A flooring system is a group of components fastened together that make up a floor. Most flooring systems require support at two sides opposite each other. This support comes from concrete or cement blocks that are part of the foundation or from wall framing or steel girders when the floor is at the second story or higher.
A common flooring system using dimensional lumber has three components: beam, joists and subfloor. The beam spans the distance between two sides of the floor to add strength at the middle point. The joists are typically 2 by 6s or 2 by 8s on edge, running perpendicular to the beam with their center points resting on it. The subfloor is 3/4-inch plywood or oriented strand board (OSB). These 4-by-8-foot sheets lay across the top of the joists where they are fastened with glue and screws. The finish floor sets on top of the subfloor.
Trusses provide strength, rigidity and predictability, and take the place of joists in this type of flooring system. Made from high-grade lumber or from laminated lumber products and manufactured under controlled conditions, they won't change over time like dimensional lumber often does by shrinking as it dries. Two popular types of truss flooring systems are used: open and closed web. Open web trusses look very similar to roof trusses with lumber running diagonally or up and down between a top piece, or top chord, and a bottom piece, or bottom chord. These do not have to be cut, so builders can easily run plumbing pipes, heating and cooling ducts and electrical lines through them. Closed web floor trusses have laminated lumber between the top chord and bottom chord. Builders have to cut holes to run utilities through them, and specifications dictate the sizes and placement of the holes. This flooring system also is covered with 3/4-inch plywood or OSB. Since trusses span longer distances than dimensional lumber, these floor systems may not require beams.
Many commercial buildings use concrete floor systems. The building frame is built from steel I-beams and girders. Cast concrete is set in place on the frame with cranes. These concrete floors also serve as the ceiling for the floor below.
Computer rooms, buildings where data is stored and cleanrooms in manufacturing buildings use raised flooring systems. These allow access to utilities and wiring below the floor and help with cleanliness and temperature control. Many variations of these exist, but a standard one uses pedestals. The pedestals sit on the floor in a grid layout and the floor panels sit on top of them with the corners of four panels meeting at each pedestal.