constructed on concrete slabs that are flat on the ground. However, most floors are elevated above the ground. Pre engineered floor framing system is more durable underfoot and allows for access to heating equipment, insulation, wiring, and other machinery.
Floor joists span the spaces between supports like walls, foundations, and beams. They are spaced at regular intervals. The normal spacing between floors is 16 inches, but some floors may have joists that are 12-inch or 24-inch in diameter. Building codes are used to determine the spacing and size of joists. These codes are based upon engineering requirements. Joist headers are perpendicular and cap their ends at the joists.
Subflooring provides a base for finish flooring and also serves as a platform during construction. It may be made of boards laid either at right angles or diagonally across joists. Or the subfloor may be made of plywood or other panel products that are laid perpendicular to the joists.
The thickness and stiffness of the subfloor determine the types of finish materials that can be laid on top of it. Floor joists are placed directly on sills at the foundation. This prevents termites and rots from coming in contact with the foundation. The method of framing used will determine how the floor joists are connected to the wall studs.